Trees once caused a mass extinction. Insects grew to the size of dogs.

And 180 million years of reptile rule ended in a single afternoon.

This is the story of everything that has happened since the Cambrian Explosion, when the first animals came into being. Five hundred million years of competition, catastrophe and resurgence, ending with us.
It is also a story of how interconnected our planet is. Life, tectonics, atmospheric chemistry and climate do not have separate histories, but one. They are each part of a single, immutably interdependent system. Life affects the atmosphere, the atmosphere changes the climate, the climate dictates what can live, and the shifting continents act on all three. This coupling is what drives the slow transformations in this story: the rise of oxygen, the drawdown of carbon dioxide, the long cooling into the ice ages. It is also why a single event, such as an eruption or an asteroid, does not stay a single event, but cascades outward through the system, wiping out entire biological lineages.

When the first forests appeared in the Devonian, thirty-metre trees drove roots into bare rock, shattered it, accelerated the weathering that strips carbon dioxide from the air, and pushed oxygen past 90 percent of modern levels. That invasion may also have helped trigger the extinction that ended the period, though not through the air. Phosphorus weathered out of the new soils washed into the seas and fed vast algal blooms, whose decay stripped the water of dissolved oxygen, suffocating marine life. Trees on land, suffocation in the oceans.

In the Carboniferous period, swamp forests buried carbon faster than anything could rot it, producing the coal we are still burning. These forests drove atmospheric oxygen to perhaps 35 percent, almost twice modern levels. Insects breathe by passive diffusion, so their maximum size is set by that number and nothing else. The result was dragonflies with 75-centimetre wingspans and millipedes two and a half metres long.

In Siberia, 252 million years ago, a plume of hot rock reached the surface, causing a million years of eruptions across two million square kilometres. Carbon dioxide surged, the oceans warmed, lost their oxygen and turned acidic, and the ozone layer may have failed. The Great Dying killed roughly 96 percent of marine species and 70 percent of land vertebrates. Forests did not return for ten million years. It is the closest life has ever come to ending.

Both the first dinosaurs and the first mammals emerged from that wreckage. Another extinction cleared the dinosaurs' competition and handed them 135 million years of dominance: 70-tonne sauropods, and one lineage of small feathered predators that descended to birds. Then a ten-kilometre asteroid arrived at 70,000 kilometres per hour, ending the Mesozoic in an afternoon.

The animals that inherited the planet were small, and one of their lineages would eventually produce us. Rising mountains and reorganising oceans cooled the world into an icehouse, and the ice advanced and retreated on an orbital clock. In that oscillating world, roughly seven million years ago, our lineage split from the one that produced chimpanzees.

To put all of this into context, all of recorded human history — every civilisation, every war, every word ever written — occupies roughly one part in a million of the Earth's history.

Chapters:
0:00 Introduction
1:09 After the Cambrian
5:34 The first mass extinction
7:42 Plants and jaws
9:33 The Devonian
11:18 The first forests
13:12 Coal and giant insects
17:28 Pangaea and the Permian
19:25 The Great Dying
21:43 The age of dinosaurs
29:23 Asteroid
31:00 The age of mammals
34:32 Ice ages and us
35:17 Conclusion

#evolution #massextinction #dinosaurs #greatdying #palaeontology #geology #deeptime #science #earthhistory

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