35-mln-yr old impact may have created a new niche for life deep undergroundJune 27th, 2008 - 12:17 pm ICT by ANI
London, June 27 (ANI): Geologists have suggested that a violent impact that gouged out a 90-kilometre-wide crater in the US state of Virginia 35 million years ago, may have created a new niche for life deep underground.
According to a report in New Scientist, hidden by younger sediments, the Virginia crater, known as the Chesapeake Bay Impact Structure, is among the worlds largest and best-preserved craters.
Now, Gregory Gohn of the US Geological Survey in Reston, Virginia, and colleagues have drilled nearly 2 km into the basin to reveal its formation.
They believe that a 2-km-wide object hurtling faster than 10 km per second crashed into 200 to 300 metres of water covering soft sediments and layers of hard rock on North Americas continental shelf.
The kinetic energy of the impact is just off the scale by anything humans can relate to, Gohn told New Scientist.
The impact formed a transient crater about 20 km wide and 7 km deep. Within 20 seconds, the shock spread a giant wave of debris including shattered rocks and water outwards, where some of it fell into the sea.
The transient craters walls began slumping inwards about 40 seconds after impact, triggering a landslide that sent a megablock of granite 275 m thick into the crater.
About 6 minutes after impact, water that surged away from the impact zone rolled back into the steaming hole, carrying ejecta splattered from the crater and sediment torn up from the sea floor.
Debris blasted into the air rained back to the surface.
By 10 minutes after the impact, slumping walls had left the crater, which was full of churning water and sediment, about 38 km wide. Another ring of debris settled in the ocean about 40 km from the craters centre.
The impact probably heated the area to 350 degC, killing off any life.
But the team has found living cells at depths of more than 1.4 km, in regions where rocks appear to have been broken up by the impact or its aftermath.
According to team member Mary Voytek of the USGS, some rocks were also shocked, which made them more crumbly.
Such fragmentation and crumbling provided larger spaces that organisms could move into, Voytek told New Scientist.
Furthermore, the violence of the event moved carbonaceous material from plant and other forms of life from the surface down to great depths, and flushed oxygenated water, which organisms use to breathe, downwards as well.
Its almost like mixing in some compost into a garden. The further you work it into the soil, the better you make it for the organisms, said Voytek. (ANI)
Tags: chesapeake bay, continental shelf, craters, degc, ejecta, giant wave, impact structure, impact water, impact zone, kinetic energy, megablock, new scientist, reston virginia, sea floor, soft sediments, state of virginia, transient crater, underground london, us geological survey, violent impact