Soot from rocks after asteroid impact may have wiped out dinosaurs

Massive amounts of soot ejected from rocks following an asteroid impact caused global cooling and drought that may have led to the mass extinction of dinosaurs 66 million years ago, a new study suggests.

Researchers from the Tohoku University and the Meteorological Research Institute in Japan believe that massive amounts of stratospheric soot ejected from rocks following the famous Chicxulub asteroid impact, caused global cooling, drought and limited cessation of photosynthesis in oceans. This may have led to the mass extinction of dinosaurs and ammonites at the end of the Cretaceous Period, they said.

The asteroid, also known as the Chicxulub impactor, caused a crater more than 180 km wide. It had long been believed that the event triggered the mass extinction that led to the macroevolution of mammals and the appearance of humans.

Researchers 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 is the soot from the asteroid crash, they have said.

Soot is a strong, light-absorbing aerosol. Researchers came by their hypothesis by calculating the amount of soot in the stratosphere estimating global climate changes caused by the stratospheric soot aerosols using a global climate model. The results are significant because they can explain the pattern of extinction and survival.

While it is widely accepted that the Chicxulub impact caused the mass extinction of dinosaurs and other life forms, researchers have been stumped by the process of how.

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

However, researchers said it is unlikely that either phenomenon could have lasted long enough to have driven the extinction. The new hypothesis states that soot from hydrocarbons had caused a prolonged period of darkness which led to a drop in atmospheric temperature.

The team found direct evidence of hydrocarbon soot in the impact layers and created models showing how this soot would have affected the climate.

According to the study, when the asteroid hit the oil-rich region of Chicxulub, a massive amount of soot was ejected which then spread globally.

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