How did they find the Chicxulub crater? They found the Chicxulub crater, the remains of the asteroid that wiped out the dinosaurs, when they were looking for oil.
The Chicxulub crater was made when an asteroid ten kilometers in diameter hit Earth. It landed just over 66 million years ago and left a crater that is 200 kilometers wide and 30 kilometers deep. The crater has an outer edge that reaches 300 kilometers. The actual age has been calculated at 66,043,000 years, plus or minus 11,000 years. The area where the asteroid hit is currently half on land and half at sea, but when it impacted, the whole area was under the sea. The asteroid was traveling at 20 kilometers per second. The impact caused winds of 1,000 km/h and tsunamis that might have reached 1.5 km in height. It ripped up the seabed and thrust hot ash, dust, and other materials into the atmosphere. Most of North and Central America would have been decimated by waves, earthquakes, and fires. The rest of the dinosaurs and a lot of other life were wiped out by the nuclear winter that followed.
The asteroid theory for the extinction of the dinosaurs is pretty widely accepted today, but it was only introduced in 1980. Two scientists, Luis Walter Alvarez and his son Walter, had discovered a layer of iridium-rich clay that appeared to circle the Earth. They found it in every place they looked and always at the same depth. Iridium is very rare on Earth, but it is very common on asteroids. The fact that there was a layer of iridium soil all over the Earth at the same depth implied that it had been put down at the same time and most likely by an asteroid impact that was large enough to spread it all over the world. The depth of the iridium corresponded to the Cretaceous-Tertiary extinction, and the Alvarez theory was born, but it was doubted by a lot of people. The only thing that could help prove it would be to find the crater, but that was unlikely. The majority of asteroids come down in the sea, which makes sense because 71% of the surface of Earth is sea.
Finding the impact site proved tricky. The Alvarez’s discovery sparked worldwide interest in the geology community, and they started hunting. An international conference, called Snowbird, was called in 1981 to coordinate all of the search efforts. Unbeknownst to all of these crater hunters, it had already been found. The Mexican state-owned oil company Petroleos Mexicanos had surveyed the area and even dug up core samples. The core samples had been dug up in the 1950s and stored. The survey had taken place in 1978, conducted by two geophysicists called Glen Penfield and Antonio Camargo. They were using magnetic data, and they found unusual readings which were consistent with an asteroid impact. Penfield took the results to his company, but they told him he couldn’t release them. Oil companies keep their geological data very secret, for fear of competition. Strangely, the oil company said he couldn’t release the data, but they did say he could present some of his results at the 1981 Society of Exploration Geophysicists conference. There were very few people at the conference to hear Penfield’s presentation about the impact crater because all of the experts were at the Snowbird conference talking about how they could find the impact crater. Penfield tried to contact Alvarez, but was unable. He had a story in a newspaper, but nobody saw it. Meanwhile, all of the geologists kept searching. They found shocked quartz, which is caused by an impact. They found weathered glass beads that were formed in the intense heat of an impact. Yet, they were looking in the wrong place. It was only in 1990, 12 years after Penfield found the crater and 10 years after Alvarez published his theory, that the people who knew where the crater was and the people who were looking for it came together. In this interconnected age of the Internet, that seems amazing. A group of geologists analyzed it, and they published their findings in 1990. They named the crater Chicxulub after a nearby town.
You might think you would be able to see the crater if you looked on Google Maps. That’s what I thought. You can’t see it, though, because millions of years of sediment and rock have completely covered it over. 66 million years is a lot of time for the land to change. The original land that was there when the asteroid landed is under at least a kilometer of new rock and soil. The land is slightly depressed, but not something you can see on Google Maps. There is also a ring of lakes called cenotes around the edge of the impact crater. The rock was fractured by the impact, and this lets water get in. The water dissolved the limestone and left caves and fissures that have been filled with water. And this is what I learned today.
Sources
https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html
https://en.wikipedia.org/wiki/Chicxulub_crater
https://www.lpi.usra.edu/science/kring/Chicxulub/discovery
https://www.ebsco.com/research-starters/geology/chicxulub-crater
Photo by Francesco Ungaro: https://www.pexels.com/photo/brown-mountain-crate-96457/