The Story of the Universe and Me: Where Did I Come From?
Part 3: The Earth
The Earth formed in the same manner as its brethren: by accretion from the disk of dust left behind by the sun’s birth. Heated by the many collisions that grew it, the planet was molten at first. The heavier material, iron in particular, was drawn to the centre of the new body, forming a swiftly spinning metallic core suspended in a pocket of magma. This huge, spinning, conductive ball at the planet’s heart was enough to create a strong magnetic field around it, something which we would thank it for later. The differentiation by mass left the planet a layered thing, with a solid inner core, a liquid outer core, a mostly solid but, over the lifespan of a planet, ever-shifting mantle, and, eventually, as the heat from its birth gradually leaked into space, a hard crust on its surface. This crust was briefly interrupted by the arrival of the Moon, as described previously, but soon repaired itself.
The young planet remained covered in volcanism and continued to be bombarded by the chaos of the solar system’s development. The first continents began to form, sections of crust that could move around and grind against each other, propelled by the ponderous motions of the mantle below. The Earth was coated in a blanket of greenhouse gases and volatiles belched out by the volcanoes and great collisions. Also present was an abundance of a certain covalent molecule known as water, most likely delivered to the planet by ice-rich comets and asteroids. The planet eventually cooled enough for this water to form clouds and take liquid form, falling to the surface as rain. It pooled into vast oceans, even then covering the vast majority of the surface.
Within these oceans, a fortunate conjunction of elements was taking place. The hydrogen and oxygen in the water was combining with carbon from the air into organic molecules; these molecules formed greater units, turning into polymers, which in turn joined into longer chains called proteins. These chains banded together to form increasingly complex systems, and, with the help of other complex organic molecules like RNA and DNA, developed into the first signs of life.
To be continued!