What Killed the Dinosaurs?

Paleontologists have long searched for clues as to what caused the mass extinction of the large dinosaurs. How did hundreds of species vanish so abruptly, leaving us only their fossilized remains as clues that they ever existed? Such a devastating event would have required a sudden onset of dramatic changes in the Earth’s climate.

This event in time is known as the K-Pg boundary, or the Cretaceous-Paleogene boundary, a marker between an era when dinosaurs roamed the Earth and a world more like today. We can trace the Earth’s history to study this time period by delving into deeper and deeper rock layers which each carry an imprint of the events that occurred when those rocks were once at the surface. The thin layer of rock at the K-Pg boundary marks the end of the Mesozoic Era and, along with it, the end of most of the Mesozoic species, including all non-flying dinosaurs.

Believe it or not, we are still learning new things from these ancient rocks, both as scientists discover new sites and see technological improvements in the equipment used to study them. Already this year, two exciting results have weighed in on two possible causes for the abrupt climate change at the K-Pg boundary: volcanoes and asteroids. So, how did the dinosaurs meet their end?

The large cloud of dust kicked up by the impact would have been thick enough to coat the planet and block out sunlight, first killing off plants, then the animals that fed on plants, then the animals that fed on those animals.

Evidence for an Asteroid Impact

An asteroid impact, given a large enough asteroid, could have caused fast and thorough devastation. The large cloud of dust kicked up by the impact would have been thick enough to coat the planet and block out sunlight, first killing off plants, then the animals that fed on plants, then the animals that fed on those animals. 

There are four leading pieces of evidence that suggest a massive and dramatic asteroid impact led to the dinosaurs’ demise:

• First, a massive crater believed to mark the asteroid’s impact, known as the Chicxulub Crater, has been found buried underneath the ground in the Yucatan Peninsula in Mexico. The asteroid big enough to make the crater would have been ~7 to 50 miles across and would have dated back to precisely the time of the fall of the dinosaurs. 

• Second, sand that originated in the ocean is found deposited around the Chicxulub Crater, which is consistent with a giant tsunami, which would have been triggered by an impact, carrying the sand inland. 

• Third, elements like...

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