When Life Nearly Died: a Book Review
By Heather Campbell
Atheists generally think of themselves as skeptics, but on the topic of evolution, religionists think we're the gullible believers. Our experience with evolution could be applied to another pressing scientific issue, global climate change. As with evolution, there is quite a consensus among the scientific community (in this case, that climate change is human-induced and very real); the disagreement is over details of how and how much. Also, very similar to evolution, this basic consensus is misleadingly portrayed in the media as more of an even split, with naysayers given fairly equal time despite being in the minority.
One book I recently read, "When Life Nearly Died" (Michael J Benton, Thames and Hudson, 2003), addresses both evolution and climate change. The stated topic is the most destructive extinction event in Earth's prehistory, the one that occurred at the boundary between the Permian and Triassic periods (about 251 million years ago). This event wiped out 70-90% of marine and terrestrial species, apparently relatively suddenly. The more famous extinction 65 million years ago which saw the end of the dinosaurs was actually much less profound. According to Benton, evidence suggests that a runaway greenhouse effect was a factor in the P-T extinction.
About two thirds of "When Life Nearly Died" is devoted to an account of the scientific discovery of Earth's prehistory. That is, we start out by learning how geologists of the early 1800s came to believe that Earth was much older than previously thought, and that much flora and fauna had once thrived but somehow disappeared. This part of the book has won praise from lay readers as being a very engaging historical outline. Benton introduces a cast of characters -- some quite colorful, considering that they are geologists -- and in the process, underscores the fact that ideas of evolution and "deep time" are not just Charles Darwin's but rather were worked out by many minds as they analyzed the evidence. The case is built, brick by brick, on a firm foundation of facts.
Only the last third of the book or less deals directly with the reconstruction of the Permian-Triassic extinction. Here the line of reasoning becomes more technical, and the implications are most chilling.
Benton believes that the P-T extinction was initiated by prolonged lava flows from volcanic fields in Siberia. Such eruptions could have spewed enough sulfur dioxide to stress the vegetation, and enough carbon dioxide to raise the planetary temperature 2-3 degrees C. He presents geologic evidence for his case, and argues against the alternative theory -- that a meteorite impact caused these conditions. (I have heard a stronger case made in favor of impact from other sources, however).
The problem for scientists was that neither of these initiators would have been enough to cause the massive anoxia (lack of oxygen) seen in marine deposits in the form of black shales. Such sedimentation indicates that vegetation was no longer taking up carbon, and even dead vegetation was not being decomposed as normal; the productivity of the biosphere had profoundly collapsed.
The answer to this mystery came in the form of deposits of "gas hydrates" of methane. These deposits of methane molecules trapped in a cage of water molecules were discovered in ocean floors in the 1970s. They form in conditions of great pressure and (most often) low temperatures. Methane is 20 times as effective as CO2 at trapping infrared radiation in the atmosphere, so a major release could cause remarkable temperature increases. The carbon in methane tends to be isotopically light, and in fact the geologic record of the time shows a shift in the carbon isotope ratio towards light carbon.
The most plausible scenario, according to Benton, is a 2-3 degree temperature rise causing destabilization of gas hydrates, which pushed the temperature increase up to about 6 degrees greater than average, fairly rapidly.
What Benton does not explicitly refer to is the fact that this kind of temperature increase is at the upper end of the range predicted by the International Panel on Climate Change (IPCC). The IPCC's models apparently do not take into account possible compounding effects of gas hydrates, the deposits of which are estimated to weigh in at 10,000 gigatons.
Some basic facts of climate are not too difficult to grasp. The average temperature over the surface of the earth is 60 degrees Fahrenheit (17 or so C). If there were no greenhouse gases (such as water vapor and CO2) in our atmosphere, however, the average temperature would be about 0 degrees F. This profound effect on our temperature occurs even though greenhouse gases are present at very low concentrations - carbon dioxide is measured at 370 parts per million now. Ice core samples from land-formed glaciers show that the pre-industrial level of CO2 was 280 parts per million (air is trapped in the snow which accumulates into the glacier). A thirty percent increase in the gas which accounts for about one quarter of the greenhouse effect can be expected to push the temperature upwards.
In fact, the average temperature has increased by about half a degree C over the past century, which may not sound like much but is already changing ecosystems in the Arctic. The thickness of the ice cap at the North Pole has decreased about 30%, according to submarine readings. Over the last 100 years, global sea level has increased 4 to 14 centimeters.
In June, the CEO of Shell Oil in England, Ron Oxburgh -- who has a PhD from Princeton in the geosciences -- told the Guardian that if we don't start sequestering carbon now, he sees "very little hope for the world".
If change occurs gradually, humanity can probably adapt. However, ice core samples have shown that climate change can occur rapidly, in the space of a few decades in some cases. With gas hydrates lurking in the ocean floors, there is a possibility that we are risking extreme change in a relatively short time period. This possibility may be small, but the prospects are horrible, to say the least. Just as we wear seat belts even though the chance of an accident on any particular day is remote, we should take protective action on this issue now. Atheists and others who try to have science as a basis for our choices could contribute greatly to motivating the public.
- Wolfson, Richard. Energy and Climate: Science for Citizens of Global Warming, The Teaching Company, 1997.
- Maslin, Mark. "The Coming Storm", Barron's, 2002.