Planet Earth is the most amazing place in the universe. It is the only planet that we know of upon which all manner of life has evolved to colonise every conceivable corner, on land, in the sea and even in the air. Ever since one particular species became aware of itself, and able to think, explore and question our place in the cosmos, there has been one massive question: “How did all this get here?”
In one of the spiral arms of our galaxy, one of the long tendrils of stars that coil outwards from the galactic centre, a momentous event took place over 4.6 Billion years ago. A massive, rotating cloud of gas and dust was collapsing under its own gravity, heating up as it was pulled tighter and tighter together into a flat disk, over a billion miles in diameter. At the centre of that disk, the temperature and pressure from the rapidly collapsing gas became intense enough that atoms of Hydrogen began to fuse together to create helium. In that single moment, our Sun began to shine. Though events like this happen all the time in the cosmos, this one was particularly significant to us. For 96 million miles away from the newly burning sun, more dust began to clump together, creating larger and larger clumps. The gravity of these clumps attracted still more dust, and over the millennia they increased in size. Millions of years later, and what had started from tiny rocks and particles of dust was now a red hot ball of rock, rivers of molten lava running across its surface, and 8,000 miles diameter. Though it would be unrecognizable to modern eyes, our Earth was beginning to take shape.
But Earth was not alone in her orbit around our sun, which was already millions of years old. Another planet called Theia, had also formed 96 million miles from the sun, and shared an orbit with that of our Earth. For about 30 million years after Earth and Theia were formed, they orbited without too much interference with each other. But when Theia had collected enough of the remaining dust cloud to be about 10% the mass of the Earth, gravitational interactions between the two planets destabilised Theia’s orbit. Theia smashed into Earth in a colossal impact, throwing millions of tons of rock into orbit round our planet. Theia was utterly destroyed, but the Earth’s molten surface swiftly healed the impact scars. Yet Earth would still not be alone: the rocky debris around Earth clumped together, much as Earth had done herself. This formed the moon, and has been our constant companion for over 4 billion years.
Earth’s turbulent past was drawing to a close. An event known as the Late Heavy Bombardment, a few hundred million years after the formation of the Moon, saw Earth and her companion Moon subjected to a massive interplanetary siege from asteroids and comets. Yet is also believed to have delivered masses of water to Earth in the form of comets, enormous ‘Dirty Snowballs’ of ice and frozen dust that hurtle through space. It was this water that eventually formed the oceans, in which simple, primordial life began to emerge, life that would eventually arise to ponder the question: “How did this all get here?”
