The day the Dinosaurs Died

August 11, 2016

Just finished a fascinating chapter in The Sixth Extinction titled The Luck of the Ammonites, or un-luck as fate would have it. We’ve all heard that the dinosaurs were exterminated by a massive asteroid hitting the Earth and causing Nuclear Winter. However that’s pretty much all I knew. This chapter narrates the rest of the story. Very Interesting!

Back in 1969, Walter Alvarez was fascinated by a thin layer of sediment (dubbed the K-T Layer because it separates the Cretaceous and Paleogene periods) just outside of Gubbio Italy. He was intrigued because of the huge differences in fossils between the layers immediately above and below this area. Later, back in California, he sparked an interest of this anomaly in his father, Luis – a professor at Berkley.

In one of their experiments, they tested the clay samples for iridium, a rare,on Earth, element but abundant on asteroids. The iridium levels were off the charts. They did not know what to make of this anomaly. However, they were able to obtain and test clay samples of the same layers from other parts of the World all with the same results. All had the same extremely high iridium levels.

They tried out numerous theories before settling on the Impact Hypothesis in 1980:

65 million years ago an asteroid 6 miles in diameter crashed into the Earth with an impact of more than a 100 million hydrogen bombs. Debris including iridium from the asteroid spread around the globe causing Nuclear Winter (A Carl Sagan addition) thus resulting in the extinction of 75% of the life on Earth.

The Alvarez’s were labeled charlatans after publishing their theory by the entire scientific community. The prevailing theory was Darwin’s Natural Selection wherein species evolved or became extinct gradually over millions of years.

Thus began the search to find the “smoking gun” – the asteroid crater. The general criteria were 65 million years old and maybe a couple of hundred miles in diameter. No know crater fit the criteria. Finally, on the banks of Texas’ Brazos River scientist came across patterns consistent with a “nearby impact” thereby narrowing the search to the Gulf of Mexico area. Finally, the missing piece, a 100 mile wide crater was located just off the Yucatan Peninsula with the help of drilling samples taken years earlier by PEMEX.

Not only the dinosaurs but over 75% of life on Earth at that time was eliminated. Not only on the surface, but in the air, and in the sea also. Not only animals but plants were not spared execution either. The striking difference in the fossils above and below the K-T layer provide the Great Extinction’s evidence.

If your interested, I recommend The Sixth Extension book. There are also some good resources on the web including:

Almost forgot, Ammonites were a sea creature that became extinct during the K-T Event. Their fossils were numerous in the Gubbio layer.


  1. For movie fans the Cretaceous Period follows the Jurassic Period.
  2. How do you get K-T from Cretaceous–Paleogene? Cretaceous is usually abbreviated K for its German translation Kreide (chalk) derived from the Latin “creta” (chalk). The Paleogene Period was created bu splitting the Tertiary Period into two periods: Paleogene and Neogene.