Possible Explanations for the K-T Extinction

Asteroid Theory


The asteroid theory is based on the finding of Luis Alvarez, a physicist, and his son, Walter Alvarez, a geologist. In 1980, they discovered that sedimentary layers found at K-T Boundary contain a concentration of iridium many times greater than normal. Iridium is extremely rare in the earth's crust because it is a "siderophile element" ("iron-loving"), meaning that most of it travelled with the iron as it sunk into the earth's core. As the element remains in high quantities in most asteroids and comets, the Alvarez team suggested that an asteroid had struck the earth at the time of the K-T Boundary. This was the first evidence uncovered that supported the asteroid theory. 


An impact of this magnitude would have caused a massive amount of dust and debris creating a dust cloud, which would have blocked the sun for 6 to 12 months and inhibited photosynthesis. The impact also would have sent sulfuric acid aerosols into the stratosphere, which would have reduced the sunlight reaching the Earth's surface by 10-20%. It would have taken up to ten years for those aerosols to dissipate.


This hypothesis was disputed and even disregarded by many scientists and paleontologists for many years. However, today most scientists have accepted the theory and have even established where the asteroid may have impacted: Chicxulub, Mexico. The crater is not visible on land, but powerful photographs taken in space clearly show the crater. 





However, in 2004 scientists who were doing research on the crater said that a core drilled out of the middle of the crater dated back to more than 300,000 years before the K-T Boundary, and therefore could not have caused the mass extinction.


There are other craters around the world which scientists believe may have contributed to the extinction. This theory is known as a multiple-impact event. These craters are:

• Boltysh crater, Ukraine
• Shiva crater, Indian Ocean
• Silverpit crater, North Sea
• Eagle Butte crater, Canada
• Vista Alegre crater, Brazil