Doomsday for Earth projected as a billion years away

December 24, 1992|By New York Times News Service

Life on Earth may be doomed, but not for at least a billio years, two scientists suggest.

This new estimate gives Earth's creatures a tenfold increase in life expectancy over a span proposed earlier. The latest estimate, by Dr. Ken Caldeira, a geochemist, and Dr. James F. Kasting, an atmospheric scientist, both of Pennsylvania State University, is based on a complex mathematical representation of interactions in the environment.

For many reasons, scientists believe that life on Earth cannot survive indefinitely. For one thing, the sun, which is a common type of star, is expected to expand into a red giant, the outer

shell of which will eventually engulf the orbit of the planet Mercury and roast the Earth. The Earth would then be burned clean of life in five billion years.

But many scientists believe that by that time life will have long since disappeared for other reasons.

The mathematical model developed by Dr. Caldeira and Dr. Kasting, which was described in an article being published today in the British journal Nature, supports earlier predictions that the Earth may meet its doom through a precipitous decline )) in atmospheric carbon dioxide. That would starve plants and destroy the planet's food chain.

The idea, proposed a decade ago by a British environmental scientist, Dr. James E. Lovelock, and his colleague, Dr. M. Whitfield, is based on the belief that as the sun becomes more luminous, the Earth will gradually heat up. Solar heating will enable the Earth's silicate rocks to react much more readily with atmospheric carbon dioxide, thereby removing it from the air.

Although this process would slow the greenhouse warming of the Earth, it would also rob plants of the raw material they use to photosynthesize carbohydrates.

Dr. Lovelock predicted that within 100 million years the Earth would run out of food.

In the next phase, solar heating would eventually prevail, vaporizing the planet's water, splitting water molecules into oxygen and hydrogen and hurling the hydrogen into space.

Where Dr. Caldeira and Dr. Kasting part company with Dr. Lovelock is in their estimate of the rate of change in the decline of the greenhouse effect. In their model, the Penn State scientists calculate that despite the increasing heat of the sun, the temperature of the atmosphere is likely to remain fairly constant for 900 million years because the warmed rocks will take carbon dioxide from the air and reduce the greenhouse effect.

Of course, Dr. Kasting says, various unpredictable catastrophes could snuff out life much sooner.

"You never know what might happen," he says. "But with any luck, and with a billion years to play with, the human race would seem to have plenty of time to solve its problems."

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