The Day Life on Earth Almost Died

A Piece of the KT Boundary

Around the end of July, I wrote a post entitled Revisiting the Cretaceous Extinction. This week, I read a fascinating story entitled “The Day the Earth Died” in the April 8, 2019 issue of The New Yorker. The asteroid that collided with Earth around 65 million years ago was at least six miles wide and gouged a crater about eighteen miles deep and launched 25 trillion metric tons of debris into the atmosphere. The article goes on:

The damage had only begun. Scientists still debate many of the details, which are derived from the computer models, and from field studies of the debris layer, knowledge of extinction rates, fossils and microfossils, and many other clues. But the over-all view is consistently grim. The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. Photosynthesis all but stopped, killing most of the plant life, extinguishing the phyto-plankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. After the fires died down, Earth plunged into a period of cold, perhaps even a deep freeze. Earth’s two essential food chains, in the sea and on land, collapsed. About seventy-five per cent of all species went extinct. More than 99.9999% of all living organisms on Earth died, and the carbon cycle came to a halt.

This massive disaster left a signature layer across the entire surface of the planet referred to as the KT boundary, short for Cretaceous-Tertiary. (It is also referred to as the KPg boundary after the Tertiary was renamed the Paleogene by geologists.) This boundary layer is high in the rare element Iridium, which is most often found in meteorites and asteroids.

It is a sobering thought that an object from space only six miles across (10 km) could strike the Earth, which is eight thousand miles across (12,900 km) and end up killing virtually all life, and certainly annihilating the human race.

The asteroid collided with the Earth around Chicxulub on the Yucatán peninsula, which I plan to visit, hopefully with a geologist, early next year.

Revisiting the Cretaceous Extinction

This Yucatán Fishing Village Along the Gulf of Mexico Hides a Secret

A few miles from Progreso, Yucatán, is the fishing village of Chicxulub (CHEEK-shoe-lube) which was the site of one of the great catastrophes in the life of the earth. Some 65 million years ago, an asteroid that was nine miles (fifteen kilometers) across slammed into Chicxulub at the speed of 44,640 mph (or 20 km/second) and destroyed some three quarters of all the life on earth, including all the dinosaurs. The impact was equivalent to a million times larger than the largest hydrogen bomb explosion and created a crater that was sixty miles (100 km) across and eighteen miles (30 km) deep.

Of course, that was millions of years ago, and the geology of the area has changed significantly.

Where the Asteroid Impacted


Signs of the Impact Today: A Ring of Cenotes

Today, the Yucatán Peninsula is a large limestone chunk that has been raised up, but with numerous underground rivers and caves admitting access to the water beneath. What you will not find there a river. This did not make it easy for the ancient Maya to grow crops—except in their areas where cenotes prevail. The dark green aresa beneath the ring of cenotes is where the Puuc Hills are located, which rise to an elevation of several hundred feet. There, the Maya dug cisterns, called chultunes, which frequently run dry during periods of drought.

I hope to visit Chicxulub Puerto when I stay in Merida or Progreso.