Around 66 million years ago, dinosaurs ruled the earth. They were the most dominant of land animals and the most ferocious too. Until that time, they had lived on earth for 165 million years! Compare that with the rise of the homo sapiens- we have been on earth for only about 2 million years- and 165 million years seems such a long, long time. Which brings us to the question- why did a species that dominated earth so absolutely and for so long become extinct all of a sudden?
Ever since the first dinosaur fossils were discovered, dinosaurs have captured our collective imaginations. And this question continues to confound scientists, palaeontologists, and others of their ilk. The cause of the mass extinction that marked the end of the Cretaceous period is a scientific mystery. Even more confounding is the question as to why some species survived what must have been a major catastrophe on earth, while dinosaurs were wiped out.
Scientists can only guesstimate the answers. No one knows for sure the reason for the dinosaurs going extinct. Recent discoveries have however brought us closer to the answers, or so we presume. Two theories seem to be the most plausible reasons for the end of the age of dinosaurs- an extra-terrestrial impact, by an asteroid or comet, or a massive spell of volcanism.
Either scenario would have choked the skies with gases, debris etc. blotting out the sunlight for months or maybe years, thus spelling an end to photosynthesis. Green plants may have shrivelled up, leading to a cascading effect up the food chain, with the herbivores dying out first and then the carnivores, i.e. the dinosaurs dying en masse. Any life that survived would have been snuffed out by the soaring levels of greenhouse gases and subsequent climate change towards extreme climate conditions.
The asteroid theory gains momentum due to the discovery of a layer of iridium-rich rock dating precisely to around 65 million years ago. This layer is widespread across the world, both on land and in the oceans. While Iridium is uncommon on Earth, it is found in meteorites and also in the same ratio as in this iridium-rich layer of rock. Thus, scientists speculated that a huge asteroid struck the earth sixty five million years ago, scattering its iridium across the world and killing the dinosaurs on impact.
Another interesting discovery added fuel to this already raging theory. A 180 kilometre wide crater called Chicxulub has been discovered in Mexico’s Yucatán Peninsula, and which has been dated to 65 million years ago. The discovery of this crater lends credibility to the asteroid theory, which many scientists believe must have impacted earth and released 10 billion times the energy as the nuclear bomb dropped on Hiroshima, Japan, in 1945. What followed was huge tsunamis, raging fires, a thick blanket of dust and debris over the earth blotting out the sunlight, unrelenting darkness, finally ending with the extinction of one in three species of plants and animals, including dinosaurs.
Besides celestial objects, the other place iridium is found in abundance is in the core of the earth. This led to the rise of the theory that around sixty five million years ago, the earth spewed out massive amounts of magma in flood-like flows in ancient India. This magma flow piled up more than 2.4 kilometres thick over an area of 2.6 million square kilometres of Deccan India. The massive nature of the volcanic eruption would have spread the iridium around the world, and given rise to colossal amounts of sunlight-blocking dust and debris, along with loads of greenhouse gases.
Either scenario would have resulted in a massive dying out of life forms on earth. While both theories have their merits and demerits, the question that confounds is how did some of the species survive this catastrophe, and go on to prosper in later periods- the mammals, for example.
The actual facts will remain hidden until new discoveries shed further light on the greatest mystery of the Earth’s history- what really happened to the dinosaurs!