The chances of the Earth's being hit by a meteorite are small at any given time, but they are greater than the chances of winning a lottery. The chances of dying from an impact are about the same as dying in a plane crash, for a person who takes one flight per year. These comparisons are statistical flukes, however, and reflect the fact that a large meteorite impact is likely to kill so many people that it raises the statistical chances of dying by impact. A globally catastrophic impact is generally thought of as one that kills more than 25 percent of the world's population, or currently about 1.6 billion people. The Earth has been hit by a number of small impacts and by some very large impacts that have had profound effects on the life on Earth at those times. Most geologists and astronomers now accept the evidence that an impact caused the extinction of the dinosaurs and caused many of the other mass extinctions in Earth history, so it is reasonable to assume that a large impact would have serious consequences for life on Earth. Nations of the world need to consider more seriously the threat from meteorite impacts. Impacts that are the size of the blast that hit Siberia at Tunguska in 1908 happen about once every thousand years, and major impacts, that can seriously affect climate and life on Earth are thought to occur about every 300,000 years. Events like the impact at Chicxulub that killed the dinosaurs and resulted in a mass extinction are thought to occur once every 100 million years. The Chicxulub impact initiated devastating global wildfires that consumed much of the biomass on the planet, and sent trillions of tons of submicrometer dust into the stratosphere. After the flash fires, the planet became dark for many months, the atmosphere and ocean chemistry were changed, and the climate experienced a short-term but dramatic change. The global ecosystem was practically destroyed, and one of the greatest mass extinctions in geological time resulted. Events that approach or exceed this size place the entire population of the world at risk and threaten the survival of the human species. Much smaller events have the potential to destroy agricultural produce in fields around the world, leading to an instant global food shortage and mass starvation, collapse of global economies, and political strife.
There are thousands of near-Earth objects that have the potential to hit the Earth and form impact craters of various sizes. Most of these objects are asteroids diverted from the main asteroid belt and long-period comets. A couple hundred of these objects are in Earth orbit-crossing paths. They range widely in size, density, and composition, all of which can play a role in the type of hazard the body poses as it enters the Earth's atmosphere and falls to the surface. In most instances, for objects greater than several hundred feet (~100 m) in diameter, size is the most important factor, and the controlling factor on the style and hazard of the impact is related to the kinetic energy of the object.
Different hazards are associated with large and minor impacts. Passage of atmospheric shock waves, followed by huge solid Earth quakes, is described, followed by analysis of the tsunamis generated by ocean-hitting impacts. The atmospheric fires associated with the impact, followed by blocking of the Sun by particulate matter thrown up by the impact and fires, is considered to be one of the most hazardous elements of impacts through which many organisms would struggle to survive.
Mitigation strategies for avoiding large impacts of asteroids with Earth involve first locating and tracking objects in Earth orbit-crossing paths. If a collision appears imminent, then efforts should be made to try to deflect the asteroid out of the collision
Was this article helpful?
Disasters: Why No ones Really 100 Safe. This is common knowledgethat disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.