Crater study surprise

Deep in ground where meteorite hit, rocks are full of extra-salty water

June 27, 2008|By Dennis O'Brien | Dennis O'Brien,Sun reporter

Scientists drilling into the site where a giant meteorite smashed into the lower Chesapeake Bay millions of years ago have found one more surprise amid the microscopic life and pockets of prehistoric ocean.

The water is saltier than expected - and no one is sure why.

"It's not a reservoir. It's water in pores and in cracks and shattered rocks," said Ward Sanford, a hydrologist with the U.S. Geological Survey.

Scientists have been examining the bay impact crater since its discovery in 1993.

Today, they published in the journal Science the report on core samples extracted from this mile-long shaft - the deepest so far.

The analysis sheds light on how the meteorite that struck Earth 35 million years ago created habitats conducive to microscopic life, according Greg Gohn, a researcher at the U.S. Geological Survey and the report's lead author.

"We're looking at all of the effects of these impacts," he said.

Water as salty as that which researchers found at the drill site has been extracted from sites in Maryland and North Carolina over the years, but it was from much lower depths in those locations, Sanford said.

At the crater site, the impact may have brought briny water closer to the surface, he said.

After the meteorite hit, subterranean water, rock and sediment rose up and then settled into cavities like cereal poured back into a box, Sanford said.

It could be that salty water from deep inside the planet rose up as the debris resettled, he said.

Tests on salinity of the water show it is twice as salty as sea water but poses no immediate danger to the groundwater supplies of nearby Newport News and other Virginia Tidewater communities, the researchers say. The sediments are too thick to let it pass, Sanford said.

"It takes a long time for the saltwater to move that far. And water doesn't flow through those sediments that easily," he said.

The effort to study the Chesapeake Bay impact crater is a work in progress. An international team of 40 scientists will continue testing the shattered rocks, sediment and microbes in core samples extracted on a privately owned farm five miles north of Cape Charles, Va., between July and December 2005.

But so far, scientists say evidence in the shattered and superheated rocks and sediments shows that when the mile-wide meteorite splashed into the underwater coastal plain, it created a tsunami that threw vapors into space, incinerated everything in its path and sent shattered rocky material flying for thousands of miles.

"It would've been a huge splash," said David A. Kring, a Houston-based crater expert at the Lunar and Planetary Institute, who reviewed the report but was not a part of the study.

The bay crater is the largest in the United States and by some estimates the sixth-largest in the world.

The meteorite that formed it helped shape the bay, continues to affect water supplies in surrounding Virginia communities and is used by teachers in Maryland and elsewhere to spark interest in geology.

"It's very exciting stuff," said Rachel Burks, a geology professor who lectures on the crater to students at Towson University.

The $1.5 million drilling project confirmed that the meteorite's impact created a "sterilizing pulse" that wiped out most of the microbial life at depths below 2,600 feet, said Mary Voytek, a USGS biologist.

Nutrients created by animals and plants wiped out by the blast were washed down into a cavity formed by the impact. Shock waves from the impact created pore-filled rock and sediments, Voytek said. The result: nooks and crannies at depths below 4,600 feet that harbor more mysterious microscopic organisms than anyone expected.

"What happened is, you've created a nice little incubator for life," she said.

The researchers had planned to drill 7,200 feet. But a huge granite slab, dislodged by the impact 35 million years ago, limited their progress to a little over a mile, roughly 1,400 feet short of the goal.

"Ideally we would've wanted to go deeper, and if we hadn't had to slow down, we would have," Gohn said.

Researchers say impact craters can reveal clues about prehistoric conditions that spawned some of the earliest forms of life on Earth. Drilling can shed light on the size of the meteorite, how hard it struck and what it did to the planet, scientists say.

"What is the consequence of a meteor impact? Does it sterilize the crater area and, if it sterilizes things, how quickly do microorganisms repopulate the crater fill material?" said David Vanko, a geology professor at Towson University.

Vanko, who helped collect and classify core samples, plans to publish findings next year on the heat and geothermal energy from the impact, based on analyses of melted and crystalline rocks.

Prehistoric Eearth was probably pelted by millions of meteorites, said Kring, of the Lunar and Planetary Institute. He oversaw drilling in 2001 into the Yucatan peninsula crater, where scientists believe a meteorite struck 65 million years ago, leading to dinosaurs' extinction

For corroboration, he and others look to the moon, where evidence of up to 400,000 impacts is visible on the surface.

But researchers have discovered only 170 craters on Eearth because the planet's surface is continuously being churned up by plate tectonics, erosion and other geologic and climatic conditions, Kring said.

Scientists spent 21/2 months drilling into the Yucatan crater - and then spent six years studying the core material, he said.

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