Research Journey Toward the Center Of the Earth
MARINE geologist Andrew Fisher says he is excited by a project that's literally ``boring.'' Together with colleagues from 10 nations, he's been drilling into our planet's crust some three miles beneath the sea east of Barbados.
That would seem far removed from normal human affairs. But back at his base at Indiana University in Bloomington, Dr. Fisher explains that this research represents a new phase in studying the internal forces that shape Earth's surface. Instead of just deciphering what's happened in the past, his team and others are studying the crust-sculpting processes as they act today.
These are processes that cause volcanoes and earthquakes. They also influence human history in subtle ways. In the Middle East, they have shaped a landscape where arable zones occur naturally only along a few river valleys and in a thin coastal zone. Competition for scarce resources has led to interminable conflict. The ability to study these important geophysical processes in action is where the excitement lies for Fisher and his colleagues.
Earth resembles a cracked egg. Its crust is broken into about a dozen plates. Where these jostle or move apart, volcanoes erupt, earthquakes rumble, rift valleys open, and mountains rise. Where one plate moves beneath another, such action can be vigorous. Yet the North American plate slips under the Caribbean plate with scarcely a rumble. A layer of highly pressurized water may lubricate their motion. This is what Fisher and his colleagues are probing as part of the international Ocean Drilling Program.
They have drilled into that water layer between the two plates. He explains that ``for the first time we were able to measure'' the pressure there. It is consistent with a water layer that supports the upper plate and lubricates plate motion. The team left instruments in two of their bore holes. Fisher plans to return by submarine and read out the instruments' records next year.
The findings may shed light on a general puzzle. Fisher points out that similar plate movements in the Pacific Northwest have produced quakes. Perhaps his group has found a mechanism that allows movement without buildup of quake-generating strains.
Meanwhile, other research teams in the Ocean Drilling Program plan to drill in the eastern Mediterranean next summer. In this region, the African and Eurasian plates are converging. They hold the region - where so much human history has occurred - in an inexorably tightening vise. This gives rise to the area's legendary volcanic and earthquake activity and shapes its land.
Deep-seated forces drive the incessant plate action. Heat from the planet's core and from decay of radioactive substances provides the energy. They set up convection in the layer between the core and outer crust known as the mantle. Upflows of buoyant material rise while downflows of colder denser material sink, like the currents in a pot of simmering water.
Geophysicists think that these deep-seated convection currents drive the plate action at the surface. They also help keep Earth livable. There's concern that excess carbon dioxide (CO2) from burning fossil fuels may bring an undesirable climatic warming. However, the atmosphere's natural CO2 content keeps the surface warm enough for organic life. Biological and chemical processes remove much of this beneficial heat-trapping gas. Much of the carbon is converted to carbonate sea-floor rocks. These reenter the mantle when carried down by descending crustal plates. There, the carbon is recycled and some of it is sent back into the atmosphere through volcanoes.
Geophysicists are a long way from probing the deep-seated mantle processes. But they are making a beginning with the new study of plate movement processes nearer the surface, such as the quake-free movement Fisher is probing. ``This is a process that doesn't control plate tectonics per se, but it affects how plate tectonics affects people,'' he says.