Why are dinisores in extinct?

Dinosaurs were not all wiped out by an asteroid impact 66 million years ago—some researchers believe that a select group of small, feathered dinosaurs survived and grew into modern birds. But the asteroid collision did cause the extinction of all other land-based dinosaurs, likely by blocking sunlight and lowering global temperatures by as much as 26 degrees Celsius.

Many other theories—including disease, shifts in continental position and volcanoes—have been proposed to explain why dinosaurs went extinct, but the idea of an asteroid impact remains the most popular. The impact would have caused wildfires, tsunamis and a prolonged dust cloud that blocked out sunlight and made photosynthesis impossible. Almost 75 percent of all animal and plant species were wiped out, including all of the dinosaurs except the birds.

One of the reasons that the asteroid collision theory is so convincing is that there’s actual physical evidence to back it up. When an asteroid or comet of around six miles across struck what’s now the Yucatán Peninsula in Mexico, the force of the collision hurled pulverized rock and debris into the atmosphere. This ejected material eventually settled into a thin boundary layer of rock all around the world, so geologists can actually go dig up fragments of the asteroid (or fragments of the Earth’s crust that were altered by the impact) to look for proof.

This boundary layer, called the K-T boundary, shows extreme levels of iridium and is full of ball-shaped tektites—glassy objects formed when bits of the asteroid or Earth crust melted by the impact recrystallized in mid-air and then fell back to Earth. Some clay minerals in the K-T boundary also show signs of a high-energy shock, while magnetic evidence shows that a rapid reversal of Earth’s magnetic poles may have occurred right around this time. The presence of tsunamis and soot also indicates the impact was a catastrophic global event.

However, researchers have argued over the relative influence of the impact event versus other potential drivers of extinction, including climate change (specifically, long-term global cooling), volcanic eruptions and species competition. There is even some evidence that a second asteroid impact may have occurred shortly afterwards.

To fully understand why the dinosaurs went extinct, future researchers will need to continue studying the physical and fossil records from this crucial time period in Earth’s history.