OUR SECOND AGE: Scene 5

THE BIRDS AND THE BEES

‘We see things not as they are but as we are.’
The Talmud

Around 70 million years ago (25 million years before birds with artistic specializations emerged) plants were creating a very refined form of sexual display, which would take interdependence between diverse creatures in a radically new direction.

It had started millions of years before when some low-growing plants evolved into angiosperms by producing flowers instead of cones and protecting their seeds in an ovary.

When the flowers opened, some of the sticky male cells (pollen) drifted onto a female organ nearby, and so set their reproductive process in motion. Fertilization could take place in the same flower, in another flower on the same plant, or on a flower of another plant. As usual, reproduction involving two plants increased a species’ genetic diversity, and with the wind’s help their pollen spread far and wide.

But now early water lilies and low-growing magnolias were displaying larger, coloured or fragrant flowers, and magnolias were growing taller too. They were vying for the attention of a range of insects and birds that noticed and responded to various hues and scents.

From an evolutionary point of view, it seems clear that the sensitivity of different pollinators to a different range of colours within the floral smorgasbord seems to be another example of conflict avoidance. Plants and animals both benefit from operating within a niche market.

As the insects and birds harvested sweet nectar from flowers shaped to suit them, they collected pollen on their bodies. When they visited other flowers of that species, pollen rubbed off on a female sex organ in enough cases to increase the reproduction rate above that from wind pollination.

Like other plants angiosperms still set more seeds than necessary, and some birds and animals still ate the excess.

Soon some plants were giving their seeds a protective coating so that they could lie dormant for longer, while others started growing nutrient-rich fruit around their seeds to provide ready-made fertilizer for the seed when it dropped and decayed. Some fruit became juicy and sweet when ripe, and even brightly coloured. And so its scent or hue attracted other birds and animals, which either discarded the seeds after eating the fruit or swallowed and excreted them somewhere else.

Meanwhile a few plants began to protect their seeds or leaves with toxins to discourage food-seekers, and a few animals were in turn developing a liver that filtered out the toxins. Today some fungi use not only poison to discourage potential consumers, but also bright colours like red – ignored at the forager’s peril.

All this interaction is based on protecting and passing on diverse ways of being alive, and communication within the system is an integral part of that.

(One example of Australian flower and animal coevolution is the nectar-flow of banksias and grevilleas in certain areas. It coincides with the breeding season of local honey-eating birds, with their specialised brush-tipped tongues. And it also triggers the breeding season of their predators: kookaburras, goannas and snakes.

(Honey-eating and fruit-eating mammals that feed at night, like possums and bats, are also part of these ecosystems. As today’s bush-regenerators in the Blue Mountains know only too well, in disturbed ecosystems some exotic plants also successfully co-opt native animals, particularly birds, in generating and spreading their offspring.)

The mechanism of an animal’s colour vision is an integral part of its way of living. Flower, fruit and insect harvesters need tg be able to distinguish colours, often including those in the ultra-violet part of the spectrum, while animals that feed on grass or meat have little or no such need.

The physics and chemistry involved in the actual production of colour, however, is much more complex.

As it is in Earth’s rocks and minerals, it seems to be basically a matter of a range of pigments, a process that started as we have seen with the green photosynthesizing pigment chlorophyll. But in birds like peacocks and flying insects like butterflies it is often a process of developing a series of reflective surfaces that scatter light into a range of colours.

Theories based on either random or creative evolution cannot yet explain how this emerged, or how the wonderful complexity of colour and light used by a range of animals in communication emerged. (A not-so-well-known example is seen in today’s cuttle-fish gathering to spawn off Australia’s south coast.)

Back in our story several flying insect families engaged in co-evolution with flower-bearing plants were by now undergoing a more drastic kind of metamorphosis - from a soft larval form through pupation into a very different adult form.

Their transformation within the pupa is very mysterious. The cells making up the larva break down into a genetic soup, from which adult cells gradually emerge, divide, multiply and differentiate.

A few biologists think that this is a remnant echo at the cellular level of an ancient battle, in which an early flying insect took over the body of a soft-bodied crawling insect. If this remarkable theory is true, it is yet another example of competition being transformed into joint effort.

Some of these insects were also creating distinctive social groups. Like dinosaurs and mammals they limited the number of offspring, and then spent a lot of time and energy looking after them - but they had an idiosyncratic way of doing it.

Their strategy was to clump lots of infertile females around a very fertile ‘queen-mother’, with a few males being specially produced just before her single mating-time.

The colony‘s members built a communal home around her eggs and helpless larvae and then formed separate nursery and defence cohorts, using chemical signals to communicate with each other in an instant. Most scientists describe such groups as operating like a complex organism because they work in such close co-ordination - like cells in a single being.

As anyone who has kept bee-hives knows, warrior bees in a hive that has lost its queen fight in wave after wave of suicide squads. And ant warriors are particularly aggressive in the first years of a colony, when they have many young to feed and only a few adults foraging for food.

Of course most metamorphosing insects did not develop societies. Today, like virtually all spiders, and like monotremes, they live alone but for a brief and dramatic mating. Some, like moths and butterflies, lay their eggs on a beautiful tasty leaf, from which the larvae crawl onto other leaves, eating and growing until their biological clock tells them to pupate. And some, like wasps, carefully prepare a burrow and lay their eggs inside in or on a ready-to-eat meal – either still alive or specially killed.

(Many Australian native bee species are also solitary – and stingless. We are only beginning to appreciate their uniqueness and diversity. Our iconic social insects are termites - either inspiring home-builders or devastating home-wreckers, depending on your point of view. They have also made themselves useful to people in northern Australia over thousands of years by hollowing out tree branches, which men then use to make a unique musical instrument – the didjeridoo.)

Today we see social bees, wasps and ants as the embodiment of vigorous protection of one’s territory against outsiders. Whether it emerged among them or not, territorial protection is an essential part of coevolution, limiting local population growth and thus reducing potential competition for resources, and also enabling the development of self-protection skills.

Most animal species today see protection of territory from outsiders and local competitors as a top priority whether they live in groups or have a solitary lifestyle. Plants are also territorial to different degrees. (In the Upper Blue Mountains the most notorious examples are noxious weeds like blackberries and montbretias.)

As we have seen with colour vision, the members of each species within an ecosystem perceive only a fraction of the total reality of their territory. They take in only what they need to know in order to have a chance of surviving and thriving. Since their most urgent needs relate to food and water, reproduction, and avoiding or escaping danger, they generally see the world through this frame of reference (whether instinctive or learned).

At this point in our story a flowering plant’s frame of reference for an insect was its hairy legs and wings (pollen-courier). A plant-eating dinosaur’s frame of reference for a tree was its tasty leaves (browser food). A dung beetle’s frame of reference for a dinosaur was its tasty warm dung (dung beetle food) and big feet (danger).

The point is that such frames of reference are absolutely functional - as long as there is no sudden change that threatens a whole eco-system’s survival.

But around 65 million years ago Earth’s Fifth Major Mass Extinction occurred. Tectonic movement had separated Africa and South America, pushed India north, almost split Australia and Antarctica and moved Africa’s northeastern corner closer to Eurasia. Now the Atlantic Ocean was widening, with the usual violent disturbances.

(New Zealand had also begun breaking away from Australia, warping its east coast, and pushing up the Great Dividing Range.)

Then an asteroid with a diameter of about 12 km hit Mexico on today’s Yucatan Peninsula (at the time under shallow water). It left a crater 170 km wide and ruptured into several huge segments that apparently flew into the air before returning to make further devastating impacts. Earthquakes and tsunamis occurred across the globe, along with acid rain, a global firestorm and a huge cloud of dust, which blocked out the Sun’s light and heat for many months.

In the following mass extinction ecosystems that had flourished for millions of years started to break down. Within a few thousand years 65% to 70% of species were made extinct, including many animals in the water and on land and virtually all those on land weighing more than 20 kilograms as adults. Among those that disappeared were the iconic ammonites and around 1,000 species of dinosaurs - an order of land-vertebrates that had been extremely successful for 160 million years.

Remember that this transformational change was due to a completely unexpected series of events, and thus beyond the capacity of most animal species to adapt. Earth’s environment may be largely supportive, but it can never be absolutely stable.

And yet many species of insects and also of some small birds and mammals managed to survive both the initial catastrophe and its long-term effects.

Perhaps this was the original stimulus for migration in birds. They would have had to fly long distances in search of isolated patches where the environment was not so hostile. We will come back to this in ‘Our Third Age’.

Meanwhile small mammals were no doubt helped by their ability to regulate their body temperature, together with their furry skins, burrowing skills and nocturnal lifestyle - as well as their practice of getting protein from a wide range of insects.

But from our point of view the main effect was the demise of large dinosaurs, because it cleared the way for a wider range of mammals, including us, to evolve in spectacular ways.

* * * * * *


(More Google images - click to enlarge)

OUR SECOND AGE: Scene 4

CREATURES GREAT & SMALL

‘When the head is empty,
then you become aware suddenly
that a bird is singing over there.’
Masanobu Fukuoka

By around 150 million years ago, at the beginning of the Cretaceous Period, Gondwana and Laurasia were splitting even further, continuing the process that would lead to today’s continents.

Bird-hipped dinosaurs had long since joined lizard-hipped dinosaurs in the expanding, diversifying forests. They included several armoured plant-eating species like the most recognizable dinosaur for most of us, Stegosaurus. They defended themselves from carnivores with spikes and horns on their heads, backs and tails.

And the lizard-hipped dinosaurs now included plant-eaters that were the largest land animals ever. These were the Sauropods – up to 30 metres long (much of this in their flexible neck) and 100 tonnes in weight. From the trees’ point of view they were a very challenging predator, but they were generally slow-moving and gentle, except when they had to use their powerful tails to defend themselves or their young.

There were also large dinosaur carnivores that preyed on the browsers’ young. (In a part of Australia now within the Antarctic Circle, Giganotosaurus species were preying on the gentle Muttaburrasaurus.) Child-care was a must, and some browsers apparently had communal nests, where they shared responsibility for hatchlings.

Now many species of quite small dinosaurs were emerging, such as the rabbit-sized Microceratops - on the ground, in the trees, in the water or in the air. There were also lots of new amphibians such as frogs, and new reptiles such as crocodiles – as well as the Quetzalcoatlus (named after an Aztec god), which had a 15 metre wingspan, making it the biggest flying life-form of all time.

And a few true birds were emerging and starting to diversify. (Fossilized feathers from this period have been found in Victoria, and a small bone in Queensland.)

They would go on to create many ways of caring for their young, including lifetime pair-bonding with nurture from both parents; communal nesting; and forced fostering.

(In Australia today several birds have unusual nurturing behaviours. The emu father hatches and protects the eggs. Mud-nesters like white-winged choughs share the caregiving across their whole community. And parasitic cuckoos lay their appropriately pigmented eggs in the nest of a selected local bird species.)

Some bird species actively demonstrate the behaviour their young will need in adult life This among other things has led to much rethinking about birds’ ability to learn. They need light bones and small brains to fly successfully but this does not mean that they are ‘birdbrains’.

As we shall see, intelligence is evident in some behaviours that are linked to sexual selection and have to be learned and improved on throughout a male adult’s life. It is also seen in the ability of a few bird species to adapt to, and thrive in, our built-in environment.

However most birds cannot adapt quickly enough when humans invade and destroy their breeding habitat. When the tipping point is reached, most die out and we are left with bigger and bigger populations of fewer and fewer species.

(Australian researchers are noting the different functioning in birds’ right and left brains – one eye searching for food, while the other keeps watch for predators. They are also able to take in and store new information in an urban environment, and incorporate it into their daily behaviour. Indian mynahs have been seen using a discarded plastic bag as a nest-liner. Song-birds can learn human songs, using the left side of their brain. Cockatoos have been taught to use human language in a meaningful way.)

Back in our story a new kind of mammal appeared in what would become South America.

Like monotremes these tiny shrew-like marsupials were nocturnal omnivores. But the one or two fertilized eggs of the females developed into tiny foetuses inside a simple womb and were released through a very small birth canal (or vagina). Each foetus felt its way up towards her nipples deep in an external pouch, with maybe only one of a litter actually reaching it. Once there it latched onto a nipple, and drank from it until old enough to emerge and learn to forage for itself. Even then it still slept in the pouch and sought refuge there when necessary.

In this period India had split away from Gondwana, but Africa and South America were still connected, and Antarctica was joined to Australia and South America by continental shelves. Since Antarctica was warm enough at this point to support plant-life a few marsupial species from South America migrated across it into Australia.

(They were the ancestors of the wide range of marsupials that live here today, retaining the nocturnal lifestyle adopted for living with dinosaurs, because it is equally fitted for Australia’s predominantly hot and dry climate.

(During this period high sea levels covered much of southern Australia and divided the rest into four islands, around them the shallow Eromanga Sea. It was home to many large marine reptiles, like crocodiles, which looked after their hatchlings, and were essentially the same as today. And on the muddy sediment on the floor of this sea were many animals, whose fossils would later be opalised by the action of water. Today they are mined at Coober Pedy, White Cliffs and Lightning Ridge.

(Volcanic activity was raising the Great Dividing Range along today’s eastern coast, and what would be the north of Australia was a paradise for dinosaurs. Among them were a small plant-eater, Wintonopus, and one of its predators, Tyrannosauropus, about 12 metres long.)

There were also modern ranging spiders in the forests now - on the forest floor under the leaf-litter. They lived for only one or two years, but their mating behaviour, usually conducted on a tree-trunk, was similar to that of primitive spiders.

(In today’s Sydney, one descendant of these spiders often comes into our homes to shelter from the rain, usually taking up position on the cornice between wall and ceiling. It is a Huntsman, of the Isopoda or Delena species, quite large, and moving quickly when disturbed. But it is no danger to humans. On the contrary, it helps control flies and mosquitoes, and puts on speed only to scuttle away from us as fast as possible.

(It is unusual among spiders in that its courting is gentle and even affectionate – the male is smaller but in no danger. The female also has a well-developed maternal instinct. She spins a pure white egg-sac in a rock crevice or under the bark of a tree. And then she fasts for several weeks, staying with her spiderlings until they are strong enough to disperse.)

Now early placental mammals evolved, with more complex brains than marsupials and interactions between their nerves and hormones that are the basis of ours. This suggests a similar range of sensations and a similar responsiveness to internal stimuli.

Their foetuses finished developing in the womb, absorbing nutrients through a placenta, and the mother’s womb and birth canal evolved accordingly. Their young could move independently soon after birth but returned to suckle for some time.

As among monotremes and marsupials, the females still lived with their young, and the males appeared only at mating time. Like earlier mammals they relied on a strong sense of smell, and although they had a wider variety of emotions these were all linked to eating, escaping danger and specific gender roles. The world of giant dinosaurs was hazardous, but some were paving the way for primates by living in the trees, and a few others even seem to have stalked and eaten dinosaur young.

Meanwhile adult male dome-headed dinosaurs were fighting over sexually disposed females by bashing their tough foreheads together until one prevailed.

However in a few animal species less ‘boneheaded’ males were now wooing females with a specific sound, and perhaps even colour. Early serenaders included crested dinosaurs, a few bird species and insects like cicadas. In each case this required the females to distinguish the appropriate sound or colour and respond accordingly.

So the brains of both genders were undergoing significant change, in the form of pre-programming in the central nervous system. This can be seen today in species where the females select the males that are best able to perform a rigidly repetitive call or dance, or are most striking in their adult appearance.

But this possibility of using creative persuasion rather than combat would also lead over time to the emergence of several bird species whose sexual display of intricate songs, bower building or mimicry requires a great deal of learning by practice.

(In Australia today whipbirds, tiny bright blue fairy-wrens, bower-birds and lyre-birds are examples of this diversity and creativity.)

Sometimes the artistry is also part of a camouflage strategy, which birds share with many insects.

(In the Blue Mountains of NSW Crimson Rosellas freeze when alerted, hiding very successfully among the branches of a eucalypt. Their beautiful colours merge with the tree’s older green leaves, its young crimson tips and the patches of blue sky behind.)

But sexual display is usually what evolutionists call costly signalling. A verbal translation of their artistry could be: ‘Wouldn’t you like offspring as wonderful as I am?’

Since it has to be balanced by security considerations it is more likely to develop (and go to extremes) in species without significant coevolving predators. And males with elaborate visual or auditory displays can’t be expected to be faithful partners or nurturing parents. On the contrary they are usually very promiscuous – you could say ‘all show and no help with the kids’.

The best-known examples are peacocks with their superb but cumbersome tails, or the various spectacular birds of paradise in New Guinea’s rainforests.

The females in these species are obviously choosing the fittest male on different criteria from those used by females in species where the males are non-showy, and more obliging. Diversity is clearly an integral part of evolution here as it is elsewhere.

(Meanwhile among the long-living primitive spiders, the Trapdoor Spider had emerged in Australia, named for the camouflage lid that most of the family make on their burrows today. They shelter from their predators there, and also wait for passing prey, rapidly snatching them and then disappearing again. They are rather timid with humans, and so of little danger to us.)

* * * * * * *
Diagram of the concept of
three layers in the human brain
formed as our ancestors evolved

Dramatic illustration
of how the three interconnecting layers function
(Two more Google images - click to enlarge)

OUR SECOND AGE: Scene 3

DINOSAURS PLUS

‘The very first requirement for ecological stability
is a balance between the rates of birth and death . . .’
Gregory Bateson

The next significant part of our story begins in what paleontologists call the Triassic period, around 240 million years ago, when reptile families were diversifying after the Third Major Mass Extinction. Among them were the ancestors of dinosaurs, which, although not direct ancestors of humans, would introduce ways of being that contributed hugely to subsequent evolution.

Among the reptiles were also the ancestors of mammals, which were cold-blooded like reptiles, but had earbones and jaws that moved back and forth.

One was the pig-sized plant-eating lystrosaurus. (Around this time what seems to have been a lystrosaurus left tracks above a layer of coal, recently rediscovered in today’s Bellambi Colliery near Sydney.) There were also stubby-legged carnivorous mammal ancestors that scientists call cynodonts.

Plants were also diversifying, as Pangaea started to break up into two smaller supercontinents. In the north was Laurasia: today’s Eurasia with North America attached to its west coast. In the south was Gondwana: today’s India, Africa, South America, Australia and Antarctica all joined.

A minor mass extinction was followed 35 million years later by the Fourth Major Mass Extinction, and renewal probably took 100 million years.

But then, as the supercontinents kept fragmenting, animal diversity would return and increase as they filled the niches caused by isolation. The scientific term for this is convergent evolution. A later example is six kinds of carnivore with sabre-teeth, all emerging independently in similar but dispersed ecosystems.

As part of this process several dinosaur species were now evolving and multiplying on different continents. They seem to have been descendants of reptiles and forerunners of birds - scaly at first, but with a few eventually being able to regulate their body temperature, and in the process developing feathers.

Like reptiles and amphibians, they had proportionally small, simple brains and acted mostly by instinct, but their legs were strong enough for them to stand upright and this gave them a distinct advantage.

The first ones were what scientists call lizard-hipped dinosaurs, mostly carnivores running on very strong back legs and using short forelegs to grasp a reptile or amphibian as they killed it with a bite. But soon there were some browsing dinosaurs moving on four legs.

A few of them apparently lived and travelled in groups, but they seem to have been no more than acquaintances, clumping together to present a solid front as protection from the carnivores. They spent most of their time consuming the plants that were all around them.

By now in the forests more primitive trees had given way to cycads, gingkos and early cone-bearing trees (conifers), with tough branches and leaves. Nevertheless the browsing dinosaurs were able to eat and digest them - another example of coevolution.

The new trees put their male and female organs in the centre of a cone, and their male cells in grains of pollen. When the cones opened, some of a male cone’s pollen drifted onto the organ in a nearby female cone. Then the female cone closed up to protect the fertilized seeds as they developed, and later re-opened to release them onto the ground.

Any nearby dinosaur excreta provided a rich fertilizer to aid germination, and there were also enough seeds for some to be consumed by various passing animals.

Some dinosaur families were taking an even more significant evolutionary step. Their females laid fewer eggs than reptiles, and both parents protected, warmed and turned them, and then fed and protected the hatchlings.

Since this behaviour called for a very important new way of knowing and interacting, the hormonal activity that signalled pleasure and pain through their nervous system must have expanded.

A very significant new way of living as an animal had emerged: support of one’s young.

Supporting hatchlings required other kinds of brain expansion in adult dinosaurs. They had to keep them supplied with food, and they also had to keep track of a number of older, mobile, offspring.

So they must have developed an awareness of quantity and number – admittedly very basic by later standards. A rough verbal translation of their processing of quantity might be: ‘Have I got enough for them this time (or do I have to go out again)?’ And of their processing of number: ‘I think there should be more than one of them here.’

Meanwhile a few dinosaurs were leaping across the ground, gliding from tree to tree, and perhaps even flying short distances.

Among them were ancestral birds, with teeth, long bony tails, clawed digits, and primitive wings that may have been used for cooling or gliding rather than flight.

In the early conifer forests as well were the first tiny mammals, most only a few centimeters long and making a living as far out of the way of adult dinosaurs as they could.

Like all other existing land-animals but unlike later mammals, the females still had a cloaca (single cavity) - hence the name of their living descendants: monotremes, literally ‘one hole’. And like all other land-animals apart from some dinosaur species, the adults led a solitary life, with the male joining a female only to mate, and often having to fight off or wear out any other males first.

(Today monotremes are extinct everywhere but in Australia and New Guinea. They include the echidna and the platypus, a cat-sized distant relative of which would appear later in a Gondwanan rainforest – on today’s Lightning Ridge.)

Monotremes differed from reptiles in quite a few ways.

Firstly they were warm-blooded and furred and so they could spend the day asleep in a burrow, coming out to feed and mate at night when most dinosaurs were asleep. Secondly they had efficient smell-sensors that helped them find their way to high protein food as quickly as possible. They ate mostly seeds, insects, eggs and small reptiles, and with a fast metabolism they needed food several times a night.

But the most significant difference was that a mother nurtured her young, and she did it in a surprising new way.

She laid a few fertilized eggs in a burrow, but when her tiny hatchlings emerged they were naked and very immature. She kept them warm, fed them with milk oozing through pores in her soft belly-skin, and protected them from any animals that would regard them as food – until they developed the form and agility they would need to survive on their own.

This nurturing was part of a reproductive cycle coordinated by the hypothalamus, a master-gland evolving as part of a new layer around the pre-programmed brain she inherited from reptiles. (Scientists call this new layer a cortex.)

A monotreme female’s hormones ensured that she came into heat (or oestrus), sent out a ‘Come and get it’ scent, and then tested the fitness of responding males by leading them on a not-so-merry chase. Other hormones later prompted her to protect, nurture and suckle her young.

When a male reached maturity his hypothalamus had a less complex task, co-ordinating hormones that prompted him to respond to a female scent and to compete with other males.

These internal calls for action, most of them particular to a monotreme’s gender, are the basis of our emotions. Since they would develop further with true mammals, it seems clear that a new way of living was emerging: action in response to gendered emotions.

Monotremes were pioneering the sexual specialization that mammals are known for among vertebrate animals, and as part of this process the amygdala began to develop slightly differently in males and females.

Meanwhile some hardy insects like cockroaches were thriving among the plants and other animals. Their descendants would have to adapt very little in order to survive until today (for instance drier conditions led to burrowing and then modified wings).

And they are expected to survive well into the future, no matter what it brings. One of their superior survival strategies is that some of their females keep their eggs inside their bodies until they are ready to hatch, and a few even give birth to fully formed offspring.

Near the ocean-floor were the ancestors of today’s squid, spiral-shelled mollusks whose adult size ranged from a centimetre to two metres in diameter.

During their lives they made strong closely coiled shells, attaching identically proportioned but progressively larger chambers as they grew inside them. They controlled their buoyancy and movement by varying the amount of air and water in the chambers.

Although they were not long-term survivors like cockroaches, their influence would last long after they became extinct. Today they are an iconic example of the various organic patterns that have inspired human ideas of symmetry and rhythm over thousands of years.

(Throughout what is Australia today ammonite fossils of all sizes are commonly found in limestone rocks, formed from the remains of creatures with softer shells.)

Back in our story the supercontinent Gondwana was now beginning to break up. The west coast of Africa was splitting off from the east coast of South America, forming what we call the southern Atlantic Ocean. And India was separate from the western coast of Australia and moving north, creating the Indian Ocean as it went.

A split was opening in Laurasia too, forming the northern Atlantic Ocean between Eurasia and North America.

And the Panthalassa Ocean was contracting into the Pacific Ocean. Of course all these oceans are still really sections of one vast ocean.

(In the areas that would be Australia’s coastline there were great volcanoes along today’s east. And in today’s west, huge lava flows poured up from 100 km below the sea, covering an area of land 200 km wide and 70 metres deep. Several comets and asteroids also hit Australia around this time. One left a 24 kilometre crater at Gosses Bluff, in the Northern Territory. Today it is one of the best-preserved ancient impact sites on Earth.)

In a wonderful greenhouse climate from north to south across Earth, plants with seeds were multiplying and diversifying. Now they included more modern pine-trees, which were creating huge forests everywhere, helped by underground networks of microbes, newly evolved fungi, and earthworms – and also by many insects. And trees, microbes, fungi, earthworms and insects were all thriving.

* * * * * * *

A fossilized ammonite cut in half
to reveal the exquisite pattern of its spiral shell
formed by the animal as it grew larger and larger.

OUR SECOND AGE: Scene 2

ONTO SHAKY GROUND

‘So it is necessary, at least intermittently. . . this thing called sex.
As of course you and I knew it must be.
Otherwise surely, by now, we mammals and dragonflies
would have come up with something more dignified.’
David Quammen

Around 360 million years ago, at a time that marks the beginning of what scientists call the Carboniferous Period, Earth’s Second Major Mass Extinction occurred. The apparent tipping point was extensive rifting and volcanic activity.

About 50% of the existing species were made extinct, including more trilobites and many kinds of early fish. And the transition period of intense experimentation and competition among plants and animals lasted 10-30 million years.

As Earth recovered and warmed, longer-living woody shrubs and trees began to form communities of compatible species. Most, such as giant horsetails and tree-ferns, reproduced themselves asexually by spores from under their fronds or by offshoots from their roots. (Australia’s tree-ferns still do this, clumping around a parent.)

But a few (like Glossopteris in what is now Australia) had much stronger trunks with true branches and also reproduced sexually. Small spore-like male cells drifted onto larger female cells where fertilized seeds then developed. Large forests evolved as trees over-reached each other in search of sunlight and they sent taproots deep into the soil.

It was some time before fungi able to dissolve these ‘woody’ plants evolved. So as the first trees died and fell their energy was stored in their remains, which piled up and compressed into vast peat deposits.

Over millions of years of external pressure and internal heat some was progressively transformed into the various stages of coal: soft brown coal; bituminous coal; and finally shiny black anthracite. At each stage there was a higher percentage of carbon, and therefore more stored energy. Trees are about 50% carbon (dry weight); peat is about 60% carbon; and anthracite is about 95% carbon.

Eventually, in places under extreme heat and pressure from rocks above, some would even harden and crystallize into layers of lustreless, translucent diamonds. Their stored energy makes them Earth’s hardest natural substance, excellent for cutting other substances, and for being cut into sparkling jewels.

Back in our story, photosynthesis in the large forests was releasing more and more oxygen into the atmosphere. And it wasn’t long before several insect species took flight.

They metamorphosed from eggs laid and fertilized in water through water-living nymphs into winged adults, and helped by their short life cycle, they soon developed new ways to find food or a mate, or escape predators: light bodies, detailed vision and swift expert movement through the air.

Most amazing were the huge dragonflies, with nearly weightless bodies and wingspans up to that of modern seagulls. Since their wings didn’t fold away none of these insect species could hide from predators, but flight opened up a whole new world for them – and for our Universe.

Meanwhile spiders, and some insects, were also experimenting with direct sexual engagement rather than fertilization of ejected eggs. Coupled with eggs able to live out of the water this enabled them to reproduce on land, but their mating was more of an attack than an embrace.

The female was larger than the male and often completed the process by eating him. His job was now done, and, unless he escaped to live just a bit longer, she recycled him into nutrients for her developing offspring. Both sexes took a few years to reach maturity, but she lived for several more years, breeding with a younger male each time.

Today most female spiders and several female insects, such as the praying mantis, still practise partner assassination. But of course several other mating solutions have also evolved, particularly among insects.

Now some amphibians were evolving into thicker-skinned reptiles, with strong legs that raised their bodies slightly off the ground, making them more agile.

Two of the earliest confirmed reptiles were the lizard-like Hylonomus lyelli (forest mouse), which was 20 cm long; and the Proganochelys, ancestor of today’s turtles, 1 metre long and unable to retract its head.

Like insects reptiles practised sexual intercourse, with their own versions of land-eggs and the innovative probing organ invented by male insects (the penis).

Since fertilization within the female's body was less haphazard, reptile females didn’t have to produce so many eggs as fish and amphibians did, and so the eggs could develop in special salty fluids inside the female’s body.

Like all female animals at that time she had a single evacuation and reproduction cavity (a cloaca) through which he ejaculated his sperm. She enclosed her eggs in soft leathery shells so that each offspring could develop inside its own bubble of fluid, and then laid them together on the ground. And as in other egg-laying animals the egg contained enough food to last until they were ready to hatch as miniature versions of their parents, prepared to struggle for survival and maturity on their own.

Since partner assassination was not really an option for reptiles, sexual intercourse for them entailed a whole new set of behaviours.

And there was another complication. As the numbers in a species grew, males often had to compete for access to females. In order to mate successfully he must be intimidating - first to deter any rivals and then to persuade the female to submit.

So in a reversal of insect sexual specialization, reptile males usually became the larger gender, a pattern that would be passed on to most mammals.

But although their mating was essentially coercive rather than seductive, reptiles had inherited dominance and submission postures from amphibians as a way of avoiding conflict, and a successful male wanted as little danger to himself as possible.

So as their brains developed to handle intimate sexual contact, reptiles adopted a clear, intimidating body language among all adults. This is how self-protection by an instinctive choice between dominance and submission evolved, within a species as well as between members of different species.

The sexual behaviours of early reptiles may seem rather crude to us, but they were actually paving the way for mammals’ more emotional interactions – including ours.

Today the pre-programmed inner layer of our brain, loosely called the reptilian brain, still manages not only our involuntary functions such as breathing, digestion and blood-circulation, but also, through a special organ (the amygdala), the instinctive self-protective reactions commonly known as Fight (an evolutionary variant of submission) or Flight (an evolutionary variant of submission).

Back in our story, even though the cells, tissues and organs were co-operating within their bodies, these reptiles themselves generally functioned in their environment as fiercely competing individuals. Just as insects, spiders and amphibians did, reptile males and females had solitary lives outside mating times, much of it devoted to finding food safely.

And as insects, spiders and amphibians were very tasty foods to reptiles, some adapted to this new danger by becoming smaller and hiding in burrows, while others moved higher into the foliage. But upwardly mobile spiders came much later – for now they stayed underground.

Meanwhile, with a lot of violent upheaval and the usual volcanic eruptions and earthquakes, tectonic plate movement had clumped the various landmasses together into one vast landmass extending over the South Pole. Paleontologists call this supercontinent Pangaea (see Title page image for Our Second Age), and the ocean around it the Panthalassa Ocean.

Across Earth coastlines, continental shelves and ocean currents were changed, and all life was disrupted. Because reptiles no longer needed ready access to bodies of water for breeding, some left the dwindling coastlines for river valleys and other inland areas.

Three mountain ranges that had been on separate landmasses, now became one extended range for millions of years. Today they are on separate continents again, as the Appalachian, Caledonian and Scandinavian Mountains.

(Also in the area that is desert in today’s Central Australia, a mighty river was flowing from a towering mountain range. Today this river (the Finke) is little more than a series of billabongs and underground streams; and the mountains (the Macdonnell Ranges) are just an eroded remnant.)

By this time some reptiles, no longer in need of ready access to bodies of water for breeding, had left the dwindling coastlines for river valleys and other inland areas. But now, as gigantic deserts and salt-beds formed away from the rivers and new coasts, the climate there became colder and colder, and drier and drier.

Reptiles in these areas had to cope with very little water as well as widely fluctuating day and night temperatures. Most of them adapted by digging burrows and by slowing down their metabolism.

For millions of years glaciers covered 1/3 of the land in the Southern Hemisphere (including 1/3 of what would be Australia) and all sea levels dropped. Giant horsetails and other early trees started dying out, and there were frequent wildfires.

These were usually sparked by lightning, and then fuelled by the dryness, and also by the many flammable woody plants - alive and dead.

Suddenly in today’s Siberia a volcanic plume from deep in the mantle began to send out huge rivers of black lava, and the eruptions seem to have continued off and on for around 600,000 years. Lava flowed across Pangaea and massive amounts of sulphur dioxide and carbon dioxide gases were released into the atmosphere.

This apparently tipped Earth into its Third Major Mass Extinction, today seen as the most devastating our planet has ever endured. 90% of species disappeared, and it took 50-100 million years for a relatively stable level of biodiversity to emerge.

What’s more most of the survivors only just made it. Even insects were reduced to very few species, whereas today they are our planet’s most prolific and diverse multi-celled animals. There are estimated to be 30-100 million insect species compared with 12,000 species of birds and mammals. How’s that as an example of recovery from a near-death experience?

(The Sydney Basin sandstones that make up the mass of today’s Blue Mountains were laid down around this time. The area that would later be uplifted into a high plateau was part of a vast coastal flood plain extending east beyond today’s Sydney.

(Its rivers rose in colder areas far to the south, and sand was washed down continually with snow-melt from these rivers. As it was deposited on the plain, it slowly built up into layers of sandstone.

(Below the sandstones were layers of coal from forests, formed long before from trees in ancient river deltas. And below the coal were marine shales deposited when the area was covered by an ancient sea.

(Because of later uplifting and erosion the various layers are seen clearly today in Katoomba’s Mount Solitary, which the local Gundungurra people call Korowal.)

* * * * * *
With around 450,000 species,
beetles constitute by far the largest group of insects on Earth.
This collection gives us a glimpse
of the remarkable (and beautiful) diversity of just a few of them.
(another Google image)

OUR SECOND AGE: Scene 1

OUT OF THE WATER

‘You have to step backward, the better to jump forward.’
French proverb

Around 500 million years ago (or ‘Once upon a time’?) while all of Earth’s complex organisms still lived in the water, a few algae clinging to rocks above the low-water mark took the huge evolutionary step that brought plant life onto land.

When exposed by low tides algae quickly dried out and in drought conditions they died. But now some were creating a waxy external layer that enabled them to stay wet on the inside until water covered them again. A few even adapted enough to live in moist conditions rather than in water, evolving into early mosses and liverworts.

By this stage a new kind of beings had emerged, plant-like organisms that do not photosynthesize and live on organic matter (the kingdom of fungi). A few merged with algae to form paler-coloured lichens, in which the algae supplied carbohydrates from photosynthesis, and the fungi supplied extra nourishing minerals.

Microbes played their part in this, for a number had come on land some time before and started breaking rock down into soil. Because it could store rainwater and minerals soil was essential for the first true land-plants to emerge.

Now a few creatures without backbones (invertebrates) began to crawl up and out from riverbeds and seabeds. They included big sea-worms, millipedes, mites and shelled and segmented insects, as well as predators like spiders, which hid under rocks or burrowed into the soil to wait for passing prey much as they had done in the water. But they all had to create ways of breathing, moving and breeding in air rather than in water, and so their various organs and the interaction among them evolved too.

At this stage a few small insects might have begun experimenting with living on the water-surface and even growing light wings.

Soon taller plants, like horsetails (with stiff leaves arranged in whorls) and ferns (with uncoiling fronds), were sending rootlets into the soil after nutrient-rich water. They could store it inside themselves now, pumping it up as sap into their strengthening, lengthening stems, built up from the stubs of fallen fronds or leaves. The taller they grew the more the breezes could help disperse their spores.

Slowly different plants spread from the fertile river deltas and coasts into the interior, and Earth’s barren land-surfaces began to go green. After transforming the water and atmosphere, life was now transforming the land.

But at this point Earth had its First Major Mass Extinction since complex life evolved, apparently associated with a huge ice age. Based on fossil records more than half of the animals on land and in the water seem to have completely disappeared, including many kinds of trilobites.

But what causes ice ages and other devastating climate changes?

The most popular theory today focuses on Earth’s tectonic plates. Their movement not only causes volcanic and earthquake activity, but also re-organizes Earth’s land-masses and oceans. All this leads to recurrent, often quite sudden, climate changes as a tipping-point is reached. And depending on their scale, local or widespread extinctions follow.

However an overwhelming climate change can come about in many ways. Some are triggered by inorganic events such as variations in Earth’s orbit or tilt or asteroid impacts, and some by activities of organisms, such as the release of poisonous oxygen by blue-green bacteria in search of food (see the post of Our First Age, Scene 3).

Earth has had five Major Mass Extinctions, and many minor ones. After each one life has eventually reassembled in more complex and diverse ecosystems than before. In this process more general adaptations such as sexual reproduction are usually carried over, but specific ones such as various kinds of visual perception apparently start all over again.

The transition to a new stability takes millions of years and scientists today have a fair idea how this happens.

As you might expect by now, microbes find it quite easy to adjust and keep on multiplying. Many recycle the bodies of the victims into new life, while others provide food for the survivors. Meanwhile the survivors keep reproducing, with gradual small changes to suit their new environment.

Over time lots of new plants and animals emerge, competing for available niches. If a large plant-eating family goes extinct, another large plant-eating family emerges, and so on.

Eventually the few winners in the transition game form new webs of life in each shared territory – and they keep on consolidating the new ecosystem together, until it is dissolved and replaced in its turn.

So these Major Mass Extinctions are another example of our Universe's system of dynamic balance punctuated by sudden transformational change.

It is as if the web of life on Earth (rather like a star) needs a sudden collapse so that new clumpings can occur. Altogether, as a result of both major and minor mass extinctions, scientists estimate that 99% of all species evolving on Earth are extinct today.

But there is an important difference between a major mass extinction and a star coming to the end of its fusion process.

The extinction event is not predictable, and the survival of any species has little to do with is fitness for life in a local ecosystem. External conditions have intervened, and the only pattern seems to be that species with a wide range of food options and/or a short life-cycle are more likely to survive.

On the other hand Earth’s evolution cannot go on forever. The Sun will exhaust its fuel in 4 or 5 billion years. And long before that, the searing expanding Sun will make it too hot for Earth to support life as we know it. Gaia will begin to die.

As the water evaporates more and more rapidly, evolution will turn back on itself as diversity and complexity decrease. First to go will be animals, then plants and other complex life, then all but the hardiest microbes.

At some time also the Moon will escape from its constantly widening orbit around Earth.

Then as the Sun rapidly expands before its final collapse, the probability is that our planet’s solids will melt or disintegrate, and solids and gases will be dispersed.

We presume that Earth’s energy will be transformed in some way, because scientists tell us that energy cannot be destroyed. And its rocks, dust and gases may become rocks, dust or gases somewhere else.

But perhaps some of the debris will harbour microbes in a dormant form, and they may colonize a moon circling Jupiter or Saturn. The hotter Sun will have thawed the ice there today and enable some to photosynthesize. Then the evolutionary impetus may lead to a new range of co-evolving beings there, surviving and thriving until the sunlight dims.

Earth’s microbes even have a very small chance of reaching a far distant solar system. If they manage to evolve in a very different environment, we can assume that it will be as a very different range of complex beings.

However there is no need for us to worry about all of this. Earth is still in the prime of its life.

Scientists expect that the cycling of major mass extinctions followed by increased biodiversity will continue on our planet for another billion years. That is the same time-frame in which humans evolved from the first multi-celled organisms – soft-bodied, slowly drifting and not yet plants or animals (see the post of Our First Age, Scene 4).

We are already exploring our solar neighbourhood. Surely, at some stage in the future, we will develop the technology needed to find a home in a younger solar system. Or if not us, then whatever species emerges in our place. And the long evolution that began on Earth will have a chance to continue there.

But back in our story, as microbes, plants and animals recovered from the First Major Mass Extinction, they tried many different ways to prosper in a range of new environments – on land, and in the air. By around 400 million years ago, among the early fish diversifying in the oceans there were now many with teeth, including at least one 6-metre long monster of the deep, Dunkleostus terrelli (long extinct) and also the coelacanth (still clinging to life today).

And several smaller species of toothed fish were colonizing tidal areas and shallow rivers. In the process the gill slits of some evolved into a set of lungs, and the bony fins of others into four stubby legs.

(One such creature, Acanthostega gunnari, lived in the area that would become Queensland. It had both gills and lungs and also four legs with digits, which it used in water and on land. Today’s lungfish is a descendant of a species like this.)

Soon, in response to lower water levels, lack of food or more efficient predators, a few walking fish followed invertebrates onto higher ground and evolved into amphibians, living both in water and on land. And the focus of our story narrows to follow them.

It is not too hard to imagine the enormity of the change involved in being one of those animals that emerged from the water, breathing and moving in air for the first time. Because of course we have had a related experience – as a baby emerging from warm security in the amniotic fluid of our mother’s womb.

But in order to manage the change these pioneers had to undergo what scientists call an incomplete metamorphosis, where they developed from eggs laid and fertilized in the water through fishlike young into air-breathing adults walking on dry land. As they spent more time on land they gradually evolved.

In due time they had a neck, a strengthened backbone, more agile limbs, a water-retentive skin, and a stronger, more efficient heart. And their brain developed accordingly: managing their breathing, helping them stand up to gravity, and improving their vision and hearing.

It also developed areas to handle dominance and submission postures, which they could use in encounters with a competing amphibian or a predator to avoid conflict.

But they didn’t yet have the ability to regulate their body temperature, and so they were active in the day, and slept at night.

* * * * * *
Diagram of the Five Major Mass Extinctions on Earth

showing how all except the Third (the most devastating one yet)
were followed by increasing diversity
(another Google Image)

OUR SECOND AGE: Title Page & Song

EARLY DAYS

Earth’s lands and seas 300-240 million years ago

Earth’s lands and seas today

‘With . . . shining morning face’
As You Like It, II, vii, 146




‘We [scientists] should make things as simple as possible,
but not simpler.’
Albert Einstein

This song is by Cole Porter, and I’m sure it is familiar to you. I’ve chosen it for Our Second Age because this is when intimate sexual reproduction came into its own. But, as Cole Porter and many others have done before me, I’ve changed quite a few words to suit the occasion.

LET’S DO IT (LET’S FALL IN LOVE)

When the little Bluebird, who has never said a word,
Starts to sing: ‘Spring, Spring;’
When the little Blue-bell, in the bottom of the dell,
Starts to ring: ’Ding, ding;’
When the little blue clerk, in the office car-park,
Starts a tune to the moon up above,
It is nature, that’s all, simply telling us to fall in love
And that’s why . . .

Birds do it, bees do it,
- Flying foxes, frogs and fleas do it,
Let’s do it, let’s fall in love.

The upper sets in their jets do it,
- Corny barbershop quartets do it,
Let’s do it, let’s fall in love.

In Kakadu crocodiles do it,
Then they lie in the sun.
Cats on the tiles do it.
It doesn’t sound like much fun.

Young kids in jeans without means do it,
People say in Boston even beans do it,
Let’s do it, let’s fall in love.

Termites take off and fly to do it,
- Most male spiders die to do it,
Let’s do it, let’s fall in love.

Selected cells in a petrie dish do it,
- Even drifting jellyfish do it,
Let’s do it, let’s fall in love.

The lovely rose opens up to do it,
She doesn’t care who drops in.
Celebrities attend the Melbourne Cup to do it,
They don’t think it’s a sin.

When they get the call, Earthlings all do it,
Overweight(1) and skinny(2), short(3) and tall(4) do it,
(big finish) Let’s do it, let’s fall in love!
(sexy whisper) Let’s do it.

NB A dash (-) indicates a rest on the first beat (I tap my foot).

1. (overweight)
elephant seals

3. (short)
cane toad











2. (skinny)

male stick insect
and larger female

4. (tall)
Eucalyptus regnans

(click on each image to enlarge)

* * * * * * *

OUR FIRST AGE: Scene 5

THE FIRST PLANTS AND ANIMALS

‘One exercises justice or injustice to plants and animals as well.
Plants and animals also have a right to unfolding and self-realization.
They have the right to live.’
Arne Naess

Around 550 million years ago, after a 200-million-year period when ice covered a large proportion of Earth’s surface (an Ice Age), multi-celled beings, still in the water but now in significantly different shapes and sizes, took a huge step. They diverged into what biologists call the kingdoms of plants (technically still algae at this time) and animals.

Experts don’t know how it happened, but early tube-like polyps provide examples of transitional species because, judging from their direct descendants today, they must have behaved like plants at one stage and animals at a later stage.

While immature these descendants attach their bottom end to a rock or another polyp, and at their top end catch food by means of a flowery circle of tentacles around their mouth.

Then at maturity they produce cloned offspring in the form of buds. In species like anemones and corals these stay attached to the parent. But in species like jellyfish the buds break off, hang their tentacles down, and drift until male and female cells unite to make flatter, flabby offspring that can move purposefully. These then swim off in search of a rock or another polyp that they can settle on, and the cycle begins again.

Experts also don’t know how kingdoms branched into the progressively narrower classifications used to structure what we call The Tree of Life, based on kingdoms, phyla (or divisions), classes, orders, families, genera, species and races. (You may remember this as “Kings Play Chess On Fat Green Stools".)

However there is growing evidence that great diversifications happen quickly in evolution - in response to a crisis, or tipping point, of some kind.

The main differences between the plant and animal kingdoms are found in their cell structure and their sources of energy.

Plants and algae have hard-walled cells containing chloroplasts that make food by photosynthesis, and they also gain several trace nutrients by absorbing various minerals dissolved in water. Animals on the other hand have soft-walled cells with no chloroplasts to make food, and so their energy comes from plants. They also need the oxygen released by photosynthesis in order to breathe. Therefore plants are absolutely essential for them.

But neither animals nor plants can live without microbes. Oxygen-avoiding (anaerobic) microbes live in an animal’s stomach, breaking up what it eats into a form that it can absorb or excrete. And oxygen-tolerant (aerobic) microbes break up the waste that an animal excretes into water-soluble elements that plants can absorb.

So back in our story, life on Earth now had a way of being that involved interdependence among very diverse beings. Their vital needs were inextricably intertwined.

From this point microbes, plants and animals have all been integral parts of a complex local web of life, evolving together as they compete for available resources and avoid conflict by settling into separate niches.

By concentrating on certain locations or on certain kinds of food they learn to adjust their boundaries. By feeding on weaker individuals, new growth and infants they restrict but also assist each other’s progress, ensuring that the fittest members of each plant and animal species are the most likely to live to maturity and then reproduce.

Today’s scientists see each being as having a chance to thrive within the environment that it is helping to create. So their focus is on co-evolution rather than evolution, ecosystems rather than habitat, and ecology rather than biology. In this approach, since each species has evolved by learning through feedback loops how far its self-interest extends in its ecosystem, no one way of being can be seen as dominant.

Of course as yet in our story there were only aquatic ecosystems. But they ranged from surface areas, where most animals ate living algae, to ocean floor or riverbed areas, where most animals scavenged for algal or animal remains in sandy sediments built up by microbes that separated minerals out from the water.

And we have at last entered the realm of organisms visible to the naked human eye. From now on we will concentrate on their development.

As plant and animal populations both exploded, another evolutionary step occurred.

A few animals began preying on their fellows rather than eating plants or scavenging. An animal species’ way of being from now on would involve survival by eating plants and/or other animals.

And since animal-eaters have to pursue, catch and then kill for their food, and prey animals have to avoid predators and/or fight for their life, they all need more creative attentiveness and more complex organization than plants do.

So nerve and muscle tissues developed, with the nerves sensing an internal or external signal, and the muscles responding appropriately. At first this involved an automatic (or instinctive) pattern of behaviour. In response to a "possible food" signal an animal moved towards it (the forerunner of pleasure), and in response to a "possible danger of becoming food" signal it moved away (the forerunner of pain). But eventually it would lead to active awareness of sensation (sometimes called sentience).

Now many plants and animals were also growing larger as they competed for an ecological niche. A few were beginning to use colour to attract or warn others, while others were making use of the excess calcium that they took in from the water.

Thus on the ocean floor some polyps were using excess calcium to make protective shelters. With the help of microbes that deposited carbon the shelters slowly built up as coral reefs, which today are one of Earth’s most productive ecosystems. One of them (Queensland’s Great Barrier Reef) is the biggest structure that animals, including humans, have ever made.

In other animals the instruction to excrete calcium somehow changed to an instruction to make a protective sheath on their soft body. When an exterior skeleton and jointed legs eventually formed and the animal survived and reproduced successfully, this led to a new division (or phylum) of animals: arthropods. They included the now extinct trilobites.

All these animals had to shed their old skin before they could grow larger and make a new exo-skeleton. And this is still true for their descendants today. But a few soft animals in another animal division: mollusks, were creating either coiled or cone-shaped shells of calcium that grew with them.

To enhance their attentiveness even further some scavengers developed spots sensitive to light (forerunners of eyes), and some swimmers became sensitive to vibrations through their gills (forerunners of ears). To enhance responsiveness, particularly in the challenging ecosystem near the surface, some developed a central nervous system: another fractal arrangement that picked up signals from various nerves and relayed them to a central processing organ, the brain.

This led to the division of chordates, and then over time a few chordates started depositing calcium inside their bodies to protect their brains and central nervous systems (skulls and backbones). This gave rise to vertebrates, some of which later used calcium to develop jaws for grasping prey more easily.

The asymmetry of immobile sponges compared with the radial symmetry of slow-drifting jellyfish and then the bilateral symmetry of swiftly swimming fish demonstrates how these changes enhanced evolution. In each case the changes helped the animals concerned to find a more secure niche in the now teeming web of life.

And within that web of life microscopic organisms were also diversifying, using silica rather than calcium to make structural improvements. Today this diversity is seen in the micro-plankton that include beautiful diatoms near the surface of the ocean.

And so in several aquatic ecosystems within Earth’s salt waters and fresh waters, plants and animals developed extremely diverse ways of living, including different kinds of asexual and sexual reproduction.

But male and female animal cells were still ejected into the water en masse, with only some managing to pair off. Each resulting egg contained instructions so that the hatchling could develop independently of its parents – but only if it was one of the few that survived infancy. This method of generational transfer is still widespread in aquatic ecosystems today.

Meanwhile tectonic plate movement, driven by activity deep within our planet, had created the huge supercontinent Gondwana and several lesser landmasses. And there were some cosmic players beyond Earth that hadn’t yet made their presence felt.

* * * * * * *

(courses.bio.psu.edu)

Photosynthetic diatoms are very important from a global perspective,
being responsible for perhaps 20% of annual global carbon fixation.
They are encased in a glass-like silica shell, invisible to the naked eye,
and are exceptionally beautiful structures.
Each one consists of two components that fit together, like the bottom and lid of a pillbox.
After the death of individual diatoms,
their microscopic shells sink and gradually form thick layers of sediment (diatomaceous earth).
Living diatoms avoid sinking by regulating their cellular ion concentrations.
(Another Google image)



I intend to post one Age each month until December,
and then the Epilogue and Two-Page Timeline in January.
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