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.)
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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.