June 23, 2006 — Scattered rafts of black lava over northern and central Australia are really part of one gigantic volcanic field that appears to be one of oldest and largest on Earth, say geologists.
If so, the half-billion-year-old eruption might be the culprit in the first mass animal extinction event in the history of life.
Australian geologists used both the chemical signatures of the far-flung basalt lava rocks and their ages to connect them to a single huge volcanic eruptive episode between 505 and 508 million years ago.
The newly identified Kalkarindji Continental Flood Basalt Province covered at least 400,000 square miles with more than 120,000 cubic miles of lava, report geologists Linda Glass and David Phillips of the Australian National University.
"It may be a lot larger than we think," Phillips told Discovery News. That’s because ever since their paper in the June issue of Geology hit the web, he’s been getting calls from other Aussie geologists who say they know of even more distant pieces of what could be the same mega lava deposit.
Unlike episodic and hacking explosive volcanoes like Mount St. Helens or Mount Pinatubo, flood basalts literally pour lava out onto the Earth’s surface in often vastly greater quantities and over far longer periods — perhaps many hundreds of thousands of years, according to some geologists. That means they can cover a lot more ground.
Younger recent flood basalts can be found mostly intact in places like the Columbia River region of the US Pacific Northwest. But at a half-billion years old, the Kalkarindji Continental Flood Basalts have been heavily eroded and buried — leaving only far-flung hints of its former glory.
"This is part of a growing picture," says Paul Renne, director of the Berkeley Geochronology Center in California.
Other large volcanic provinces have been identified in the same way — first in one area by a few geologists, then with a flurry of discoveries by other geologists who were working on other parts of the puzzle, but hadn’t seen the larger context.
Two things make the Kalkarindji Continental Flood Basalt Province discovery special and robust, says Renne.
One is that it’s the oldest such lava formation dated using the very reliable Argon-40/Argon-39 analysis, and Phillips is one of the world’s top "Argon-Argon" researchers, said Renne. Still, Renne adds that chemical aging of the far-flung rocks makes the process of dating them slightly less reliable.
The second thing is that the timing of Kalkarindji is right at the first major die-off of animals after they first exploded onto the scene about 535 million years ago during the Lower Cambrian Period.
"That time span was when (animal) life on Earth really took off," says Phillips. "We have the mass proliferation of species."
"Things just took off like wildfire," agrees Renne. Then at somewhere around 500 million years ago many of the strange new beasts were mysteriously wiped out.
A massive release of lava could have caused such an event by releasing a lot of heat and climate changing gases into the atmosphere.
