WASHINGTON—Scientists on drill ships are studying colossal slabs of volcanic lava hidden under the sea that shaped its climate, helped determine its life forms and record Earth's violent past.
They think their research can help explain what's happening to our warming world today.
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's now the Atlantic Ocean stretch across four continents, in places ranging 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 dry land, these belches from the planet's fiery interior contributed to a series of mass extinctions of most of the organisms that were then alive.
Although the extinctions were devastating to life at the time, scientists think they opened the way for new, more advanced creatures to evolve, including ourselves. Without them, we wouldn't be here.
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, however, 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 said in an e-mail message. "The consequence of rapid warming of oceans and atmospheres appears to be mass extinction."
Lava is a common type of rock that's been melted by temperatures as high as 2,000 degrees Fahrenheit and flows out from a volcano or a crack in the 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 said in an e-mail interview, and "almost certainly played an important role in bringing about these extinctions."
The oceanic lava sheets are mostly 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 volcanic eruptions, averaging about 600,000 years apart. The latest 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.
According to Hyndman, Yellowstone is sitting on a rising plume of molten rock—like a gigantic lava lamp—from below the Earth's surface. The plume makes the park floor bulge above the surrounding landscape. The heat from below drives hot springs and geysers, such as Old Faithful.
The last Yellowstone eruption dwarfed more recent volcanic events, such as Krakatoa in 1883 or Mount St. Helens in 1980. It was greater than a monster blast at Tambora in Indonesia in 1815 that killed about 100,000 people. Tambora's gas and dust circled the Earth, leading to a fabled "year without a summer" in North America, crop failures and food riots in Europe.
In another example, a mile-and-a-half-thick layer of lava, known as the Deccan Traps, flowed across a large part of India 65 million years ago. Its toxic emissions probably weakened the dinosaurs before the impact of a huge meteor finished them off, French scientists reported in the Aug. 12 edition of the journal Science.
Although geologists have known about the lava provinces for decades, many questions remain about these extraordinary structures. More of them 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, according to Don Schissel, an executive with BHP Billiton, a global mining company headquartered 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.
For more information online, go to www.largeigneousprovinces.org
(c) 2005, Knight Ridder/Tribune Information Services.
Need to map