Crater Diary, Part I

An aerial view of Meteor Crater, Arizona.
Credit: Jim Hurley, 1978

Every hundred thousand years or so, a large asteroid or comet hits the Earth. The explosive force of the impact sends tons of material into the air and punches a big hole in the crust. We don’t see a lot of these old craters, however, because Earth is a dynamic environment — wind, water, and tectonic plate shuffling constantly changes the appearance of the surface. Over time, many impact craters become altered or buried deep underground.

One such buried crater is underneath Chesapeake Bay in Virginia. Carved out 35 million years ago, the crater now can only be accessed by intensive drilling. In November, Aaron Gronstal, a microbiology student at the Open University in the United Kingdom, visited a drilling project at the Chesapeake crater. His goal: to discover what sort of microbes may now live deep underground in the ancient impact environment.

Crater Diary, Part 1
Exotic Life Beneath My Feet

November 14, 2005

I am currently standing in the middle of a soybean field on Eyreville Farm, located roughly four hours south of Washington D.C. on the eastern shore of Virginia. The soybeans are past harvesting, but it’s not this grassy plot of land at the Earth’s surface that interests me. I study microbes that live deep below ground in asteroid impact craters, and so I have come here to investigate the Chesapeake Bay crater.

chesapeake_credt: Aaron Gronstal
Sample team at work near Chesapeake site.
Credit: Aaron Gronstal

When people think of astrobiology research on Earth, they imagine scientists tromping around some of the harshest environments on the planet, searching for unique microbes called ‘extremophiles.’ Indeed, organisms that can live in harsh environments play a primary role in Earth-based astrobiology research, because they can teach us how life might survive on other planets in our solar system.

However, not all extremophile research takes place on expeditions to places like the Arctic, the Dry Valleys of Antarctica, or the high altitude lakes of the Andes. Extreme environments also can be found much closer to home — in this case, right beneath my feet.

The landscape of this particular section of the Chesapeake Bay area looks like a simple stretch of flat agricultural land, spread out between the waters of the bay and the Atlantic Ocean. But in fact, the mouth of Chesapeake Bay happens to be the location of an exceptionally large impact crater that was made by a comet or asteroid some 35 million years ago. The crater is more than 50 miles wide. Compared to other known craters in the world, its rank depends on how you chose to measure a crater’s size. Some say Chesapeake is the world’s sixth largest crater, others say it’s the seventh. To avoid causing any arguments, I’ll just say it’s pretty darn big.

chesapeake_credt: Aaron Gronstal
View of drilling unit, Chesapeake site.
Credit: Aaron Gronstal

The entire structure is now buried 300 to 500 meters beneath the ground, so it went virtually unnoticed until only a short time ago, when it was discovered by researchers from the U.S. Geological Survey (USGS) and the Virginia Department of Environmental Quality.

In recent years, drilling projects in the region have told us a great deal about the fantastic event that formed the crater, as well as the effect of the impact on the surrounding area. My task is to help complete the picture by examining how life today deals with the unique environment below the surface that was created so long ago by the massive collision.

I’ve traveled to Virginia from The Open University in the United Kingdom, where I am a student of Professor Charles Cockell at the Planetary and Space Sciences Research Institute (PSSRI). However, I was born and raised in Iowa. Although it’s well past the tourist season on the Virginia shore, it’s nice to be back in my home country for the Thanksgiving holiday.

I spent most of my first day on the drill site getting acquainted with the lab and sampling procedures. This specific drilling project, sponsored by the USGS and the International Continental Scientific Drilling Program (ICDP), is part of a larger effort to study the Chesapeake crater that has been going on for a number of years. There are a dozen or so holes that have been drilled in and around the crater, but the site where I’m standing now is special because of its location. Just north of the small town of Cape Charles, this site is on the central uplift of the crater — a mass of Earth that ‘bounced back’ after the asteroid struck the planet.

The goal of this drilling project is to dig all the way to the basement of the crater itself. This is far deeper than any of the previous holes, and will allow scientists to characterize the crater from the surface all the way down to the bottom.

chesapeake_credt: Aaron Gronstal
Keeping track of drilling depth.
Credit: Aaron Gronstal

I asked the geologists how they would know when they hit the bottom of the crater. The truth is, it’s difficult to tell. From their seismic data, they estimate the basement is less than, but close to, two kilometers (1.2 miles) down. The seismic data isn’t accurate enough to tell for sure though. The hope is that around two kilometers they’ll hit very solid basement rock, and the rock will then just continue down as such.

Before I arrived, the team got stuck in a 900-foot block of solid granite. When they first hit the granite, some of the researchers thought they had reached the crater basement. But now the drill has moved out of the granite and into a softer material called ‘suevite.’

Drilling through granite is a very slow process, and after a few weeks everyone had grown tired of it. Granite wasn’t particularly interesting for the geologists, and nearly impossible for the biologists to sample.

They’ve drilled down 4,748 feet, and everyone is hoping we’ll be able to reach a mile (5,280 feet) within the next week. Everyone is excited at the prospect of bringing up the ‘mile stone.’ This would be a huge emotional achievement for everyone involved, and it would also help ensure financial support for the project until the basement of the crater is reached.

After my introduction to the site and safety procedures, there was some additional excitement. Virginia may not be a particularly remote and dangerous location compared to other astrobiology expeditions, which take place in regions where you might have to fend off hungry polar bears looking for their next meal. But we do have puppies. Before my arrival, the drillers working on the site adopted a stray German Shorthaired Pointer named Gunner who had been roaming the area. She was a bit thin, but began to plump up after some good, hearty feeding. The plumping continued…and continued…and in the end she produced a litter of 10 adorable pups. So in addition to their regular work at the site, the drillers and scientists have been trying to find homes for the puppies.

The search for owners was successful, and this evening everyone bid farewell to the cute little guys and girls. Gunner and one of her puppies are going home with one of the drillers, who is leaving the project tomorrow. Apparently he and Gunner hit it off immediately. He had even bought her a little doghouse to put next to the drillers’ trailer.

Read Part 2
Read Part 3
Read Part 4