Millennia of alternating global warming, punctuated by years of freezing cold, killed off most life on earth. As Siberian volcanoes erupted for thousands of years, the coal deposits also burned, releasing deadly toxic gases, and methane trapped in ice was also released. More to the point, all those buried trees contributed to the “Great Dying” of 250 million years ago, which nearly wiped out life on Earth - we revisit the “Halls of Extinction,” the notional museum to the great mass extinctions of prehistory, that Tyson introduced in the second episode. Sorry, creationists - it didn’t all happen during Noah’s Flood. He shows us a petrified tree, upright in the rock strata, and damned if the first thing I thought of was the young-earth creationist claim that such fossilized trees somehow create a problem for the idea that rock strata formed over millions of years - how can one tree protrude through supposedly eons of layers huh? The answer is a bit more boring - the “fossil forests” may have been covered fairly rapidly, then the trees slowly fossilized later, over longer periods, other layers of sediment built up over time, eventually surrounding an already-fossilized tree. This got messy eventually - twice.īut first, we take a quick jaunt to Nova Scotia’s Joggins Cliffs, where millions of years’ of sediment can be seen as you move along the beach. And so eons of forests were buried, their carbon eventually becoming coal. All those trees ended up getting buried without decaying much, since bacteria and fungi hadn’t yet evolved a means of digesting lignin.
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With all that photosynthesis going on, there was more oxygen than at any time in the planet’s history, arthropods were huge, and virtually all the planet’s land mas was a supercontinent, Pangea.
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Neil deGrasse Tyson starts us off with a visit to the Carboniferous period, roughly 350 million years ago, at the point where trees began to cover the planet, the result of a newfangled plant molecule, Lignin, which allowed trees to grow higher - and so, with nothing getting in their way, they did. This week’s episode of Cosmos: A Spacetime Odyssey, “Lost Worlds of Planet Earth,” is about time travel - the path of all the life that clings to the thin habitable crust of our planet, and the forces that have shaped both.