The exact reason behind the
extinction of dinosaurs is still a topic of continuous debate and discussion. There have been varying opinions regarding the topic and what has caught the attention recently is that an asteroid impact ended the reign of the dinosaurs 65 million years ago. A new study conducted by an international team of 41 researchers strengthens the claim further. The finding has been published in the journal science.
According to the study, the
fossil record clearly shows a mass extinction event that has happened across the planet around 65 million years ago. During the course of that incident around 70% of known species have suddenly vanished. The change was so dramatic and the geologists have used it to define the boundaries as the end of the Cretaceous and the start of the Palaeogene periods, otherwise the K-T boundary event.
It has been known that the idea that an asteroid was responsible for the end of the age of the dinosaurs was first proposed 30 years. Scientists discovered large amounts of element iridium which is rare on earth but abundantly found in asteroids and meteorites. This has been considered as the first clue substantiating the studies of the impact. The elements have been appearing in a layer across the globe at the time of the K-T boundary event.
The
asteroid impact theory was further supported in 1991 with the discovery of a 200-kilometre wide impact crater at Chicxulub on Mexico's Yucatan Peninsula. This provided what many scientists believe is the 'smoking gun' substantiating the theory. However some scientists challenge this hypothesis pointing out that deposit of tiny glass like blobs of melted impact material have been seen around Chicxulub. This predates the extinction event by 300,000 years. According to them, the mass extinction has been caused by the Deccan Traps, unusually active volcanoes in what is now India, led to global cooling and acid rain.
The researchers have examined the sedimentary material around the impact site and found it was far too violently churned up to provide a reliable dating record in the latest study. The studies also reveal that further away from the impact site, the sedimentary material becomes a single layer at the K-T boundary. This matches the composition of rocks at Chicxulub. They have also figured out that even though there has been evidence for relatively active volcanism in India, the ecosystems revealed only minor changes within the 500,000 years before the K-T boundary event. The point to be noted is that only at the boundary do things suddenly change.
There are also similar theories that strongly counter the Deccan hypothesis. They say that the atmospheric chemistry models show that while significant volumes of sulphur were emitted during each volcanic eruption forming aerosols in the stratosphere. They would be dropped rapidly with only short-lasting environmental effects. According to the researchers the Chicxulub impact saw much larger volumes of sulphur, dust and soot released in a much shorter time frame. This has led to extreme environmental changes such as darkening and cooling.
