METEORITIC IMPACT

The Earth has been getting hit by asteroids and comets for its whole life. The planets formed from collisions of smaller objects, and even our water may have come largely from comets.

To lead to a global catastrophe, an asteroid or comet only has to be big enough to launch large amounts of dust in to the atmosphere. That leads to the abrupt change in climate that wipes out species.

The odds of a major asteroid impact are very small. However, asteroids do pass close to earth, to have a major impact.

Impact event

An impact event is a collision between celestial objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal impact. When large objects impact terrestrial planets like the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry.

One of the best-known recorded impacts in modern times was the Tunguska event, which occurred in Siberia, Russia, in 1908.

The 2013 Chelyabinsk meteor event is the only known such event to result in a large number of injuries, and the Chelyabinsk meteor is the largest recorded object to have encountered the Earth since the Tunguska event.

Geological significance

Impacts have, during the history of the Earth, had a significant geological and climatic influence.

1.    Exogenesis-The origins of life may have been influenced by impacting objects by bringing organic chemicals or life forms to the Earth's surface

2.    Several consecutive impacts can have effect on the dynamo mechanism at a planet's core responsible for maintaining the magnetic field of the planet, and can eventually shut down the planet's magnetic field.

3.    an impact event in an ocean or sea may create a megatsunami (a giant wave), which can cause destruction both at sea and on land along the coast.

4.    The impact event can cause mantle plume (volcanism) at antipodal point

5.    Biospheric effects-The effect of impact events on the biosphere has been the subject of scientific debate. Several theories of impact related mass extinction have been developed.

Evidences for such an impact-Unusually high concentrations of iridium in a specific layer of rock strata in the Earth's crust. Iridium is an element that is rare on Earth but relatively abundant in many meteorites.

Multi directionally shocked quartz (coesite), which is only known to form as the result of large impacts or atomic bomb explosions, has also been found in the same layer at more than 30 sites. Soot and ash at levels tens of thousands times normal levels were found with the above.

Anomalies in chromium isotopic ratios found within the K-T boundary layer strongly support the impact.

6.    Sociological and cultural effects: End of civilization, An impact event is commonly seen as a scenario that would bring about the end of civilization. Read more...