Review: A Brief History of Earth - 4 Billion Years in Eight Chapters

 A Brief History of Earth is a book about earth science/geology. I discovered while auditing a series of Great Courses lectures that I loved the topic and decided to see what a book could give me. I wasn't disappointed, because I discovered that Andrew Knoll in particular articulated the carbon cycle and its relationship to Earth's ice ages in great detail that was enjoyable.

One attractive hypothesis for Snowball onset points to a massive outpouring of volcanic rocks across low-latitude continents. Volcanic rocks consume a great deal of CO2 as they weather, and the warm temperatures found near the equator would ensure rapid weathering and erosion. Thus, tectonic events may have reduced the greenhouse gas carbon dioxide to low levels, cooling the planet and so initiating glaciation. In 1969, the Russian climatologist Mikhail Budyko postulated that as ice spreads from the poles toward the equator, it will reflect more of the sun’s incoming radiation back into space, cooling the planet and, hence, facilitating further expansion of ice sheets (and still more reflection of sunlight back into space). In time, runaway glaciation should envelop the Earth...Evidence from the rocks shows that after millions of years, the ice disappeared quickly, as glaciers retreated to the poles and mountaintops, and then disappeared. What precipitated the collapse of these great ice sheets? Once again, we turn to the carbon cycle. As ice spread across the planet, processes that remove carbon dioxide from the atmosphere—mainly continental weathering and photosynthesis—slowed to a trickle, but processes that add CO2 to air—mostly volcanism—continued apace. Carbon dioxide in the atmosphere built up through time, eventually reaching the critical level at which greenhouse warming set off catastrophic melting. Out with the ice age, in with the Ediacaran Period. (pg. 121-122)

There's great detail about the interaction between flora, fauna, and earth's climates, as well as the catastrophic events that spur massive extinctions, from meteorite impacts to (surprising and new to me, at least), super-volcano eruptions that spew carbon dioxide and lava.

 Spurred by focused heat from the mantle, large volumes of lava have erupted across the landscape or seafloor eleven times in the past 300 million years, providing a mechanism to explain at least one other mass extinction and several smaller events. In the wake of end-Permian extinction, marine life diversified again during the Triassic Period (252–201 million years ago), giving rise to new and distinct ecosystems over an interval of several million years. But the Triassic Period ended as it began, as massive amounts of lava erupted along an arc that extends from Fingal’s Cave off the west coast of Scotland and the Palisades of New York to black cliffs in Morocco’s Atlas Mountains and extensive flows now buried by Amazon rain forest. And again, biological diversity plummeted. The selectivity of end-Triassic extinction and survival in the oceans mirrors that of the Permian, with reefs hit particularly hard. An estimated 40 percent of all genera and up to 70 percent of species disappeared from the oceans, well below the numbers for end-Permian extinction, but still dramatic. (page 187)

 This stuff is dramatic and told well. I have friends who'll point to this stuff as reasons for not worrying about climate change, since earth and earth life has survived so much catastrophe before. But that's cold comfort for humans --- since humanity's existence isn't any more necessary for life on earth (in general) than having an oxygen rich atmosphere!

The author's very careful to note how during human lifetimes, ecosystems such as fisheries are also fragile, and can take a long time to recover:

Cod populations that yielded more than 800,000 tons of catch in 1958 were declared commercially extinct in 1992, altering the very cultural fabric of adjacent Newfoundland. Commercial fishing was banned, but nearly three decades later, the cod have yet to recover. (pg. 215)

The book is short, tells its story well, and provides lots of lessons and interesting pieces of knowledge. Recommended.