Dinosaurs are a diverse group of reptiles of the species Dinosauria. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research, they are believed to have first appeared in between 243 and 233.23 million years ago. They became the dominant vertebrates throughout the Jurassic and Cretaceous periods. Dinosaurs roamed around the earth for 160 million years until their ultimate demise some 65.5 million years ago, in an event now called as the Cretaceous-Tertiary, or K-T, extinction event. Besides dinosaurs, many other species of plants, mammals, and amphibians were also wiped out.
Over the years, paleontologists have proposed several theories on the extinction of dinosaurs. One early theory states dinosaurs having a breeding problem. In another theory, scientists believed a great plague decreased the dinosaur population and then spread to the animals that feasted on their carcasses causing them to die-off. Starvation was also another possibility as they are known to have a huge appetite. There was also a volcanic eruption event that matches with the timeline of their extinction.
In the 1980s, physicist Luis Alvarez and his geologist son discovered a distinct layer of iridium–a rare element found in abundance only in space–that corresponds to the precise time the dinosaurs died in Italy. Iridium is a rarely found in Earth’s crust but is more abundant in stony meteorites, which led the Alvarez duo to conclude that the mass extinction may have caused when an extraterrestrial object collided with earth. This impact hypothesis is also known as the Alvarez hypothesis. This theory suggests that a comet, asteroid or meteor that fall on earth surface may have caused the extinction of the dinosaurs. The asteroid hit at high velocity creating a huge crater. The instantaneous devastation in the immediate vicinity and the widespread aftermath of an asteroid threw vast amounts of material up into the atmosphere filling it with gas, dust, and debris that drastically altered the climate. It soon went travelling all around the world affecting the whole ecosystem. Like dominos, this affected the food chain, causing the ecosystem to collapse. The reduction in plant life created a huge impact on herbivores’ ability to survive, which eventually lead carnivores to suffer from food scarcity. All living organism would have been affected in some way, both on land and in the ocean. The casualty list is long. Among them, reptiles, ammonites, some microscopic plankton, and large marine life were also wiped.
The Alvarez hypothesis was initially highly controversial. Eventually, other scientists began finding pieces of evidence of iridium at various places around the globe that supported the Alvarez theory. In the early 1990s, another impact site, known as the ,Chicxulub crater, centered on the Yucatán Peninsula in Mexico was discovered. The asteroid is thought to have been between 10 and 15 kilometers wide, and the velocity of its collision caused the creation of 150 kilometers in diameter of the crater- the second-largest crater found on the planet. This discovery further provided strong evidence that their extinction was caused by the asteroid.
The blame can’t solely put on the asteroid though. Prior to the asteroid collision, Earth was already experiencing climate change. This was making things living harder on the planet. In what is now India, there was a substantial volcanic activity that causing problems of its own. For two million years, volcanic activity was spewing gases into the atmosphere and having a major impact on global climate. There were also ongoing longer-term changes. The continents were drifting around and splitting apart from each other, creating bigger oceans. This also caused a strong impact on climate and vegetation.
All of the non-bird dinosaurs died out, but flying dinosaurs did survive. Initially, the survivors were small, there were a couple of lineages of gigantic birds – predatory and herbivorous – but they weren’t unable to survive for long and also went extinct but the lineages that led to modern birds survived. Dinosaurs still remain the largest land animals ever to have lived. Their extinction marked the end of the Cretaceous period, and with it ended the entire Mesozoic, Era, marking the beginning of Cenozoic Era that continues to today.
The debate may rage for many years, as scientists explore and dig up new pieces of evidence or develop new tools, techniques to better understand the past. But whether space invaders or loads of lava are to blame, it’s clear that studies of dinosaurs’ extinction is revealing vital information about the effects of dramatic climate change on Earth’s inhabitants. This leads to the question what our ending will look like. What’s there to come for the future? What will be our fate?