#Resource The Geologic timeline https://podcasts.apple.com/podcast/id385427377?i=1000745514671&r=588&t=588 “interesting that, less than 10% of the history of the Earth, in which we, Earth looks anything like we imagine it today with plants and animals and greenery and all of this stuff. None of that would have existed before then. ## prokaryotic life is bacterial life. Eukaryotic life have much more complex internal cellular machinery “in the oceans, then the shallow oceans, and early in the Earth's formation. Now, for the next 2 billion years even longer, 2 to 2.5 billion years, the only life that existed on Earth was bacterial life or archaea and bacterial life. no macroscopic life. there were mats of bacteria that existed, they would grow over a surface, and these fossilized, now called stromatolites, these are sort of fossilized mats of bacteria. So they could be macroscopic in that sense, but that's just because there's many bacteria growing on a surface or growing near each other and forming a sort of a film that covers the surface and is identifiable. But that's not a single organism, and there's no specialization of tissue of cells into different tissues or anything like that. “So we're still talking about individual microscopic organisms, and they were all the life that existed on Earth for at least the first two billion years. That's definitely into the protozoic eon, and it may have even been longer than that, but it's not really known when eukaryotic life first developed. Remember, prokaryotic life is essentially bacterial life. They're much smaller and simpler. Eukaryotic life are larger cells, or many of them are larger and have much more complex internal cellular machinery. It's thought that eukaryotic life probably originated around the time of the Great Oxidation Event or slightly afterwards. They didn't cause the Great Oxidation Event. Remember, that was about 2.5 billion years ago. That was caused by photosynthetic bacteria that were pumping out more and more oxygen.” From The Science of Everything Podcast: Episode 157: The Geologic Time Scale, 17 Jan 2026 https://podcasts.apple.com/gb/podcast/the-science-of-everything-podcast/id385427377?i=1000745514671&r=988 This material may be protected by copyright. ## Time overview “So don't worry if you don't pick it up on the first go-through. So you'll recall that the longest unit of geochronology is the eon, and there's exactly four of those. So let's go through the four eons again. So the first is the Hadian eon. So that began with the formation of Earth about 4.6 billion years ago, and it ends with the earliest known rock formations, roughly about four billion years ago. So this is the early time of, like, after the formation of Earth, but there's still a lot of changes happening in terms of the Earth's composition of the atmosphere and with the differentiation of the internal layers of Earth and asteroid bombardments and things like that. So it's a very high energy. Life is thought to have emerged just at the end of the Hadean eon. So the next eon is the Archaeon, and that lasts from 4 to 2.5 billion years ago. It begins with the formation of the first rocks, as I mentioned, and it ends 2.5 billion years ago. So I've not actually been able to find a very clear reason as to why the Archaeon ends at 2.5 billion years[…]” From The Science of Everything Podcast: Episode 157: The Geologic Time Scale, 17 Jan 2026 https://podcasts.apple.com/gb/podcast/the-science-of-everything-podcast/id385427377?i=1000745514671&r=588 This material may be protected by copyright.