Everything that has ever been built, or grown, or made on Earth by humans has been there since its formation.
During the birth of the Solar System, Earth was one of four rocky planets that formed. Due to the incredible pressure and gravity of the protostar at the centre, heavy elements smashed together and began to form protoplanets.
The lighter elements, such as hydrogen and helium, that weren’t brought into the protostar, were blasted away by a constant solar wind; charged particles launched from the star. This left only the heavy elements, which as mentioned, coalesced into dense, rocky planetary bodies.
But before we go any further, let’s have a look at the structure of the Earth, as it currently is.
As you can see in the figure above, the Earth is stratified into distinct layers, but it was Earth’s core that formed first.
Heavy elements, pulled together by gravity, condensed into a glowing, molten body that was constantly bombarded by asteroids during its early stages of development. As more material slammed into the protoearth, drawn by the ever-increasing gravitational pull, the outer layers began to cool as they heavier elements sank towards the core and the lighter elements remained near the surface.
It is Earth’s core and its spin that is responsible for protecting us from the constant solar wind that the Sun throws towards us every day. The heavy molten nickel-iron core and its rotation create a magnetic field that essentially acts like a forcefield and doesn’t allow harmful radiation to strike the planets surface.
While the Earths layers had taken shape, there were still an incredible number of asteroids and objects bombarding it. It was around this point in its evolution that the Earth is theorised to have been hit by another protoplanet (roughly the size of Mars). This impact blasted chunks of the Earths mantle into space forming the Moon. However, that is another topic and will be a whole other post itself.
But this bombardment of asteroids was fortuitous, as it is currently thought that these asteroids were the primary way that water was delivered to Earth.
As the molten, extremely hot protoearth began to cool, the gases emanating from the planets surface formed, at first a rather inhospitable atmosphere.
It would take millions of years for oceans of ammonia to become oceans that resemble the ones we have today, and even longer for the very first forms of life, photosynthesizing organisms that expelled oxygen into the atmosphere, to come about.
But it isn’t only an atmosphere we have to thank for life being able to evolve on Earth. There is a point in space, a certain distance for every star, called the Goldilocks Zone. Not too hot, not too cold, just right. Earth is within this Zone, and it is believed that for life to exist on any planet, it too needs to be in the Goldilocks zone, as this is the area in which water can exist (and it is currently thought that life requires water).
Earth is lucky. And we are lucky.
In the chaos that was the early Solar System the evolution of Earth could have gone one of a million different ways, and yet, here we are.
As the planet cooled under the calming eye of the yellow Sun, life evolved, and it still is evolving, even now.
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