The Nadir Crater, which has a diameter of 5.3 miles (8.5 kilometers), was most likely created by an asteroid that collided with Earth 66 million years ago. The Nadir’s features are similar to the asteroid impact that caused the enormous extinction of the Cretaceous-Paleogene era. Both asteroids seem to have formed from the breakup of a parent asteroid or might have come from the same stream of asteroids.
66 million years ago, an asteroid of several tens of miles in diameter hit the Earth, causing the extinction of the non-avian dinosaurs—one of the most important extinctions in the history of the Earth. The event left an indelible mark, the Chicxulub crater, located not far from the Yucatán Peninsula in Mexico. Large asteroids (about 160 feet or 50 meters in diameter) collide with the Earth every 900 years; but larger asteroids (over 0.6 mi or 1 km in diameter) collide with the Earth once every million years.
To date, only a small proportion of hypervelocity impacts have been preserved or discovered. The impacts of large asteroids on the Earth are still poorly understood, despite the risk they represent. There are about 200 craters on Earth, of which only 15 to 20 are underwater impact craters—an astonishing number, considering that most of our planet is covered by water. But a new undersea crater may soon be added to the list.
The Nadir Crater has features consistent with an impact event
The Nadir Crater was discovered through the analysis of seismic data from the Guinean continental shelf of Africa. Instead of the flat sedimentary sequences expected on the shelf, the scientists found a depression of 5.2 mi (8.5 km) below the seafloor with very unusual features that had never been seen before.
The Nadir Crater is named Nadir after a nearby seamount and is buried beneath about 1000–1300 ft (300–400 m) of Paleogene sediments off West Africa, 250 mi (400 km) off the coast of Guinea. This depression displays features consistent with a large asteroid impact crater. These are a high rim above a stepped (or terraced) floor, a pronounced central uplift, and extensive subsurface deformation. Outside the crater, ejecta is discovered, as well as highly chaotic sedimentary deposits that extend for tens of miles around it.
There is little to no doubt that the Nadir Crater was formed by an asteroid. Other things that can cause craters to form, like the removal or dissolution of salt below the surface, the escape of gases or fluids, or the collapse of calderas, are indeed not compatible with these traits.
Numerical simulations of the Nadir Crater formation indicate that the asteroid that hit the area was at least 1,300 ft (400 m) in diameter and landed 1,600 to 2,600 ft (500 to 800 m) deep in the water. Depending on the type of land it hit and how close it was to people, an impactor the size of Nadir would kill 300,000 people today.
A series of disastrous events
The Nadir asteroid impact probably resulted in a gigantic tsunami, almost two miles high, as well as an earthquake of about magnitude 6.5. About 1,000 times more energy was released than in the eruption and tsunami in Tonga in January 2022.
The amount of volatiles and aerosols ejected into the atmosphere determines the climate consequences of such an event. According to the study, It is believed that the impact may have released substantial amounts of greenhouse gases, produced from the organic-rich black shale deposits buried at shallow depths.
The Nadir Crater formed at (or not far from) the Cretaceous-Paleogene boundary, about 66 million years ago; thus, the Nadir asteroid hit the Earth at about the same time as the Chicxulub asteroid, which together wiped out the non-avian dinosaurs. Because of the uncertainty in the resolution of the seismic data, the dating remains to be confirmed.
If this hypothesis proves to be true, the two dinosaur-killing asteroids are fragments of the same parent body, or a massive asteroid flow occurred at the time. The Nadir impactor is much smaller than the Chicxulub impactor, which forces scientists to investigate the possibility of a group of asteroid impacts that caused the extinction of the dinosaurs in the Late Cretaceous.