[astroCS] Antarktidu zasiahol pred 780 000 rokmi asteroid!

[Marek Husarik]

   http://www.guardian.co.uk/uk_news/story/0,3604,1285889,00.html

Scientists using satellites have mapped huge craters under the Antarctic ice
sheet caused by an asteroid as big as the one believed to have wiped out the
dinosaurs 65m years ago.

Professor Frans van der Hoeven, from Delft University in the Netherlands,
told the conference that the evidence showed that an asteroid measuring
between three and seven miles across had broken up in the atmosphere and
five large pieces had hit the Earth, creating multiple craters over an area
measuring 1,300 by 2,400 miles.

The effect would have been to melt all the ice in the path of the pieces, as
well as the crust underneath. The biggest single strike caused a hole in the
ice sheet roughly 200 by 200 miles, which would have melted about 1% of the
ice sheet, raising water levels worldwide by 60cm (2ft).

But the climatic conditions were different at the time of the strike - about
780,000 years ago - from when the asteroid that is believed to have wiped
out the dinosaurs struck Yucatan in Mexico.

That impact created dust storms and fires that, by blocking out the sun,
cooled the Earth's atmosphere so much that the dinosaurs could not survive.
The Antarctica strike occurred during an ice age, so even tidal waves would
have been weakened to mere ripples by the calming effect of icebergs on the
ocean.

Prof Van der Hoeven first realised that there may have been a giant asteroid
strike in the Antarctic while on an expedition across the continent in 1960
when he noticed severe anomalies in the gravity from the rocks below,
indicating a crater. By coincidence another scientist had concluded that a
giant event must have occurred around 780,000 years ago somewhere in the
southern hemisphere, probably Antarctica.

But it was not until this year, when two satellites operating above
Antarctica began to map the anomalies in the gravity, that the scale of the
crater emerged. The mapping showed that the holes in the rock created by the
strike had refilled with a mixture of ice, rock and other debris far less
dense. This material, called breccia, shows where and how deep the craters
are.

Prof Van der Hoeven said: "The extraordinary thing about this meteor strike
is that it appeared to do so little damage. Unlike the dinosaur strike there
is no telltale layer of dust that demonstrates the history of the event. It
may have damaged things and wiped out species but there is no sign of it."

One thing that did happen at exactly the same time was the reversing of the
Earth's magnetic field. There is no other explanation as to why this took
place and Prof Van der Hoeven believes it was caused by the impact.



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