This book makes me feel very small.
The key takeaway of The Life and Death of Planet Earth: How Science Can Predict the Ultimate Fate Our World (Times Books, 2003), Peter Ward and Donald Brownlee’s follow-up to their earlier book, Rare Earth (Springer, 2000), is that complex life has been — and will be — on this planet for only a short period of time: a billion years out of the planet’s 12-billion-year estimated lifespan, and we’re already past the halfway point. The end of multicellular life is only a few hundred million years away, when so much carbon dioxide is sequestered away that plants suffocate. Of course, at that point the increasing output of the sun will render the planet too hot to inhabit in any event: the future, they argue, strongly resembles Earth’s Archean past, where the temperatures are hot, the atmosphere is toxic, and nothing more complex than bacteria can survive.
This is a really big-picture look at our planet, one that makes our presence upon it look very tenuous indeed. Everything on our planet is in flux, not static, every change we make to our world insignificant in terms of the big picture. The Earth of a few hundred million years ago was warmer, more biodiverse and had more CO2 in the air; our “normal” is the result of hundreds of million years of carbon sequestration by plants that has led to cooler temperatures, low CO2 levels — and ice ages. We are creatures of the interglacial period. Indeed, they point out while global warming is a problem in the immediate near term (and by immediate I mean the next few centuries), the glaciers are coming back; global warming may delay them, but the carbon cycle is inexorable.
In astrobiological terms — the search for life on other planets — the authors point out that the Drake equation needs another variable: the “habitable life span” of planet, the time during which a planet can sustain multicellular life. In Earth’s case, that’s one-twelfth of its existence.
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