The true
impact of an asteroid or comet crashing near the Chesapeake Bay 35 million
years ago has been examined in detail for the first time. The analysis reveals
the resilience of life in the aftermath of disaster.
The impact
crater, which is buried under 400 to 1,200 feet (120 to 365 meters) of sand,
silt and clay, spans twice the length of Manhattan. The sprawling
depression helped create what would eventually become Chesapeake Bay. About
10,000 years ago, ice sheets began to melt and once-dry river valleys filled
with water. The rivers of the Chesapeake region converged directly over the
buried crater, according to the U.S. Geological Survey (USGS).
Gregory
Gohn of the USGS and his colleagues analyzed samples from two deep holes
drilled into the crater near its center.
"I
think what we wanted to do is drill into the central part of the crater and get
as long of a section as we could and understand the processes that put them in
the order we found them," Gohn told SPACE.com.
Within
seconds of the object's touchdown, rocks were flung high into the air. The
force of the impact carved a colossal cavity and caused temperatures to
skyrocket, turning brittle rocks into taffy. Then, material along the cavity's
rim surged downhill into the bowl-shaped depression like an avalanche.
The extreme
heat, the researchers say, killed off most life. However, they found abundant
microbes living today in the deepest parts of the crater. Some of the ancient
bacteria would have survived the impact, the researchers say, because their
little hideouts didn't feel the brunt of the heat. The rest of the abundant and
newly discovered microbial life is thought to have recolonized the zapped area
possibly tens of thousands of years following the impact when temperatures
dropped to habitable levels.
"The
impact broke up and disaggregated all of these blocks of rock," said researcher
Mary Voytek, a microbiologist at the USGS, "and that actually creates
space for [the microbes] to colonize and it also creates new routes for water
and material to move though, which is always good for bugs."
So a catastrophic
event like this could actually be a boon to microbes, at least in the
long-run, Voytek said. The impact breaks up compacted rock to create nooks and
crannies for bacteria to reside in, and it also brings in a fresh supply of
food.
"It's
somewhat analogous to whale falls," when a whale carcass eventually
settles on the sea floor, Voytek said. "All of a sudden it's a restaurant
for these bugs."
Understanding
the biological effects of this asteroid impact will shed light on the potential
for life deep underground during Earth's Archaean period, 3.8 billion to
2.5 billion years ago, when impacts were more frequent than today. The results
also have implications for predicting life in the deep biosphere on Mars.
"If
we're going to find life [on Mars], everyone agrees a good place to look is in
the subsurface," Voytek said.
The project, which is detailed in the June 27 issue of the journal Science, was funded by the USGS, NASA, the National Science Foundation, the Austrian
Science Foundation and DOSECC Inc.
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