The Cretaceous–Paleogene (K-Pg) extinction event occurred approximately 66 million years ago, marking the end of the dinosaurs and many other species. This catastrophic extinction was caused by the impact of a large celestial body into what is now the Yucatán Peninsula in Mexico. The resulting Chicxulub crater serves as a geological record, prompting scientists to reconstruct the exact physics of the collision. Determining the speed and force of this impactor requires a combination of geology, physics, and computational modeling to establish the quantitative details of this mass extinction.
Determining the Impact Velocity
The speed of the Chicxulub impactor is estimated to have been between 15 and 22 kilometers per second when it struck Earth’s surface. This velocity range is roughly equivalent to 33,500 to 49,200 miles per hour. The minimum possible speed for any object to strike Earth is 11 kilometers per second, which is the planet’s escape velocity, meaning the Chicxulub object was traveling significantly faster than the bare minimum.
Scientists calculate this speed by analyzing the physical characteristics of the resulting crater, which spans approximately 200 kilometers in diameter. Computer hydrocode models simulate impacts at various speeds and angles, comparing the simulated dimensions and rock deformation to the actual structure of the Chicxulub crater. These models suggest the object arrived at a steep angle, estimated to be between 45 and 60 degrees from the horizontal, impacting from the northeast.
The depth and shape of the transient crater, the temporary cavity formed milliseconds after impact, are direct functions of the impactor’s velocity, mass, and angle. Researchers refine the velocity estimate by working backward from the geological evidence, with many modern analyses settling on a figure near 20 kilometers per second. This determination relies on gravitational acceleration, which increases the speed of the incoming space rock as it falls toward Earth.
The Size and Mass of the Chicxulub Impactor
The physical dimensions of the object were necessary inputs to understand the scale of the destruction. The Chicxulub impactor is estimated to have been an asteroid with a diameter of approximately 10 to 15 kilometers. If this object were placed on Earth’s surface, its height would have exceeded that of Mount Everest.
Based on the calculated size and composition, the object’s mass is estimated to have been around 1.0 x 10^15 kilograms. Evidence suggests the impactor was a C-type asteroid, meaning it had a carbonaceous chondrite composition. This type of asteroid is relatively dark and volatile-rich, originating from the outer regions of the main asteroid belt.
The object’s mass combined with its high velocity determined the total kinetic energy it carried. Kinetic energy is proportional to the object’s mass multiplied by the square of its velocity. Therefore, both the physical size and the speed were significant factors in the destructive power unleashed upon impact. The composition is also important because it influences the amount of climatically active gases released from the vaporized rock.
Energy Release and Immediate Global Effects
The impact converted the asteroid’s massive kinetic energy into a destructive force estimated to be the equivalent of 72 teratonnes of TNT. This energy release is roughly comparable to 100 million megatons of conventional explosives. The immediate consequence was the creation of a superheated plasma core that reached temperatures exceeding 10,000 degrees Celsius.
A seismic shockwave radiated outward, causing ground shaking equivalent to a magnitude 10 or 11 earthquake. Simultaneously, an atmospheric shockwave, or airblast, devastated the surrounding region, generating winds that surpassed 1,000 kilometers per hour near the blast center. This airblast scoured the land and shredded vegetation in a radius extending up to 1,800 kilometers from the point of impact.
The impact also ejected molten rock and superheated debris, known as tektites, high above the atmosphere. As these glowing fragments re-entered the atmosphere across the globe, they created a worldwide thermal pulse that ignited widespread firestorms. Since the impact occurred partially in a shallow sea, the strike generated colossal tsunamis that radiated across the Gulf of Mexico and into the Atlantic basin. These waves are estimated to have reached heights of 50 to 300 meters as they crashed onto nearby coastlines.