Skirting the edge of destruction

 kw: book reviews, nonfiction, natural disasters, apocalyptic imagery, history, quests

Craig Childs is an adventurer. A couple of decades ago he became enamored of the idea of exploring those portions of Earth that epitomize various ways natural events could do away with civilization, even humanity, and perhaps all life. He wrote about these experiences, and waxed lyrical about them, in his 2012 book Apocalyptic Planet: Field Guide to the Everending Earth. The picture here is in no way a likeness, but an evocative generated image.

I see him imagining the planet musing, "How might I kill you? Let me count the ways." He chose nine ideas to instigate nine adventures, such as crossing a couple of deserts (the Sonora and a salar in the Atacama), spending a couple of weeks "helping" scientists gather data in the middle of the Greenland ice cap (I suspect he'd have preferred Antarctica, but getting sponsored to go there is infinitely harder), running a river of Class VI rapids in the Himalayas (all by itself that exposes you to a dozen ways to die), or spending just a couple of days crossing an Iowa cornfield to see if anything except corn can live there (spoiler: no surprise, it's darn little, a list that can fit on the back of a business card, mostly bugs and tiny plants). I can do no better than to list the chapter titles, with my instant summaries in brackets:

1. Deserts Consume [Sonora Desert, Mexico]
2. Ice Collapses [Glacier in Patagonia, Chile]
3. Seas Rise [St. Lawrence Island in Bering Sea off Alaska]
4. Civilizations Fall [Squaw Peak/Piestewa Peak near Phoenix, AZ; side journey to Maya country]
5. Cold Returns [Greenland, far uphill from the west coast]
6. Species Vanish [Iowa cornfield; a few square miles of monoculture]
7. Mountains Move [Salween River, Tibet]
8. Cataclysm Strikes [Lava field in Mauna Kea, HI]
9. Seas Boil [Atacama Desert, Chile]

The basic message, reiterated often, is that this is a favored time to be on Earth. Bad times of numerous varieties come and go, but each chapter illustrates for us ways the Earth can outdo anything encountered in human history. Greatly outdo. For example, if you are old enough to remember the Mt. St. Helens eruption of 1980, you might recall the thick dust we all had to wash off everything, all over the U.S. (and a number of other countries). All that was from the expulsion of about one cubic km of material, which blasted ahead of it another 2-3 cubic km of existing rock and ash. Eleven years later Mt. Pinatubo ejected 10 cubic km. In 1912 the largest eruption of the 20th Century, Novarupta, was a further three times as large.

Volcanic eruptions are scaled, similarly to earthquakes, by a scale called VEI, Volcanic Eruption Index. Each number on the scale is a factor of 10 larger than the one before. Mt. St. Helens was VEI 5 and the other two mentioned were VEI 6.0 and VEI 6.5. The scale goes as high as almost 9, and an eruption of VEI 8.0 releases 1,000 cubic km. The most recent VEI 8 eruption was the Taupō volcano in New Zealand, 27,000 years ago. The largest known eruption in geologic history was one of eight VEI 8 or larger eruptions that occurred in Paraná Province, Brazil about 132 million years ago, a VEI 8.9, with an eruptive volume of 8,600 cubic km. All of those eight eruptions were larger than the largest eruption from the Yellowstone caldera, the "supervolcano" of recent hype. See this list for more information.

That's all just one kind of event that makes a serious dent in the global ecosystem. The message of the book is that Earth has a lot of ways to make our life miserable at the very least, and perhaps to terminate it. So far, our comparative good fortune has held.

The lyrical writing makes the book enjoyable to read. I was rather astounded at the amount of misery suffered by the author and his companions (he never adventured alone). "Better he than me!" The more optimistic message I see is that life has persisted on Earth for very nearly four billion years, in spite of VEI 8 volcanoes, iceball stages that left no liquid water on the surface, even at the equator, and titanic flooding events; all this in the face of a warming Sun, which is 30% hotter now than four billion years ago, and will be 40% hotter than it is now in another 5 billion years, just before it becomes a red giant and heats up by another factor of about 100. At that point, the sky will be nearly half filled by searing orange light emitted by a thin gas with a temperature of at least 3,500°C (6,300°F). The planet itself will melt. In the meantime, we have perhaps a billion years to figure out how to migrate to the stars. Cheers!

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Errata: I must deal with two egregious errors.

Firstly, in page 90 we find, "…a quarter of the earth is covered with water." Hardly!! The ocean covers 70.8% of the planet, almost three-quarters. If we consider fresh water in all its forms, lakes and rivers add less than 1%, while ice caps (Antarctica and Greenland) make up another 2.8%, leaving something over 74% of earth covered by ocean, ice, or fresh water.

Secondly, and much more serious: On page 290 the author writes that the impacts of gigantic planetesimals during the Late Heavy Bombardment as it is called, prior to 3.8 billion years ago (and beginning 4.2 billion years ago), triggered nuclear reactions that produced major radioactive isotopes, particularly the long-lived isotopes of thorium, uranium and potassium. The amount of heating needed to produce nuclear reactions is not in the thousands of degrees (during the LHB the core may have exceeded 15,000°F or 8,300°C) but in the millions or tens of millions of degrees. LHB heating cannot have had the slightest effect on the isotopic abundance of the Earth, although various isotopes would have been included in the impacting bodies already. However, there is an interesting side point here, which the author also misses. Let's look back at the three isotopes mentioned, going back 4 billion years, which we will call T0:

• Th-232, half-life (T½) 14.2 billion years (Gy). Four billion is only 28% of a half-life, so going backwards, we find that at T0 there was about 20% more Th-232 than there is today.
• U-238, T½ = 4.5 Gy. At T0 there was almost twice as much U-238 as today.
• U-235, T½ = 0.70 Gy. Four billion is 5.7 half lives, so at T0 there was 40 times as much U-235 as today. At present, U-238 is 138 times as abundant as U-235, but at T0 the ratio was about 7:1.
• K-40, T½ = 1.26 Gy. Four billion is just over three half-lives, so at T0 there was about nine times as much K-40 as today.

If these figures are put together with present abundances of each isotope (a few parts per million), it balances out that radiogenic heating, just from these four, was about six times as much as it is today. There may have been other isotopes present when Earth was formed, but because the universe was already about nine billion years old, anything short-lived that hadn't been very recently forged in nearby supernovae would have been long gone.

More radiogenic heating most likely led to early initiation and more rapid plate tectonics once the LJB-induced melting subsided and the crust formed. The Earth as a whole could have been warmer and stayed so for a good while as a result, offsetting the reduced heating of the 30%-cooler Sun. We know so little of that era, but it is clear that life started as soon as liquid water was able to remain and accumulate. Life is an active agent, and has "conspired" for almost 4 billion years to keep Earth habitable.