How did asteroid impact wipe out dinosaurs?

Tokyo, July 17 (IANS) While it is widely accepted that an asteroid impact caused the mass extinction of dinosaurs and other life forms, researchers have been stumped by the process of how. In other words, they had figured out the killer, but not the murder weapon.

A new study has now said that when the asteroid hit the oil-rich region of Yucatan Peninsula in Mexico, a massive amount of soot was ejected which then spread globally, causing global cooling, drought and limited cessation of photosynthesis in oceans.

This could have been the process that led to the mass extinction of dinosaurs, said the research team from Tohoku University and the Japan Meteorological Agency's Research Institute.

The asteroid, also known as the Chicxulub impactor, hit Earth some 66 million years ago, causing a crater more than 180 km wide.

Professor Kunio Kaiho from Tohoku University and his team analysed sedimentary organic molecules from two places -- Haiti, which is near the impact site, and Spain, which is far.

They found that the impact layer of both areas have the same composition of combusted organic molecules showing high energy.

This, they believe, is the soot -- a strong, light-absorbing aerosol -- from the asteroid crash.

The results were significant because they could explain the pattern of extinction and survival.

Earlier theories had suggested that dust from the impact may have blocked the sun, or that sulphates may have contaminated the atmosphere.

But it was unlikely that either phenomenon could have lasted long enough to have driven the extinction, the researchers noted.

According to their study, when the asteroid hit the region, the massive amount of soot had caused a prolonged period of darkness which led to a drop in atmospheric temperature.

The soot aerosols caused colder climates at mid-high latitudes, and drought with milder cooling at low latitudes on land.

This in turn led to the cessation of photosynthesis in oceans in the first two years, followed by surface-water cooling in oceans in subsequent years.

This rapid climate change is believed to be behind the loss of land and marine creatures over several years, suggesting that rapid global climate change can and did play a major role in driving extinction.

The study was published in the journal Scientific Reports.