HARBIN - New findings suggest that a prehistoric asteroid collision is not solely responsible for wiping out the dinosaur population in northeast Asia 65 million years ago.

Scientists now claim that the end of the long-gone reptile's reign in some regions of northeast Asia can be linked to several other factors, including volcanic eruption, climate change and drops in sea level.

A new China-led study by 30 scientists from eight different countries has yielded powerful evidence challenging the dominant, decades-old scientific theory that dinosaurs were wiped out after an asteroid collided with the earth.

The study was made public during an ongoing seminar of geology and paleontology in Jiayin, a county in northeastern Heilongjiang province, where scientists have found fossils of dinosaurs living just before the species' sudden demise.

The scientists, including experts from Russia, the US, Germany, Belgium, Britain, Japan and the Republic of Korea, were led by Sun Ge of Jilin University in northeast China. Together, they have spent the past ten years studying the extinction of dinosaurs.

The study showed that in Jiayin the K-T boundary, the geologic boundary between the rocks of the Cretaceous and Tertiary periods, does not contain high-levels of iridium, a radioactive element that linked an asteroid strike to the extinction of dinosaurs.

The asteroid theory has dominated dinosaur studies for several decades after scientists found high-levels of iridium in the K-T boundaries in North America and other regions. The element is rare on Earth, but found in extraterrestrial objects, including asteroids, according to Sun Ge.

Among conflicting and controversial hypotheses explaining dinosaur extinction, the asteroid theory is the only one that has been proven by scientific evidence and is universally recognized by scientists, Sun said.

Scientists believe a giant asteroid that hit the earth about 65 million years ago sealed the fate of dinosaurs forever by throwing up gusts of dust or chemical clouds that blocked sunlight from reaching the planet, or by igniting global wildfires.

However, the new study suggests that volcanic activities around that time greatly impacted the environment of the Jiayin area and could be to blame for the species' extinction.

Geologic features of and around the K-T boundary in Jiayin are identical to those of and around the same layer in Russian regions of Siberia and the Far East, said Sun Ge.

Regions in northeast Asia had similar geographic environments 65 million years ago, where volcanic eruption, climate cooling and up to 100-meter drops in sea-level might have been the major factors that wiped out the dinosaurs, said Akhmetiev M, a Russian geologist who participated in the program.

According to Sun, the world's 105 sections of K-T boundary suggest a mega-wipeout 65 million years ago that destroyed over 70 percent of all the earth's species, including the dinosaurs.

The extinction of dinosaurs was caused by different factors in different regions, and an asteroid is not the only reason, Sun said.