one is impressed by the fact that
most of the surface features of the
Moon are shaped by impact craters.
The Earth is subject to more than
twice the amount of impacting events
than the moon because of its larger
size and higher gravitational attraction.
Yet, the Earth does not show a cratered
surface like the moon. The reason for
this is that the surface of the Earth
is continually changing due to processes
like erosion, weathering, tectonism,
sedimentation, and volcanism. Thus,
the only craters that are evident on
the Earth are either very young, very
large, or occurred on stable continental
areas that have not been subject to
intense surface modification processes.
Currently, approximately 200 terrestrial
impact structures have been identified,
with the discovery rate of new structures
in the range of 3-5 per year.
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been observed by Caucasians. Much of
our knowledge about what happens next
must come from scaled experiments. As
the solid object plows into the Earth,
it will compress the rocks to form a
depression and cause a jet of fragmented
rock and dust to be expelled into the
atmosphere. This material is called ejecta.
The impact will send a shock wave into
the rocks below, and the rocks will be
crushed into small fragments to form a
breccia. Some of the ejecta will be
hot enough to vaporize, and the heat
generated by the impact could be high
enough to actually melt the rock at the
site of the impact. The shock wave
entering the Earth will first move in
as a compressional wave (P-wave), but
after passage of the compressional wave
an expansion wave (rarefaction wave)
will move back toward the surface. This
will cause the floor of the crater to
be uplifted and may also cause the rock
around the rim of the crater to bent
upward. Faulting may also occur in
the rocks around the crater, causing
the crater to become enlarged, and
have a concentric set of rings.
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Magnitude 13, and numerous large
magnitude aftershocks would result
from the impact of a large object
with the Earth. The large quantities
of dust put into the atmosphere would
block incoming solar radiation. The
dust could take months to settle back
to the surface. Meanwhile, the Earth
would be in a state of continual
darkness, and temperatures would drop
throughout the world, generating global
winter like conditions. A similar effect
has been postulated for the aftermath
of a nuclear war (termed a nuclear winter).
Blockage of solar radiation would also
diminish the ability of photosynthetic
organisms, like plants, to photosynthesize.
Since photosynthetic organisms are the
base of the food chain, this would
seriously disrupt all ecosystems.
Widespread wildfires ignited by
radiation from the fireball as the
object passed through the atmosphere
would be generated. Smoke from these
fires would further block solar radiation
to enhance the cooling effect and further
disrupt photosynthesis. If the impact
occurred in the oceans, a large steam
cloud would be produced by the sudden
evaporation of the seawater. This water
vapor and CO2 would remain in the atmosphere
long after the dust settles. Both of these
gases are greenhouse gases which scatter
solar radiation and create a warming effect.
Thus, after the initial global cooling,
the atmosphere would undergo global warming
for many years after the impact. If the
impact occurred in the oceans, giant tsunami
would be generated. For a 10 km-diameter
object the leading edge would hit the seafloor
of the deep ocean basins before the top of
the object had reached sea level. The tsunami
from such an impact is estimated to produce
waves from 1 to 3 km high. These could easily
flood the interior of continents. Large amounts
of nitrogen oxides would result from combining
Nitrogen and Oxygen in the atmosphere due to
the shock produced by the impact. These
nitrogen oxides would combine with water
in the atmosphere to produce nitric acid
which would fall back to the surface as acid
rain, resulting in the acidification of surface
waters.
http://www.tulane.edu/~sanelson/Natural ... mpacts.htm
Earth was born as a result of repeated
asteroid collisions, the Moon was created
by a single giant (collission with Theia)
impact event. Then, Earth's size attracted
huge meteorites, which slammed into it,
causing super-high-temperature rock vapour
to cover the entire surface and evaporate
all ocean water. The earliest life-forms
survived such infernal events by escaping
deep into the ground, miraculously emerging
again and again. The Earth has gone through
innumerable catastrophic events, and life
has survived by acquiring new abilities to
live through each crisis. Humans are part
of the grand history of life's evolution,
which has been closely intertwined with
repeated cataclysmic events.
Learn what would happen if an asteroid hit
the Earth with this detailed "Large Asteroid
Impact Simulation." An asteroid with a diameter
of 500 km. Destination: The Pacific Ocean.
The impact peels the 10 km crust off the surface.
The shockwave travels at hypersonic speeds. Debris
is blasted across into low Earth orbit, and
returns to destroy the surface of the Earth.
The firestorm encircles the Earth, vaporizing a
ll life in its way. Within one day, the surface
of the Earth is uninhabitable. The evidence
shows that this has happened at least six times
in Earth's history. Music of Pink Floyd "The
Great Gig in the Sky" (1973).
0:12 An asteroid with a diameter of 500 km.
0:47 Destination: The Pacific Ocean.
1:17 The impact peels the 10 km crust off
the surface.
1:28 The shockwave travels at hypersonic speeds.
1:53 Debris is blasted across into low Earth orbit,
2:11 and returns to destroy the surface of the Earth.
2:55 The firestorm encircles the Earth,
3:05 vaporizing all life in its way.
3:34 Within one day, the surface of the Earth is
uninhabitable.
4:19 The evidence shows that this has happened
at least six times in Earth's history.
https://www.youtube.com/watch?v=bU1QPtOZQZU