K-T iridium layer, Raton NM

The first concrete evidence that an asteroid impact ended the Cretaceous Period was the discovery of an iridium-rich layer marking the Cretaceous-Tertiary (K-T) boundary by a team led by Luis Alvarez in the early 1980s. Iridium is very rare in Earth’s crust, but is considerably more abundant in asteroids, leading geologists to conclude that the layer originated from an asteroid impact. One area where this layer is exposed is in several places near Raton, New Mexico. After our trip to Great Sand Dunes National park last week, we took a little side trip so I could see the K-T iridium layer, conveniently marked by a sign west of Raton.

Me with my fingers on the K-T iridium layer
Me with my fingers on the K-T iridium layer

Google map showing the location of the iridium layer exposure:

Grace and Peace

4 thoughts on “K-T iridium layer, Raton NM

  1. riverdok

    Earth has theoretically received multiple asteroid impacts.
    Why are there not multiple iridium layers, even on a local basis, adjacent to impact craters around the world, and at different depths according to the era of impact?


  2. Tim Helble

    Just looking at what geologists refer to as the Phanerozoic Eon (542 MY to present), not everywhere on the planet has layers from every epoch in that eon (e.g., Cambrian, Ordovician, etc.) because erosion has completely removed many layers. If an iridium layer existed in a formation that has long since been eroded away at a given location, you obviously wouldn’t be able to find it there.


  3. riverdok

    Thanks for the insight…on the same thread, is there evidence of erosion having obliterated any significant areas of the K-T iridium layer anywhere on the planet?


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