GEOLOGIC HISTORYThe Last 4.6 Billion Years

M O N T H L Y N E W S L E T T E R

D i s a s t r o u s D r o u g h t s !

What caused the extinctions of these amazing creatures? What would the world be like if they were still here?

ASTEROID OF DOOM?

he asteroid collision theory, which was brought to wide attention in 1980

by Walter Alvarez and colleagues, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez et al. proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact.[120] The bulk of the evidence now suggests that a bolide 5 to 15 kilometers (3 to 9 mi) wide hit in the vicinity of the Yucatán Peninsula (in southeastern Mexico), creating the

approximately 180 km (110 mi) Chicxulub Crater and triggering the mass extinction.[121][122] Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave. The

240 mya

Earliest Dinosaurs

215 mya

Hello mammals!

160 mya

Abundant Dinosaurs

146 mya

Earliest Birds

65 mya

Mass Extinction

How did it end? According to Wikipedia...

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Mass

Extinction

Time Line

Would it be possible to bring them back? Good idea? Bad idea?

consensus among scientists who support this theory is that the impact

caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun). Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid, being down to hours rather than years.[123]

In September 2007, U.S. researchers led by William Bottke

of the Southwest Research Institute in Boulder, Colorado, and Czech scientists used computer simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that a giant asteroid named Baptistina, approximately 160 km (99 mi) in diameter, orbiting in the asteroid belt which lies between Mars and Jupiter, was struck by a smaller unnamed asteroid about 55 km (35 mi) in diameter about 160 million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the Baptistina family. Calculations indicate that some of the

fragments were sent hurtling into earth-crossing orbits, one of which was the 10 km (6.2 mi) wide meteorite which struck Mexico's Yucatan peninsula 65 million years ago, creating the Chicxulub crater.[124] In 2011, new data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub Crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.[125]

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