Third International Palaeonological Congress I'm currently attending in London, which notwithstanding inasmuch as which is reputed to be the biggest meeting of palaeontologists in the world, ever - the noosphere round South Kensingtion is in imminent danger of going critical and disappearing in a welter of brachiopods. Being as it's so huge, with many parallel sessions, I have managed to attend only a fraction of the events, gatherings, panels, discussions and symposia.
It is a truism, perhaps, to say that you can't have a fossil unless you can have a rock to put it in, so one symposium I was keen not to miss was the Lyell Symposium, whose subject was working out how best to appreciate the tally of past diversity, given that the record of the rocks itself is not constant. Sedimentary rocks are forming all the time, but they are constantly being worn away. Rocks that were once formed on the ocean floor are thrust up as mountains which, by virtue of their high estate, experience greater weathering. But even those rocks that lie peacefully on the seafloor will, eventually, be subducted beneath continental margins. As we say at the Maison Des Girrafes, dynasties will rise and fall, mountains will be thrust from the ocean floor and ground away to dust, and even continents will be seen to drift measurably apart, all in the time we're waiting for Crox Minor to tie her shoelaces. No strangers are we to the grand cycles of Earth History.
Interpreting, therefore, the known ranges of fossil organisms is fraught with complexity, if what you are doing is using those data to make bald statements about the history of life. The baseline for such grand macroevolutionary vistas was and is the database on marine invertebrates compiled by the late Jack Sepkoski and now maintained by Shanan Peters of the University of Wisconsin, Madison. Peters was among the first to realize that the record of the rocks might have a substantial modulating effect on apparent signals of changing diversity. In other words, many of the events that raw biodiversity data seemed to describe would be blurred or even disappear entirely once that biodiversity had been corrected for the availability of rocks in which fossils might be preserved. Many of the supposed crises in Earth history - the mass extinctions, the originations - were in fact artefacts caused by the fact that the record of the rocks themselves, as well as the fossils they contained, is inconstant.
Things have moved on a little since then, and Peters and many others have been looking at the possibility that some of these factors are in fact connected. Is there a relationship between the amount of sedimentary rock deposited and the activities of life? Perhaps the abundance of life is not just correlated with available sediment, but has a causal relationship. In one sense this must be true. The chalk that makes up the famous White Cliffs of Dover, for example, is almost entirely biogenic. And when you start to plug in the effects of life into the Earth System, you see connections everywhere. The presence of life substantially affects the hydrological cycle, the rate at which rocks are weathered, the constitution of the atmosphere - and, one even make so bold - the wetness of rocks in subduction zones and thus the course of plate tectonics. Life, the fluid earth, and the solid earth, are all connected. From this it seems obvious that the record of life on earth cannot be read independently from the record of the rocks themselves. But teasing apart causes from effects is a project that imposes new challenges, creating exciting new statistical methodologies, and showing the history of the Earth and the life upon it are intimately, indissolubly linked.
You might think palaeontology is just a lot of old bones and shells.
We, however, know that fossils are the signs of a planet shaped by that remarkable nonequilibrium phenomenon we call 'life'.
2 months ago