It has been a widely accepted theory that an asteroid caused the extinction of dinosaurs 66 million years ago.

But the question has always remained: how exactly did the asteroid wipe out most of life on earth?

Researchers at Tohoku University in Japan say they've found an explanation to why dinosaurs were wiped out, but other ancient animals lived on.

The theory, which was a joint study by the university and the Japan Meteorological Agency's Meteorological Research Institute, concluded that aerosol-soot in the air caused by the asteroid led to major climate changes which in turn led to the mass extinction of life 66 million years ago.


The team, led by Tohoku University Professor Kunio Kaiho, conducted the study by examining earth samples from Haiti and Spain - somewhere close to the crater of the asteroid, also known as the Chicxulub impactor, and somewhere far.

They discovered that both samples of the sedimentary organic molecules contained "combusted organic molecules showing high energy".

This is what they believed to be the soot.

The researchers then calculated the amount of soot in the stratosphere to estimate the global climate changes caused by the "strong, light absorbing aerosol".

Earlier scientific theories proposed that dust from the asteroid impact had blocked the sun and caused the mass extinction.

But Prof Kaiho's team disagree, having said it's unlikely the dust could have lingered in the air long enough to cause extinction.

"If this had occurred, crocodilians and various other animals would have also gone extinct," Prof Kaiho's team said.

According to the new hypothesis, when the asteroid struck the oil-rich area of Chicxulub in the Yucatán Peninsula, Mexico, a significant amount of soot was released and spread globally, causing a long period of darkness.

This then caused "colder climates at mid-high latitudes, and drought with milder cooling at low latitudes on land ... 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", Kaiho's team reported.

The rapid pace of these climate changes are what the researchers are saying explains the extinction of dinosaurs but the survival of 90 per cent of the ocean life in the Cretaceous period.

Prof Kaiho's team also explained that other creatures may have survived the aftermath of the asteroid by hiding themselves underground.

And as for sea creatures - there was a significant change to the temperature of the surface of the water, but deep down, there was very little change so most underwater animals survived.