Drastic climate changes made Earth a difficult place for dinosaurs to survive.

Planet Earth would be a scary place for humans if dinosaurs still ruled the world. Though there are still some traces of life from the Jurassic period, like certain mollusks and types of reptiles, the Age of Dinosaurs ended more than 65 million years ago. Dinosaurs and many other creatures died off, never to return again. 

This mass extinction is believed to be the result of an asteroid hitting Earth. A new report by the journal Biological Reviews called ‘The Extinction of Dinosaurs” concludes that this impact was, indeed, the cause of the dinosaurs’ demise. But the space blast wasn’t the only reason these creatures aren’t still around today.

A Break in the Food Chain

Dinosaurs depended on each other to survive. Meat-eating monsters like the Tyrannosaurus Rex were at the top of the food chain, and fed off of plant eaters like the horned Triceratops. These herbivores were decreasing in population at the time of the asteroid, which left the carnivorous species less food to survive on. “In any ecosystem where you remove links to key species, that community has problems,” Richard Butler, one of the review’s authors, told National Geographic.

While the herbivore population was going down, Earth’s temperatures were rising. Years before the impact, the planet began experiencing a period of volcanism. These eruptions caused climate changes that affected both dinosaur and plant life, and further disrupted the food chain. Hot vapors and gas emitted by the volcanoes began wiping out some of the dinosaur population and weakening the survivors.

Deadly Climate Changes

These environmental factors made the asteroid’s impact especially powerful. It caused more volcanoes to erupt, heated up Earth's atmosphere, and led to a sharp drop in the level of oxygen in the oceans. For an already weak population, dinosaurs were helpless at the time of collision. “If the asteroid hit a few million years earlier, when dinosaurs were more diverse, or a few million years later, when they had a chance to recover as they often had done before after diversity losses, then dinosaurs probably wouldn’t have gone extinct,” said University of Edinburgh paleontologist and evolutionary biologist Stephen Brusatte, who led the study.

The ancient collision triggered more than a thousand years of destruction. With the dinosaurs gone, mammals began to evolve into bigger and more diverse species. Many animals we see today, like birds, sharks, and even some cats and dogs, emerged after the asteroid. But none rule the Earth quite like the dinosaurs did.