Have you ever asked why is there all around the world a thin ‘iridium layer’ inside shallow sedimentary layers? One would expect that this has to be from some meteorite hit, because meteorites often contain higher amounts of iridium.
The layers are exposed all over the world, but the thickest (richest) layers are found in the southern parts of the United States and Mexico. Scientists have been searching for a source of this layer for many years. Today, the prevailing idea is that it was caused by an asteroid that fell in the Yucatán Peninsula, at Chicxulub, Mexico 66 million years ago (Alvarez Hypothesis).
But… A careful person would ask first:
- There were many and many meteorite hits between 66 Ma – today, why don’t we observe similar ‘iridium layers’ from these sources?
- Wouldn’t that hit delivering an estimated energy of 10 billion Hiroshima A-bombs kill all living species (or at least all bigger species)?
If the iridium layer was the first one that you find in the shallow sedimentary sequence from above, you would try to find the youngest impact first. What about Meteor Crater in Arizona?
Here few dates:
- Est. age: 50,000 years
- Est. weight: 300,000 tonnes
- Type: Iron meteorite (IAB-MG)
- Biggest fragment weighing 1,409 lbs
- Ir-content: 1.9 ppm
- Crater diameter: 3,900 ft
66,000,000 vs 50,000 years is an extremely big gap, but have a look at the two mentioned questions again. Where is the 50,000 years old vaporized iridium-rich sedimentary layer from Canyon Diablo meteorite (Meteor Crater)?