Notable Asteroid Impacts in Earth’s History

The Chicxulub Event

65 million years ago an asteroid roughly 10 to 15 kilometers (6 to 9 miles) in diameter hit Earth in what is now Mexico. The impact killed 70% of all species on Earth, including the dinosaurs.

An impact of that size would have had devastating effects, and the geological record gives us some indication of what happened. The asteroid hit in water, creating mega-tsunamis reaching from southeastern Mexico all the way to Texas and Florida and up a shallow interior ocean that covered what is now the Great Plains. The blast would have thrown chunks of the asteroid and Earth so far that they would have briefly left the atmosphere before falling back to the ground.

Like millions of shooting stars, all this material would have been heated to incandescence upon re-entry, heating Earth’s surface and igniting wildfires. It is possible that all of Earth’s forests burned. Meanwhile, colossal shock waves would have triggered global earthquakes and possibly volcanic eruptions. A cloud of super-heated dust, ash and steam would have spread from the crater as the impactor slammed underground in less than a second. This dust could have covered the entire surface of Earth for up to a decade, creating a harsh environment for living things. Perhaps more significantly, the dust could also have lingered in the atmosphere, blocking out the Sun and interrupting the photosynthesis of plants that the entire food chain depends on, as well as cooling the temperatures of the Earth for many years.

The Next Event?

Although immense impactors like the one that devastated the entire planet 65 million years ago are rare, NEOs of many different sizes can pose serious threats. An impact on or over a densely populated city could cause millions of deaths, and an impact on water could cause massive flooding on coastlines. Any major impact would lead to widespread damage, injury, and death, and would create unparalleled humanitarian and refugee crises around the world.


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