Fossil Climate

Ichthyologist Carl Hubbs, of the Scripps Institution of Oceanography, has been writing the history of California's climate as far back as 2000 B.C. Five years ago, studying water temperatures off Lower California, he camped at Santo Tomas, and with a true scientist's curiosity about things that did not directly concern him, he dug into an ancient Indian camp site and turned up the shell of a cryptochiton, a large, limpet-like mollusk.

Only a marine biologist would have found the shell exciting. Hubbs knew that cryptochitons do not live, at present, south of Santa Barbara, 300 miles to the north. He deduced that the water off Lower California (and presumably the climate) must have been considerably colder when the prehistoric Indians ate that cryptochiton.

Since then, Hubbs has rummaged through many ancient heaps of kitchen midden and found many shells of creatures that do not live there any more. Some of them he sent to the University of Chicago to be analyzed in two ways: for carbon 14 to tell their age, and for oxygen 18 to tell the temperature of the water in which they were formed.*

The tests showed that since 2000 B.C. the average temperature of the water off Lower California has fluctuated several times by as much as 5DEG. This does not sound impressive, but the difference is enough to count for sharp changes of climate. Dr. Hubbs believes that 300 years ago the weather was more tropical along the Lower California coast. From 700 to 1,100 years ago, it was colder than now. Twenty-five hundred years ago and 4,000 years ago, it was unusually warm. Today that part of Lower California is about as dry as possible; Dr. Hubbs thinks that the region probably got more rain during both its warm and its cold spells. Thus the land may well have been able to support the large Indian population reported, to be living there by the Spaniards during the warm period 300 years ago.

The Hubbs climatic history is still full of blanks, but Dr. Hubbs hopes to fill them in by finding shells from more Indian rubbish heaps. Since charcoal found on the Scripps campus dates as 22,500 years old, primitive man may have been around at least as long as that. If he liked seafood and tossed the shells by his fire. Dr. Hubbs may find them and tell climate-conscious California what kind of climate California had in 20,000 B.C.

*Oxygen 18, a rare, nonradioactive isotope of oxygen, is less abundant in the calcium carbonate of shells formed in warm water than it is in those formed in cold water.

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