A new hypothesis on the extinction of
dinosaurs and ammonites at the end of the Cretaceous Period has been
proposed by a research team from Tohoku University and the Japan
Meteorological Agency’s Meteorological Research Institute.
The researchers 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, they say, could have been the process that led to the
mass extinction of dinosaurs and ammonites.
The asteroid, also known as the Chicxulub impactor, hit Earth some 66
million years ago, causing a crater more than 180 km wide. It’s long
been believed that that event triggered the mass extinction that led to
the macroevolution of mammals and the appearance of humans.
Tohoku University Professor Kunio Kaiho and his team analyzed
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 from the asteroid
crash.
Soot is a strong, light-absorbing aerosol, and Kaiho’s team 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 developed at the Meteorological
Research Institute. 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. In other words, they’d figured out the
killer, but not the murder weapon.
Earlier theories had suggested that dust from the impact may have
blocked the sun, or that sulphates may have contaminated the atmosphere.
But researchers say it is unlikely that either phenomenon could have
lasted long enough to have driven the extinction.
The new hypothesis raised by Kaiho’s team says 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 their 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 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.
Kaiho’s team is studying other mass extinctions in the hopes of further understanding the processes behind them.
