By Stephen Monahan

Discovered by Luis and his son Walter Alvarez in 1980 Proposed Asteroid Theory

Lack of evidence of other opposing theories, made volcanic theory the given cause Correlates to knowledge about other mass extinctions

A piece of limestone From "great dying“ Neutron activation analysis (NAA) by Asaro and Michel Allowed for precise measurements Discovered twenty-five time increase of iridium

Unlikely that so many species killed in short period of time Single event of the asteroid hitting the earth or a succession of events caused the extinction Time is often evidence to the contrary

Gerta Keller studies of many rock formations Fossil remains to date surrounding geologic features El Penon, 52 species discovered in the layer below asteroid layer found in layer above Concluded that volcanoes was more likely

In 1991, scientists found a impact crater New data from debris suggest extinction and impact happened within 33,000 years period A small layer of sediment around the world contains a lot of iridium Collection of 45 scientists from different fields Went through each possible cause

The impact from the asteroid made subsurface rocks unstable by disturbing them Dust sent into the atmosphere from the impact Significant variations in the climate Global wildfires Modern View is not unanimous but mostly to Asteroid Theory