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[escepticos] Impactos y civilizaciones



    No me lo acabo de creer mucho pero...

    Saludos

    Mario

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<<Lo menos que podemos hacer, en servicio de algo, es entenderlo>>

Ortega y Gasset


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http://www.spacedaily.com/spacecast/news/deepimpact-00a.html

Impact Events Shaped Rise Of Civilization
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Liverpool - March 7, 2000 - In a presentation to the Annual Meeting of the
American Association for the Advancement of Science (AAAS), Dr Benny Peiser
of Liverpool John Moores University, presented new evidence suggesting that
more than 500 impact events of extraterrestrial orgin have punctuated Earth
during the last 10,000 years.
The great majority (70%) of these events have been of the Tunguska-type
class of atmospheric impacts with an average energy yield of between 20 and
100 Mt TNT. However, more than 100 surface impacts, including more than a
dozen oceanic impacts, are believed to have repeatedly devasted whole
regions, small countries and early civilisations around the globe.

In a worst case estimate, Dr Peiser said that up to eight climatic downturns
detectable in the geological and climatological records of the Holocene may
be directly associated with multiple impact events.

"Episodes of increased cometary or meteoric activity punctuating societal
evolution should be looked upon as potential agencies determining the rise
and fall of ancient civilisations.

Both the emergence and the collapse of human cultures, the
Pleistocene-Holocene transition and the Neolithic Revolution, the onset and
collapse of the Bronze Age civilisations, and even the collapse of the Roman
Empire may be associated with episodes of increased cosmic activity and
multiple impacts that may well have included incidents of cosmic dust
loading."

While most of these impacts occurred over unpopulated areas of the globe,
there are historical accounts about devastating cosmic catastrophes.
According to a number of Chinese records, about 10,000 people were killed in
the city of Chi'ing-yang in 1490 AD due to the break-up of a small asteroid.

About a dozen hypervelocity impact craters that date from the Holocene
period (i.e. since the end of the ice age) have been discovered to date. The
majority of impacts, however, that occurred during this crucial period of
societal evolution have not been detected yet.

According to Dr Peiser, "the 14 known Holocene impact craters most certainly
paint a rather deceptive picture of our past. The fact that no massive
impact crater dating to the Holocene has been detected, has led to the
belief that no hemispheric or global impact disaster can possibly have
happened. However, this is a widespread delusion."

Yet there still is a regretable lack of interest by the scientific community
to scrutinise the Holocene for major impact events.

"The widespread ignorance of such cosmic disasters in historical time is due
to the limited research focus on crater producing events. Yet only 3% of
fatal impacts produce a hypervelocity surface crater on land", Dr Peiser
points out.

Tunguska-like impacts or "Super-Tunguskas" are thus taken out of the
equation. Due to their catastrophic detonation above ground (or in the
oceans), they often leave no obvious fingerprints behind.

Dr Peiser also presented new impact simulations that estimate expected
fatalities of cosmic impacts for the next 10,000 years. Without the
establishment of effective strategies of planetary defense in the future,
more than 13 million people are expected to die as a direct result of impact
catastrophes in the next ten millennia.

"We can, and indeed have to live with smaller, Tunguska-type impacts. There
is little we can do about them. But we need to prevent the impact of larger
objects which threaten the stability of our civilisation.

"Unless we start planning ahead and develop the technology for the
deflection of this threat, cosmic impacts will inevitably lead to major
disasters in the future", Dr Peiser stressed.

Based on computer simulations that take into account the current flux of
near-Earth objects, a typical 10,000 years period with a constant human
population of 5 billion can expect to experience: *110 fatal impacts
resulting in a total of 13 million fatalities (an average of 120,000
fatalities per event).


300 "Tunguska" style airbursts over land, with 80 of these producing
fatalities (roughly 1 fatal event per century).
12 ocean impacts that produce tsunami, with an average of 500,000 fatalities
per event.
4 land impacts, with an average of 500,000 fatalities per event.

"These estimates are based on the assumption that the current asteroidal and
cometary flux will be constant in time and quantity over the next 10,000
years. However, there is growing evidence to suggest that there have been
peak levels of meteoritic activity in the past that differed significantly
from the cosmic calm of the last 300 years", Dr. Peiser pointed out.
In January, a UK Task Force was set up by Lord Sainsbury, the Science
Minister, to look into the way in which Britain should respond to the impact
hazard and how it can contribute to the international efforts prevent major
impacts from happening in the future.