The Great Extinction: The Solution to One of the Greatest Mysteries of Science by James Lovelock

Author:James Lovelock [Lovelock, James]
Language: eng
Format: epub
ISBN: 9780385180115
Google: QpjuAAAAMAAJ
Amazon: 038518011X
Published: 2022-07-27T22:46:52+00:00

THE CREAT EXTINCTION

focus of the event. They would recover quite soon. Their mysterious, anonymous lives would continue, which means that evolution itself could continue.

Evolution did a great deal better than merely continue, and if we are to understand what happened next, we must try to discover not what it was that killed so many species-we think we know thatbut just how it killed them. From what cause did the species die?

What shall we write on their death certificates?

7

Causes of Death

We have made much of the curious chemistry of the boundary clays that mark the end of the Cretaceous. It is time now to say a little more on the subject, for it is not only their content of metals that distinguishes them from the strata above and below them.

In the last few years a new technique has been developed that is used in the reconstmction of past climates. There are two important isotopes of oxygen ( 16 and 18) that exist in the Earth’s atmosphere. On average, 99.76 percent of atmospheric oxygen is oxygen 16 and about 0.2 percent is oxygen 18. The proportion of one isotope to the other was determined by the original supernova that produced the elements from which the solar system is composed. It is fixed, therefore, and remains constant. \Vhen carbon is oxidized to form carbon dioxide, the proportions of the oxygen isotopes is preserved, the carbon dioxide containing them in the same proportions as they are found in atmospheric ( or any other) oxygen.

Carbon dioxide is the gaseous form of a very weak acid, carbonic acid. Small amounts of carbon dioxide dissolve in water, where they react with metals to form carbonates of those metals. Some metallic carbonates, most notably calcium carbonate, are taken up by living organisms, which use them in the construction of their own bodies. The organisms most dependent on calcium carbonate are the mollusks-the snails and shellfish-and the countless microscopic species that dwell among the plankton, the mass of organisms ranging in size from single cells to the larvae and fry of many fishes which drifts near the surface of the sea and in large bodies of fresh water. However, these organisms select one oxygen isotope in preference to others, so that a biological selection mechanism exists. When the organisms die, their calcium carbonate remains,

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THE GREAT EXTINCTION

which are insoluble in water, are often preserved and they retain the selected proportions of oxygen isotopes.

The release of carbon dioxide into the atmosphere, the formation of carbonates, and the size of populations of organisms which use calcium carbonate all depend on climatic conditions, most especially on temperature. Sedimentary rocks that have been subjected to much deformation and compression over millions of years may provide little direct detailed evidence of the amount of biological activity occurring at the time they formed, but they are likely to contain the remains of organisms in the form of calcium carbonate.

Consequently, an analysis of samples from those rocks that determines the proportions of the isotopes of oxygen will

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