Cracking Open a Vault

chesapeake_credt: Aaron Gronstal
Checking out a drilling core. Click image for larger view.
Credit: Aaron Gronstal

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. This portion of his journal is part 2 of a 4-part series.

Read Part 1

Crater Diary, Part 2
Cracking Open a 35-Million-Year-Old Vault

November 15, 2005

Today was my first full day on the drill site, and also my first as an official member of the ‘day shift’ (noon to midnight). The drilling site consists of an 80-foot tall drilling rig, a trailer for the researchers, a trailer for the drillers, and a small collection of portable toilets. The women, for some reason, have seized exclusive use of the toilet next to the research trailer.

chesapeake_credt: Aaron Gronstal
Hard at work on a sunny day. Click image for larger view.
Credit: Aaron Gronstal

I spent much of my day trying to familiarize myself with my surroundings, perusing the posters and news articles pinned to the walls inside the trailer, or reading sampling procedures and lab notebooks.

There are typically about five or six people working on an average shift, and most of the time I’ll be the only biologist on site. The other researchers are geologists, paleontologists and hydrologists. There’s also the odd physicist or two, but geologists definitely have the advantage in numbers.

My job is to collect biological samples from the deep subsurface of the Chesapeake crater. When the drilling team brings a core of rock and sediment to the surface, I’ll collect pieces of the core and eventually take them to a laboratory for further analysis.

The obvious question people ask when I discuss this research is, "What are you looking for?" The first thing to make clear is that we are NOT looking for alien life that was transported to Earth on an asteroid. That, of course, would be very interesting, but it is also extremely unlikely!

Instead, we are trying to understand the different terrestrial bacteria that are able to live in the environment created by the impact. We hope to be able to identify the bacteria living at various depths in the crater, and determine the methods they use to survive in such a unique environment.

When the Chesapeake crater was created, a large comet or asteroid collided into what was then shallow coastal water. The impact punched a large hole in the ground and sent up massive tsunami waves 2,000 feet high. The waves flooded back into the newly formed crater, and dragged a huge amount of debris from the surrounding area along with them. This included rocks, mud, plants, animals, bacteria, and whatever else the water happened to wash over. All this material was then covered by a layer of sediments, which has preserved the material up to the present day. Beneath this protective layer, there may be remnants of a world long gone that could tell us a great deal about the history and evolution of our planet.

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

The possibility of having a ‘vault’ of 35 million-year-old material is exciting, and this current drilling project should allow scientists to determine whether or not this is actually the case. I’m not looking for fossils, but the paleontologists working on the crater are looking for diatoms (microfossils). Searching for anything bigger would require a fairly large-scale excavation.

If there are bacteria currently living deep below the surface, they’re living in sediments that were altered by impact pressures and heat. They are also soaked in the extremely salty ground water in the crater today. By looking at microbes in this system, we will be able to study the long-term effects that an impact can have on the habitability of an environment, as well as life’s ability to re-colonize after an impact event.

There have been plenty of studies concerning subsurface bacteria, but this is the first time microbes have been studied while drilling an impact crater. In subsurface environments you usually see a gradual decline in the number of microbes in the soil the deeper you go, until you reach a point where the geothermal heat is too intense for them to survive. We’re hoping to determine if an impact event can alter the environment enough to change this distribution of microbes. From what we know about the crater so far, it seems to be a very unique environment, so it’s difficult to make any guesses as to what we may find.

At the moment, the drill cores from the crater are coming up regularly and in rather large pieces — some of them are 20 feet long. The level of excitement at the site is high, and the 900-foot block of granite is becoming a distant memory. Suevite continues to come up from the drill hole, and everyone is eagerly awaiting each core that the drillers bring to the surface. The drillers themselves, however, seem unfazed by the excitement. I suspect they miss the puppies.

November 16, 2005

When I first arrived here, I managed to snag a bed in a house with the geologists. It’s in a new Cape Charles housing development, and located only about five miles from the drilling site. In comparison to other field expeditions I’ve been on in the past, the conditions are excessively posh. We have a hot shower and a television where I can catch up on The Daily Show. It’s a large house, enough to accommodate the two shifts of scientists and the occasional freeloading researcher who sleeps on the couch (which of course, would have been me if I hadn’t arrived early enough to grab the last available bed).

chesapeake_credt: Aaron Gronstal
Drilling unit at night.
Credit: Aaron Gronstal

Today, after a few pots of coffee, I arrived on the drill site just as a core was being brought to the surface — perfect timing for some early morning sampling. But then small problems arose in the lab. The vacuum sealer refused to function properly, and a sealed sample bag decided to blow itself up like a balloon when it was removed from the liquid nitrogen tank. These issues were straightened out quickly, however, and everything was running in normal order before lunch.

For the rest of the day, the cores being brought to the surface were small — only about three or four feet each, so progress toward the floor of the crater was slow. Sampling times for the biology experiments were also few and far between, leaving plenty of time for chewing on fingernails, wondering if we’ll make it to the crater floor before the funding runs dry.

Aside from the difficulties sampling, the weather lent an ominous tone to the drill site. It was unseasonably warm — almost muggy, in fact — and the air conditioning was pumping away all day inside the trailer. But thick clouds were pushing seaward, and was predicting a drastic change in conditions. A sizeable storm brewing overhead would dash my plans of returning to England with a nice tan.

By the day’s end, flashes of lightning could be seen in the distant sky over Chesapeake Bay. There was a tense feeling in the air — we have a towering metal drilling rig positioned in the center of our soybean field, secured with metal guidelines, so lightning would put an end to the night’s drilling, further hindering progress toward the crater floor. We tried to frequently check the online forecasts, but as the sky continued to grow heavy with clouds, the satellite connection had the speed and convenience of dial-up.

The storm finally hit us after dark, rolling in with howling winds that rocked the trailer back and forth. This was followed by spitting rain, and distant thunder added a dramatic effect. Luckily the lightning stayed away, so drilling continued under the safety of yellow rain jackets and hoods pulled tight about the ears. Running around in the wind and rain, and struggling to force the trailer doors shut against the strong gusts with stiff, shivering hands managed to keep us all awake to the end of the shift. Stormy weather makes everything more exciting.

Read Part 1
Read Part 3
Read Part 4