circa 4,540,000,000 BCE — The Earth gets cooler

In the early millenia of what is sometimes referred to as the Hadean era of the Earth, there were no rocks as we would commonly understand the term – it was too hot for them to form. Still, the Earth was slowly cooling and solidifying. It’s worth noting that the Sun itself was not as hot at this time – like the larger planets of our solar system, it was still accreting matter to itself. Rockballs like the Earth (and Mars and Venus) were largely done with this process (although the occasional meteor or cometary impacts still occurred).

By the end of this era, approximately 3,800,000,000 years ago, the Earth had cooled sufficiently to allow for the stable formation of rocks, and its surface had begun to split into tectonic plates. Most importantly for humanity’s future, life had begun: the earliest evidence of photosynthesis dates from around this time.