OUR PLANET
‘This grand show is eternal.
It is always sunrise somewhere:
the dew is never all dried at once,
a shower is forever falling, vapour is ever rising.
Eternal sunrise, eternal sunset, eternal dawn and gloaming,
on sea and continents and islands,
each in its turn, as the round earth rolls.’
John Muir
Once we turn our attention from our Universe as a whole to our planet within it we are on firmer, but not completely firm ground – as you will see.
This part of the story begins 5 billion years ago, when a supernova apparently exploded in the Orion Arm of our Milky Way Galaxy, about 2/3 of the way from its centre. Within 500 million years our solar system had emerged from a swirling disc of elements and compounds. Virtually all of its mass was contained in its star, our Sun - about 30% dimmer and cooler than it is today, but the general features of the system were the same as they are today.
Around the Sun orbit eight almost spherical but otherwise quite diverse planets: four rocky ones (in order from the Sun: Mercury, Venus, Earth and Mars) and four much larger gaseous ones (Jupiter, Saturn, Uranus and Neptune). Between Mars and Jupiter is the asteroid belt, a ring of less substantial rocks with varying diameters - from pebble to city-size. There are also many solitary asteroids at various distances from the Sun, and at least two far-flung dwarf planets, including recently demoted Pluto.
But by far the largest component of our solar system is a vast area of dust, gases, and supersonic solar winds. The planets capture only a tiny fraction of the Sun’s waves of electromagnetic energy. The rest radiates out through the solar system, being steadily diluted until it passes through two gigantic rings of smaller bodies and finally disperses out in space. It takes two years for it to get to the outermost reaches of the system.
At that distance the Sun’s gravity has very little force, and its heat and light virtually none, so any bodies there are dark and icy, and orbit very slowly. They are generally a few kilometres in diameter and include some that we call comets – they have an elongated orbit that passes close to the Sun. As a larger comet draws near the inner solar system, it loses frozen gases and debris in a huge sphere and tail of light. And long before it returns to the outer zones it has frozen again, creating its own individual comet-scape on the way.
Solitary asteroids and comets gain momentum as they near the Sun, or as they pass near a planet and are pulled in by its gravity. The giant planet in the fifth orbit pulls many comets and asteroids in, long before they reach the inner solar system. This is Jupiter, 1300 times bigger than Earth, and sometimes called a failed star – it is made up of condensed heated hydrogen and helium, but it is not large or hot enough to ignite.
At this early stage in our story our infant planet was very different from the Earth we know today. It was a molten spheroid, spinning rapidly, wobbling violently on its tilted axis, and half the size it would be when life emerged.
As it cooled, its various elements and compounds formed three basic solid layers: a dense, magnetic and radio-active core, hotter than the Sun’s surface and made up of Earth’s two heaviest metals, iron and nickel; a thick, very hot mantle, some of it slowly moving like tar and made up of silicon, oxygen, iron and sulphur compounds; and a thin, floating and hardening crust made up of the lighter of these compounds. There was also an atmosphere: a fourth gaseous layer held in place by Earth’s gravity and so dense near the surface and diffusing into space. It was made up mostly of nitrogen but also contained water vapour, carbon dioxide and methane, all of which absorbed a lot of the planet’s radiant heat and so slowed down the cooling process.
(The Pilbara in Western Australia has one of the oldest sections of Earth’s crust.)
Pressure in various hotter spots within the mantle sent volcanic plumes of its lighter contents out into the atmosphere - mainly steam, sulphur and carbon dioxide (molecules of carbon and oxygen combined). The heavier contents flowed or floated down to the ground as lava and ash, cooling to form new rock. Over time the crust thickened and virtually covered the surface, in what geologists call tectonic plates. Since then the mantle’s leisurely turmoil has kept them continually splitting and rejoining as they move in different directions, at an average of a few centimetres a year.
When an area of crust was pulled apart lava squeezed through the fissures, and rift valleys formed between the two sections, very slowly but with the occasional huge jerk of a massive earthquake or volcanic eruption. When two areas collided, the leading edge of one was forced down into the mantle creating a deep trough, and high mountains were forced up on the other, again very slowly but also with occasional huge jerks.
Meanwhile large asteroids and comets battered Earth constantly, bringing vital elements and compounds such as water and amino acids, leaving craters all over the surface, and increasing the planet’s size bit by bit. All this time huge dry electrical storms raged high in the atmosphere.
As the planet kept cooling, acid steam from the volcanoes began forming clouds about 15 km up. Acid showers, a mixture of oxygen, hydrogen and sulphur, began to fall and then finally torrential rain with less sulphur. The surging water eroded the mountains, created gullies, and filled craters, depressions and trenches.
Warm pools, seas and oceans slowly formed, ‘salted’ with water-soluble elements and compounds like iron, calcium, phosphates and sodium chloride. Most ended up in the ocean, leaving higher areas exposed as various islands and continents. These were quite different from those of today, and so were the first shallow continental shelves, steep continental slopes and deep trenches around them. The planet now had a fifth layer: liquid water. Today the crust’s thickness averages 30 km in continental areas and 8 km under the ocean.
(In Western Australia we have the oldest recorded evidence of water on Earth. These are grains of zircon, formed by the interaction of water, silicon and the metal zirconium around 4.3 billion years ago.)
At this early stage, while our planet was apparently rotating once every 8-10 hours, a huge asteroid gave it a glancing blow that sent great fragments of rock up into space. Earth’s gravity kept them in a close orbit as they clumped into a rotating Moon, 1/80 the mass of the planet. And now the opposing pull of the Moon’s gravity, particularly on the ocean, began to help slow the planet’s spin and wobble.
At first the Moon was probably ten times larger than the Sun in Earth’s sky, and when it was between them the sky darkened over a huge area for hours. But its orbit has very slowly widened. Since long before humans emerged it has seemed about the same size as the Sun, blotting out its light for a few minutes in a solar eclipse that occurs once or twice a year, along a different narrow path each time. In 500 million years the Moon will be no more than a large silhouette as it passes in front of a still brightly shining Sun.
The Moon’s rotation has slowed too. Ever since humans have been looking at it, it has kept the same general face towards Earth, taking the same time to rotate as it does to complete its orbit. Its phases occur because we see only the part of this face that is lit up by the Sun – to the naked eye the unlit part has virtually disappeared, except sometimes in its crescent phase when it is lit by reflected Sunlight on Earth, a phenomenon called Earthshine.
Each of the giant outer planets in our solar system has several moons today, all relatively much smaller than our Moon; and some have rings or partial rings of smaller satellites again. Scientists don’t know how these diverse planetary systems formed, but as in a solar system each seems held in a balance between clumping and splitting apart.
Back in our story, while the Moon was helping to stabilize Earth and slow its rotation our solar system was stabilizing too. Asteroid and comet impacts were lessening and Earth’s iron core had by now set up a magnetic shield in the atmosphere. This protected our planet from cosmic radiation (which would otherwise destroy any future life) and from solar winds (which would otherwise blow away much of the atmosphere).
Earth was also just the right size, in just the right orbit, for most of its water to remain a liquid rather than a gas or a solid. This was essential for life to emerge because the Sun’s searing ultra-violet rays at this stage made the land-surfaces uninhabitable. From the time of Earth’s first ‘live’ molecules, all of its organisms would associate easily in a watery habitat. And later, when some came onto land, they would be largely made of water.
Today the ocean covers 72% of our planet’s surface, and holds 97% of its water. Away from the continents, its average depth is 4 km, except where tectonic plate movement has created sea-mounts. Near the continents the deepest trench is on the western rim of the Pacific Ocean, where the Pacific Ocean Plate is being pushed under the Philippines Plate. This is the Mariana Trench, at its deepest point 11 km below the surface - 2 km deeper than Mount Everest is high!
We now know that from a viewpoint between Earth and the Moon, the refraction of light from the ocean and the water in the atmosphere makes our planet a distinctive blue colour. We also know that the tiny proportion of our water that is fresh keeps cycling through ice, liquid and vapour, helping to drive the way that life on Earth works.
For these reasons Lynn Margulis has suggested that our planet could be more fittingly called ‘Water’. If it made us all more aware of the importance of our water cycle, perhaps a new name would be a good idea. What do you think?
This part of the story begins 5 billion years ago, when a supernova apparently exploded in the Orion Arm of our Milky Way Galaxy, about 2/3 of the way from its centre. Within 500 million years our solar system had emerged from a swirling disc of elements and compounds. Virtually all of its mass was contained in its star, our Sun - about 30% dimmer and cooler than it is today, but the general features of the system were the same as they are today.
Around the Sun orbit eight almost spherical but otherwise quite diverse planets: four rocky ones (in order from the Sun: Mercury, Venus, Earth and Mars) and four much larger gaseous ones (Jupiter, Saturn, Uranus and Neptune). Between Mars and Jupiter is the asteroid belt, a ring of less substantial rocks with varying diameters - from pebble to city-size. There are also many solitary asteroids at various distances from the Sun, and at least two far-flung dwarf planets, including recently demoted Pluto.
But by far the largest component of our solar system is a vast area of dust, gases, and supersonic solar winds. The planets capture only a tiny fraction of the Sun’s waves of electromagnetic energy. The rest radiates out through the solar system, being steadily diluted until it passes through two gigantic rings of smaller bodies and finally disperses out in space. It takes two years for it to get to the outermost reaches of the system.
At that distance the Sun’s gravity has very little force, and its heat and light virtually none, so any bodies there are dark and icy, and orbit very slowly. They are generally a few kilometres in diameter and include some that we call comets – they have an elongated orbit that passes close to the Sun. As a larger comet draws near the inner solar system, it loses frozen gases and debris in a huge sphere and tail of light. And long before it returns to the outer zones it has frozen again, creating its own individual comet-scape on the way.
Solitary asteroids and comets gain momentum as they near the Sun, or as they pass near a planet and are pulled in by its gravity. The giant planet in the fifth orbit pulls many comets and asteroids in, long before they reach the inner solar system. This is Jupiter, 1300 times bigger than Earth, and sometimes called a failed star – it is made up of condensed heated hydrogen and helium, but it is not large or hot enough to ignite.
At this early stage in our story our infant planet was very different from the Earth we know today. It was a molten spheroid, spinning rapidly, wobbling violently on its tilted axis, and half the size it would be when life emerged.
As it cooled, its various elements and compounds formed three basic solid layers: a dense, magnetic and radio-active core, hotter than the Sun’s surface and made up of Earth’s two heaviest metals, iron and nickel; a thick, very hot mantle, some of it slowly moving like tar and made up of silicon, oxygen, iron and sulphur compounds; and a thin, floating and hardening crust made up of the lighter of these compounds. There was also an atmosphere: a fourth gaseous layer held in place by Earth’s gravity and so dense near the surface and diffusing into space. It was made up mostly of nitrogen but also contained water vapour, carbon dioxide and methane, all of which absorbed a lot of the planet’s radiant heat and so slowed down the cooling process.
(The Pilbara in Western Australia has one of the oldest sections of Earth’s crust.)
Pressure in various hotter spots within the mantle sent volcanic plumes of its lighter contents out into the atmosphere - mainly steam, sulphur and carbon dioxide (molecules of carbon and oxygen combined). The heavier contents flowed or floated down to the ground as lava and ash, cooling to form new rock. Over time the crust thickened and virtually covered the surface, in what geologists call tectonic plates. Since then the mantle’s leisurely turmoil has kept them continually splitting and rejoining as they move in different directions, at an average of a few centimetres a year.
When an area of crust was pulled apart lava squeezed through the fissures, and rift valleys formed between the two sections, very slowly but with the occasional huge jerk of a massive earthquake or volcanic eruption. When two areas collided, the leading edge of one was forced down into the mantle creating a deep trough, and high mountains were forced up on the other, again very slowly but also with occasional huge jerks.
Meanwhile large asteroids and comets battered Earth constantly, bringing vital elements and compounds such as water and amino acids, leaving craters all over the surface, and increasing the planet’s size bit by bit. All this time huge dry electrical storms raged high in the atmosphere.
As the planet kept cooling, acid steam from the volcanoes began forming clouds about 15 km up. Acid showers, a mixture of oxygen, hydrogen and sulphur, began to fall and then finally torrential rain with less sulphur. The surging water eroded the mountains, created gullies, and filled craters, depressions and trenches.
Warm pools, seas and oceans slowly formed, ‘salted’ with water-soluble elements and compounds like iron, calcium, phosphates and sodium chloride. Most ended up in the ocean, leaving higher areas exposed as various islands and continents. These were quite different from those of today, and so were the first shallow continental shelves, steep continental slopes and deep trenches around them. The planet now had a fifth layer: liquid water. Today the crust’s thickness averages 30 km in continental areas and 8 km under the ocean.
(In Western Australia we have the oldest recorded evidence of water on Earth. These are grains of zircon, formed by the interaction of water, silicon and the metal zirconium around 4.3 billion years ago.)
At this early stage, while our planet was apparently rotating once every 8-10 hours, a huge asteroid gave it a glancing blow that sent great fragments of rock up into space. Earth’s gravity kept them in a close orbit as they clumped into a rotating Moon, 1/80 the mass of the planet. And now the opposing pull of the Moon’s gravity, particularly on the ocean, began to help slow the planet’s spin and wobble.
At first the Moon was probably ten times larger than the Sun in Earth’s sky, and when it was between them the sky darkened over a huge area for hours. But its orbit has very slowly widened. Since long before humans emerged it has seemed about the same size as the Sun, blotting out its light for a few minutes in a solar eclipse that occurs once or twice a year, along a different narrow path each time. In 500 million years the Moon will be no more than a large silhouette as it passes in front of a still brightly shining Sun.
The Moon’s rotation has slowed too. Ever since humans have been looking at it, it has kept the same general face towards Earth, taking the same time to rotate as it does to complete its orbit. Its phases occur because we see only the part of this face that is lit up by the Sun – to the naked eye the unlit part has virtually disappeared, except sometimes in its crescent phase when it is lit by reflected Sunlight on Earth, a phenomenon called Earthshine.
Each of the giant outer planets in our solar system has several moons today, all relatively much smaller than our Moon; and some have rings or partial rings of smaller satellites again. Scientists don’t know how these diverse planetary systems formed, but as in a solar system each seems held in a balance between clumping and splitting apart.
Back in our story, while the Moon was helping to stabilize Earth and slow its rotation our solar system was stabilizing too. Asteroid and comet impacts were lessening and Earth’s iron core had by now set up a magnetic shield in the atmosphere. This protected our planet from cosmic radiation (which would otherwise destroy any future life) and from solar winds (which would otherwise blow away much of the atmosphere).
Earth was also just the right size, in just the right orbit, for most of its water to remain a liquid rather than a gas or a solid. This was essential for life to emerge because the Sun’s searing ultra-violet rays at this stage made the land-surfaces uninhabitable. From the time of Earth’s first ‘live’ molecules, all of its organisms would associate easily in a watery habitat. And later, when some came onto land, they would be largely made of water.
Today the ocean covers 72% of our planet’s surface, and holds 97% of its water. Away from the continents, its average depth is 4 km, except where tectonic plate movement has created sea-mounts. Near the continents the deepest trench is on the western rim of the Pacific Ocean, where the Pacific Ocean Plate is being pushed under the Philippines Plate. This is the Mariana Trench, at its deepest point 11 km below the surface - 2 km deeper than Mount Everest is high!
We now know that from a viewpoint between Earth and the Moon, the refraction of light from the ocean and the water in the atmosphere makes our planet a distinctive blue colour. We also know that the tiny proportion of our water that is fresh keeps cycling through ice, liquid and vapour, helping to drive the way that life on Earth works.
For these reasons Lynn Margulis has suggested that our planet could be more fittingly called ‘Water’. If it made us all more aware of the importance of our water cycle, perhaps a new name would be a good idea. What do you think?
* * * * * * *
Earth and Moon today
from a point in space where they both appear slightly "gibbous",
i.e the observable illuminated part is greater than a semicircle
and less than a circle.
(image authorized for non-commercial use
under a Creative Commons Licence -
just one of the many available through Google Images)
Earth and Moon today
from a point in space where they both appear slightly "gibbous",
i.e the observable illuminated part is greater than a semicircle
and less than a circle.
(image authorized for non-commercial use
under a Creative Commons Licence -
just one of the many available through Google Images)
I intend to post the five scenes of Our First Age throughout June,
and then one Age each month until December.
That means that the Epilogue and Two-Page Timeline will be posted in January.
If you would rather have a free email copy of the book, please sign in to my Guestbook
(see first post: An Introduction),
making sure that you ask for your entry to be kept private.
and then one Age each month until December.
That means that the Epilogue and Two-Page Timeline will be posted in January.
If you would rather have a free email copy of the book, please sign in to my Guestbook
(see first post: An Introduction),
making sure that you ask for your entry to be kept private.
1 comment:
Your images are fantastic. Thankyou for what must have been a lot of research
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