Adriana C. Ocampo: 1955—: Planetary Geologist

The theory that a large asteroid crashed into Earth, starting a chain of events that led to mass extinctions, was first proposed by the physicist Luis Alvarez, his son—geologist Walter Alvarez, and others in the early 1980s. The only evidence at the time was the existence of a thin layer of the rare element iridium in 65-million-year-old geological strata called the K/T boundary because it demarcates the geological shift from the Cretaceous to the Tertiary periods. Iridium is more prevalent in comets and asteroids than on Earth. The scientists postulated that the impact led to global fires, smoke, and dust clouds that blocked the sun, cooling the planet and preventing photosynthesis.

In 1981 oil geologists discovered the buried Chicxulub crater on the coast of Yucatán, estimated to be about 120 miles (200 kilometers) in diameter. In 1989 and 1990 Ocampo, her then-husband Dr. Kevin O. Pope, and Charles Duller were using satellite images to map water resources in the Yucatán. They found a semicircular ring of sinkholes, called "cenotes," that Ocampo recognized as related to the crater. They hypothesized that the crater might be the K/T impact site and published their findings in the journal Nature in May of 1991.

Ocampo joined the Chicxulub Consortium, a joint venture by American and Mexican scientists, to study the crater. In 1991 Ocampo and Pope led an international expedition of scientists and volunteers, sponsored by the Exobiology Program of NASA's Office of Space Science and The Planetary Society (TPS) of Pasadena. The expedition discovered two new sites. The site in Alvaro Obregon, Mexico, consists of two layers of material, called ejecta, that were thrown out by the impact and flowed lava-like across the surface in fluidized ejecta lobes. Impact ejecta are very rare on Earth and these were the first such lobes to be observed directly. The surface exposure of ejecta at Alvaro Obregon is the closest to the Chicxulub crater that has been found and is the best example known from a big impact crater.

The discovery of the Chicxulub ejecta lobes has important implications for understanding Mars. Ejecta lobes cover much of Mars, since its surface has remained unchanged for billions of years, preserving the debris from rare impacts. Ocampo told the JPL newsletter "Stardust:" "The discovery of these new ejecta sites is very exciting. It is like seeing a bit of Mars on Earth."