The element found in significantly high concentrations at the K-T boundary, now officially known as the Cretaceous-Paleogene (K-Pg) boundary, is iridium.
This distinct layer of iridium is a crucial geological marker, globally recognized for its elevated levels of this rare element.
The Significance of Iridium at the K-T Boundary
The K-T (or K-Pg) boundary represents a pivotal moment in Earth's history, approximately 66 million years ago, marking the end of the Cretaceous period and the beginning of the Paleogene period. This geological stratum is most famous for signaling the mass extinction event that wiped out the non-avian dinosaurs and a vast number of other species.
Across the globe, from Europe to North America and beyond, geological formations at the K-T boundary consistently exhibit an anomalously high concentration of iridium. This iridium layer has been identified in over 100 different locations worldwide, both on land and beneath the ocean.
Here's why iridium is so significant at this boundary:
- Rarity on Earth's Surface: Iridium (Ir) is a platinum-group metal that is exceedingly rare in the Earth's crust. It is much more abundant in the Earth's core.
- Abundance in Extraterrestrial Objects: Conversely, iridium is found in much higher concentrations in asteroids and comets.
- Evidence of Impact: The discovery of this globally distributed iridium layer strongly supports the theory that a massive asteroid or comet impact caused the K-Pg extinction event. The high levels of iridium are believed to be fallout from the vaporized impactor that spread across the planet.
Properties of Iridium
Iridium is a dense, hard, silvery-white transition metal. Its unique properties make it valuable in various scientific and industrial applications, though its primary fame stems from its role in understanding Earth's past.
| Property | Value |
|---|---|
| Symbol | Ir |
| Atomic Number | 77 |
| Atomic Mass | 192.217 u |
| Density | 22.56 g/cm³ (one of the densest metals) |
| Melting Point | 2,466 °C (4,471 °F) |
| Group, Period | Group 9, Period 6 |
| Classification | Transition Metal |
The presence of this iridium anomaly serves as compelling evidence for the catastrophic extraterrestrial impact that reshaped life on Earth, leading to the demise of the dinosaurs and the rise of mammals.
For further information on the K-Pg boundary and the impact theory, you can explore resources from reputable scientific institutions like NASA's Earth Observatory: Cretaceous-Tertiary (K-T) Boundary.
