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.