Scientists Share Insights About Earth : Other Planets Hold Key to Mystery
New information from the study of other planets is causing scientists to revise many of their theories of the forces that drive the Earth, a team of planetologists said Wednesday.
The insights they are gaining could help explain long-range changes in the Earth’s climate, the dynamic forces that cause mountains to rise and oceans to spread and possibly even the extinction of mammals that once ruled the planet.
Rich storehouses of information collected by planetary probes and new telescopes have turned the solar system into a laboratory in which scientists can compare commonly accepted ideas about the dynamics of the Earth with other planets. What they are finding, quite often, is that many of the old ideas do not hold up.
“Much of the progress has been backward in the sense of getting rid of ideas that don’t fit,” Caltech’s Bruce Murray told scientists attending the national meeting of the American Assn. for the Advancement of Science in Los Angeles.
Scientists are learning, for example, that many of the phenomena that had previously been thought to have been caused by forces solely within the Earth must depend partly on outside influences, because what holds true for the Earth does not always hold true for the other planets. That includes such things as the Earth’s magnetic field, which has not been found around planets where it should have been if earlier theories were on the mark.
Keys Are Far Away
Scientists say that such findings may mean that many of the secrets of Earth can best be unlocked far away.
“The whole concept of the early history of the Earth is being revised,” said Murray, former director of the Jet Propulsion Laboratory and an architect of many of this country’s planetary missions.
In describing the state of planetology today, Michael Carr, an astrogeologist with the U.S. Geological Survey in Menlo Park, said: “The intent is to come up with general laws for the evolution of the planets.”
That, in turn, should lead to fuller understanding of what makes the Earth tick and what can be expected in the future. That could be extremely important in such areas as long-range weather changes.
“Clearly, the climate of the Earth is changing,” Murray said. Major change “on the scale of 100 years becomes a very big deal,” he added, because a gradual reduction in temperature could lead to the inundation of much of the Earth.
For many years it was thought that climatic changes--such as an ice age--were brought about by the Earth’s internal forces, including the release of heat from the molten core and the movement of the continents on crustal slabs, called tectonic plates.
‘A Little Implausible’
“There are some internal possibilities,” Murray said, “but they seem a little implausible.”
If such things as an ice age were brought on by “an external force, that should affect the other planets,” he said.
Mars, he said, has no oceans, but “dust and ice do get transported, indicating cycle changes on Mars.” If solar radiation brought about enough changes to cause an ice age on Earth, “that should be provable by examining Mars,” because similar events should have taken place there and would be reflected in the layering of strata on the surface of the planet, he added.
One of the biggest puzzles is the absence of magnetic fields around planets that should have them.
It has long been thought that the convection of heat to the Earth’s surface from its molten core, coupled with the rotation of the planet, “produces a dynamo” resulting in a magnetic field, Murray said.
Scientists were surprised to learn that Venus, which is similar to the Earth in many ways, does not have a magnetic field and that Mercury, which is quite different, does.
‘Like a Test Bed’
Using the “solar system like a test bed,” Carr of the Geological Survey would like to learn why some of the Earth’s volcanoes behave differently than others. Why, for example, does one like Mt. St. Helens blow its top while other volcanoes in Hawaii simply spread out?
“The most spectacular volcanoes” known to man are on Mars and could offer insights into the behavior of those on Earth, Carr said. That is because, although Mars and the Earth are thought to be about the same age, they are in vastly different stages of evolution. A close look at Mars should tell scientists more about what the Earth was like 2 billion or 3 billion years ago.
Some of the planets, especially those farther from the sun, captured much of their mass in collisions with passing asteroids and comets. That process of accretion is still going on, but at a much slower rate.
Although he did not predict one in the near future, one panelist said a collision between the Earth and a large asteroid would lead to far greater devastation than nuclear war, quite possibly leaving the Earth uninhabitable.
“Asteroid impacts are nothing to mess around with,” said Brian Toon, research scientist with Ames Research Center in Mountain View, Calif.
Dinosaur Extinction
Such a catastrophic event has been blamed for many things, including the extinction of the dinosaurs, but Eugene Shoemaker, an astrogeologist with the Geological Survey, offered a new twist to that much-discussed theory.
Shoemaker said he believes that the extinctions were caused when a giant object crashed into one of the Earth’s oceans, not into one of its continents.
“An impact in the ocean puts a tremendous amount of water into the stratosphere,” Shoemaker said. “Dust will fall rather rapidly, but getting the water out of the upper atmosphere takes much longer. Years, possibly hundreds of years.”
Shoemaker, who indicated that he has no doubt that such an event wiped out the giant mammals, said that after such an impact, “it gets very cold and dark, then very quickly it gets warm, releasing lots of carbon dioxide from the oceans.”
He said he believes that “lots of these critters died” from the rapid change in temperature.
