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Evolving Earth

A series of four disks – illustrations of how Earth might have looked from afar at different epochs – starts on the right with a red and brown molten world just after formation, a cooling Earth with oceans and continents 4.3 billion years ago, a possibly green-tinged Earth inhabited by the earliest life 3.7 billion years ago, and Earth today, blue, green, and white, with oceans, continents, and ice caps.First disk:Earth FormsOur world accreted from a Sun-circling disk of gas and dust about 4.5 billion years ago – then collided with a Mars-sized body about 50 million years later, leading to formation of the Moon.Second disk:Earth CoolsThe surface cooled rapidly, achieving a hot but solid crust, with early oceans and impact basins filled with lava by about 4.3 billion years ago.Third disk:Life BeginsThe earliest life-forms might have appeared during the archean Era some 3.7 billion years ago – or even earlier. Oceans could have been tinged green by iron ions. Life-forms relying on oxygen, and an oxygenated atmosphere, did not arise until much later.Fourth disk:Earth TodayOur world of abundant life, with its oxygen-rich atmosphere, likely would be recognized as habitable from many light-years away. But the presence of oxygen might not have been detectable even as recently as 800-500 million years ago.
June 13, 2023

Our planet passed through vastly different stages on its way to becoming a habitable world.