#existential risk

https://aeon.co/essays/will-humans-be-around-in-a-billion-years-or-a-trillion

There are good reasons for any species to think darkly of its own extinction. Ninety-nine per cent of the species that have lived on Earth have gone extinct, including more than five tool-using hominids.

No one is certain what caused the five mass extinctions that glare out at us from the rocky layers atop the Cambrian. But we do have an inkling about a few of them.

There are good reasons for any species to think darkly of its own extinction. Ninety-nine per cent of the species that have lived on Earth have gone extinct, including more than five tool-using hominids. A quick glance at the fossil record could frighten you into thinking that Earth is growing more dangerous with time. If you carve the planet’s history into nine ages, each spanning five hundred million years, only in the ninth do you find mass extinctions, events that kill off more than two thirds of all species. But this is deceptive. Earth has always had her hazards; it’s just that for us to see them, she had to fill her fossil beds with variety, so that we could detect discontinuities across time. The tree of life had to fill out before it could be pruned.

Simple, single-celled life appeared early in Earth’s history. A few hundred million whirls around the newborn Sun were all it took to cool our planet and give it oceans, liquid laboratories that run trillions of chemical experiments per second. Somewhere in those primordial seas, energy flashed through a chemical cocktail, transforming it into a replicator, a combination of molecules that could send versions of itself into the future.

For a long time, the descendants of that replicator stayed single-celled. They also stayed busy, preparing the planet for the emergence of land animals, by filling its atmosphere with breathable oxygen, and sheathing it in the ozone layer that protects us from ultraviolet light. Multicellular life didn’t begin to thrive until 600 million years ago, but thrive it did. In the space of two hundred million years, life leapt onto land, greened the continents, and lit the fuse on the Cambrian explosion, a spike in biological creativity that is without peer in the geological record. The Cambrian explosion spawned most of the broad categories of complex animal life. It formed phyla so quickly, in such tight strata of rock, that Charles Darwin worried its existence disproved the theory of natural selection.

No one is certain what caused the five mass extinctions that glare out at us from the rocky layers atop the Cambrian. But we do have an inkling about a few of them. The most recent was likely borne of a cosmic impact, a thudding arrival from space, whose aftermath rained exterminating fire on the dinosaurs. The ecological niche for mammals swelled in the wake of this catastrophe, and so did mammal brains. A subset of those brains eventually learned to shape rocks into tools, and sounds into symbols, which they used to pass thoughts between one another. Armed with this extraordinary suite of behaviours, they quickly conquered Earth, coating its continents in cities whose glow can be seen from space. It’s a sad story from the dinosaurs’ perspective, but there is symmetry to it, for they too rose to power on the back of a mass extinction. One hundred and fifty million years before the asteroid struck, a supervolcanic surge killed off the large crurotarsans, a group that outcompeted the dinosaurs for aeons. Mass extinctions serve as guillotines and kingmakers both.

The only way nuclear war will wipe out humanity is by triggering nuclear winter, a crop-killing climate shift that occurs when smoldering cities send Sun-blocking soot into the stratosphere. But it’s not clear that nuke-levelled cities would burn long or strong enough to lift soot that high.

Tsiolkovsky believed it was human destiny to expand out into the cosmos. In the early 1930s, he wrote a series of philosophical tracts that launched Cosmism, a new school of Russian thought. He was famous for saying that ‘Earth is the cradle of humanity, but one cannot stay in the cradle forever.’

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