Mass Extinction Monday | END-CRETACEOUS (65 Ma)

[Also formerly known as the Cretaceous-Tertiary (K-T) and now as the Cretaceous-Paleogene (K-Pg) extinction]

Severity: 5th worst

Cause: Meteorite impact released CO₂ from carbonates

Climate: Cold (SO₂) then warm (CO₂)

Aftermath: Mammals arise

Even though the End-Cretaceous is the least severe of all the mass extinctions, with 62% of species and 11% of families wiped out, it’s probably the most well-known. (Say goodbye to our dinosaur friends!) The hardest hit animals included: dinosaurs (except Aves), pterosaurs, corals, echinoids, ammonites and belemnites, brachiopods, bivalve molluscs, and foraminifera.

Luckily for us, mammals were among those that fared better, along with turtles, lizards and snakes, birds, amphibians, and fish.

Most people are familiar with the theory that a meteorite impact was the cause of this mass extinction, but what really did happen and what can be proven?

Back in 1980 in Gubbio, Italy, father-son duo of Luis and Walter Alvarez measured an iridium abundance in the K-Pg boundary clay. Iridium is not a very common element in the Earth’s crust, so they knew it must have come from an extraterrestrial source. This observation would lead to inferring that there must have been a massive meteorite impact, but they would have to find the actual impact crater.

In the K-Pg boundary layer around the Caribbean, tektites, shocked quartz, and tsunami deposits were discovered, all of which would be indicative of a nearby meteorite impact.

The half-submerged Chicxulub crater was soon discovered in the Yucatan of Mexico, and impact glass yielded a ³⁹Ar/⁴⁰Ar age of 65 Ma, the exact age of the K-Pg boundary, making it the perfect candidate.

A large portion of this impact’s deadliness would have been due to the target rocks, which are mainly carbonates and evaporites. Upon impact, the rocks would have been vaporized, releasing large amounts of CO₂ and SO₂.

However, this mystery still isn’t fully solved. Around the same time, the Deccan Traps in India were effusively erupting, and as we saw in the End-Permain extinction, flood basalt events can produce absolutely disastrous effects.

We then have to ask ourselves: Was the impact really the only (or primary) cause of the extinction? What would have been the actual kill mechanism? And what was the role of the Deccan Traps?

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