Tuesday, August 30, 2005
Could lava tell history and predict the future?
They think their research can help explain what is happening to our warming world.
The extent of some of these buried lava flows is mind-boggling. Fragments left by a series of eruptions 200 million years ago in what now is the Atlantic Ocean stretch across four continents, from New England to France and from the Amazon to West Africa.
An even larger outburst, 120 million years ago off the Indonesian island of Java in the southwest Pacific, slathered molten rock over more than 1.2 million square miles of ocean floor, enough to cover Alaska or Western Europe with a layer up to 18 miles thick.
Along with somewhat smaller — but still enormous — volcanic eruptions on land, these belches from the planet’s fiery interior contributed to a series of mass extinctions of most of the organisms that were alive at the time.
Although the extinctions were devastating to life, scientists think they opened the way for new, more advanced creatures to evolve, including humans.
Mass extinctions have “radically changed the types of life on Earth, because rapid evolution after each disaster led to the older forms becoming replaced by newer forms,” said Gregory McHone, a geologist at Wesleyan University in Middletown, Conn.
The blasts from the past may have ominous implications for future climate change, some scientists say.
“The rapid release of carbon dioxide into the atmosphere, happening today, appears to have happened in the past, too,” said Paul Wignall, an earth scientist at the University of Leeds in England.
“In many ways, these rapid and giant eruptions seem to replicate the effects of fossil-fuel burning, and so have provided natural experiments closely similar to human activity,” Wignall wrote in an e-mail. “The consequence of rapid warming of oceans and atmospheres appears to be mass extinction.”
Lava is a common type of rock that has been melted by temperatures as high as 2,000 degrees Fahrenheit and flows from a volcano or cracks in Earth’s surface. It rises from a 400-mile-thick layer of hot, gooey material, known as magma, that lies between the planet’s crust and its solid core.
The vast expanses of seafloor lava — technically known as “large igneous provinces” — are “one of Earth’s most fascinating features,” said John Mahoney, a geologist at the University of Hawaii in Honolulu. “They provide insights into the causes of major environmental and biological changes in the past,” he wrote in an e-mail, and “almost certainly played an important role in bringing about these extinctions.”
Most of the oceanic lava sheets are invisible from the surface, but Earth’s continents also bear traces of huge volcanic eruptions, some of them recent.
Yellowstone National Park in Wyoming, for instance, contains a 50- by 40-mile crater left by a series of eruptions, averaging about 600,000 years apart. The last explosion came 630,000 years ago, so the park is overdue for another.
“Eventually, Yellowstone will erupt again,” said Don Hyndman, a geologist at the University of Montana. “When it does, I don’t want to be living in Bozeman” — 90 miles away. “The last event blew ash as far as Kansas and Arkansas.”
It produced enough lava, ash and rock to cover New York state 67 feet deep, he said.
Although geologists have known for decades about the lava provinces, many questions remain about these extraordinary structures. More continue to be found. A new one was reported in July under a large area of western Australia.
Exploration of the lava beds also is turning up new sources of valuable minerals, said Don Schissel, an executive with BHP Billiton, a global mining company with headquarters in Melbourne, Australia.
“There is a clear relationship between large igneous provinces and the world’s nickel, copper, platinum ore deposits,” Schissel reported last fall in a collection of research papers on the provinces.