image credit: Eurico Zimbres, Wikimedia Commons (taken at the San Diego Natural History Museum); image source; larger image

What Really Killed the Dinosaurs?

Dig into rocks around the globe at the right depth and you may find a thin layer like the one pictured above, a geological hint about our planet's past. This sedimentary layer contains much more iridium than the surrounding layers, and the element iridium is rarely found on Earth but plentiful in rocks in space. For this reason, some scientists believe that there was an enormous meteorite impact that covered the planet in its dust.

The iridium layer supports the impact catastrophe theory that dinosaurs of the late Cretaceous were killed by a meteorite impact and its ensuing planet-wide effects. However, new evidence suggests the crater thought to be responsible due to its iridium content (pictured at right) happened before the mass extinction. See What Really Killed the Dinosaurs? for more on the debate.

(This feature was updated on July 31, 2013.)

Login to Comment on this Item

Near Earth Object Program

Asteroids are usually shown between the orbits of Mars and Jupiter, but they also swing in as far as Earth's orbit, and frequently. At the time of this writing, astronomers have identified 1156 potentially hazardous asteroids, so-called because of their large size and close projected approach to Earth.

- To learn more about asteroid detection and impact risk, check out the NASA's Near-Earth Object Program.
- For daily updates about the Earth's local environment, read Spaceweather.com.

Advanced Search

Browse Physics To Go by Topic.

image credit: A. Hildebrand, M. Pilkington, and M. Connors; image source; larger image

Do We Know What Killed the Dinosaurs?

In the image above (upper left) you can see two concentric circles. These mark the location of the Chicxulub crater, and the white line shows the coast of the Gulf of Mexico. See this Canadian site (scroll down to the third image) for a fuller explanation of how the image was made and for related images.

(This feature was updated on July 31, 2013.)

- The Chicxulub crater is a candidate for the asteroid impact that killed the dinosaurs, but not all scientists are convinced. Some believe the iridium layer (pictured at left) could also have been produced by volcanic eruptions at the same time as the layer was created.  

- For more about the Cretaceous extinction and the debate over what caused it, see these articles from the University of California Museum of Paleontology and the Geological Society of America.

(This feature was updated on July 13, 2012.)

20 Ways the World Could End

There are many ways to destroy the Earth besides a meteorite impact. For a fun look at a few of these, see Discover Magazine's "20 Ways the World Could End." (Notably, an asteroid impact is number one on the list.)