When Life Nearly Died: The Greatest Mass Extinction of All Time by Michael Benton

This is a book about ancient life and ancient climate. The following is a related note about climate and some quotes from the book.

What cause the climate catastrophe?

Sunlight is the most universal and the most important resource for life. Almost all life depends on sunlight to survive, directly or indirectly. Climate catastrophes are usually caused by the drastic reduction in solar energy received by the earth. This situation often occurs in two ways.

The first is the dramatic increase of dust in the atmosphere, which will block much of solar energy reaching the earth. This can be caused by eruptions of large volcanos, as at the end of Permian period, or by the impact of a huge asteroid, as at the end of the Cretaceous period.

The second is the positive feedback between the decline of temperature and the increase of ice and snow on the earth’s ground. The decline of temperature below the freezing point will generate ice. Ice will reflect much of sunlight, which will further depress temperature. If the temperature of the earth becomes lower than freezing point for large enough area for long enough time, the mechanism of positive feedback makes large part of the earth covered by the ice, which is unfavorable to the growth of most living systems. This occurred at the period of Snowball Earth, when most life were destroyed. During the glacial periods, the amount of life is greatly reduced.

The increase of carbon dioxide, by itself, will not increase the dust in the atmosphere. The increase of carbon dioxide will increase the earth’s temperature, making it harder for the earth to become a snowball. The increase of carbon dioxide is especially helpful in a geological time with mostly glacial periods. Mass extinctions are mostly caused by global cooling (Stanley, 1988)

However, during volcano eruptions, dust and carbon dioxide are often released together. Dust reduces the amount of sunshine reaching the surface of earth, causing death to plants. The reduction of plants causes the reduction of other life along the food chain. The decomposition of dead organisms further increases the amount of carbon dioxide and reduces the amount of oxygen, which makes the environment less hospitable to most life. Mass extinction releases great amount of carbon dioxide, which will increase the temperature. The periods of mass extinctions are often associated with high carbon dioxide concentration in the atmosphere and high temperature. But this may not mean the increase of carbon dioxide and temperature causes mass extinctions. Rather, it could be the mass extinctions cause the increase of carbon dioxide and temperature. Some periods of high temperature, such as the Early Eocene Climatic Optimum and the Holocene Climate Optimum, were not thought as periods of catastrophes. Instead, humanity thrived during the Holocene Climate Optimum. Further research is needed to explore the relation between the climate and life.

There are many unanswered questions of climate catastrophes. One is the timing of the great extinctions of life. Over geological time, there are five great extinctions. The period and time of these great extinctions are

Of the five great extinctions, the first, the third and the fifth have the highest extinction rates. See Figure 18 of Benton (2003) for details. The third extinction, the Permian great extinction ended the Paleozoic era. The fifth extinction, the Cretaceous great extinction ended the Mesozoic era. The time difference between the first to the third is about 188 million year. The time difference between the third to the fifth is about 187 million year. The time differences between the first to the third and the third to the fifth are almost identical. Is this a coincidence? Or is there a connection between these extinctions to some periodic celestial movements?

Imagine some periodic encounters between the solar system (or the earth) and some meteoroid or asteroid ring with a period of about 188 millions. This could explain the occurrences of the first, third and fifth great extinctions. It is generally accepted that the end of Cretaceous extinction was caused by the impacts from a huge asteroid. The evidences of impacts from earlier events could be harder to trace. The relation between the earth’s climate and the celestial movements is still at an early stage of research.

Lyell’s four usages of the word ‘uniformity’ are:

• The uniformity of law: the laws of nature are constant through time; it would be wrong to suggest that the orbits of the planets, gravity, mechanics, the interactions of chemical elements or any other such fundamental laws of nature have changed.

• The uniformity of process: the use of observations of modern phenomena to interpret the past, sometimes termed actualism. Geologists should not invent processes that cannot be seen today to explain ancient rock formations.

• The uniformity of rates: processes in the past must be interpreted to have occurred at the same rates as they do today, sometimes termed gradualism. So, geologists should not posit massive catastrophes, floods, volcanic eruptions or meteorite impacts on a larger scale than can be observed today.

• The uniformity of state: change on the Earth has happened in a cyclical way, and there is no evidence of linear, or directional, change, sometimes termed nonprogressionism. Lyell argued that change does not go anywhere, but that the Earth is in dynamic balance, with climates, volcanic eruptions, deposition of rocks and other phenomena proceeding at fairly constant rates somewhere, all the time. (Chapter 3)

Comments: The last two, especially the last one, meaning of uniformity are very similar to today’s mainstream economic theory.

The first two meanings of ‘uniformity’ are indeed sensible. Of course a true observational scientist should use the current laws of nature, and modern processes, in explaining past phenomena. This is a mixture of the actualistic methodological approach and the uniformitarian philosophy. A geologist clearly could not function by speculating rather than observing, or framing explanations in wild and imaginative theorizing.

But these same messages had also been the solid underpinning of everything Cuvier had written about geology from the start. Indeed, Cuvier’s great initial distrust of geology and geologists stemmed precisely from his contempt for their wild theoretical models of the Earth, based on minimal evidence. This he repeated time and time again,  including in his 1810 and 1812 essays. Cuvier also stressed with great clarity that the geologist must base everything on modern processes and the modern laws of nature. (Chap 3)

Comments: We should take the same attitude in economic theory. Economic theory should be consistent with physical laws.

Lyell employed the most amazing sleight of hand in trying to convince geologists of his notion of uniformity of state, or his grand cycles of history. A consequence of the stately steady-state Earth was, in his view, that nothing ever changes. Volcanoes erupt, glaciers advance, sea levels go up or down, but everything is in equilibrium. He viewed the Earth as a closed system with certain fixed laws, and that meant that there could be no progress or direction of change. And this he extended to life. Lyell could not in any way accept a time of origin for life as a whole, nor a decisive point of extinction for any group. (Chap 3)

The evidence for impacts had been so obvious that it could be denied only by a supreme effort of will. (Chap 5)