The Day the Dinosaurs Died


I had always wondered how the dinosaurs died out. I couldn’t understand how just getting hit by an asteroid, or having volcanoes spew out ash could wipe them all out. Then I heard about some research that pinpoints the moment the asteroid hit. That seemed like a promising place to start my research.

Scientists still debate the specifics of what happened, but it probably went something like this…

The dinosaurs are dead.

They died sixty-six million years ago when an asteroid the size of the island of Manhattan slammed into the ocean off the coast of Yucatan, Mexico. The asteroid punched a crater 112 miles wide and a dent one mile deep into the Earth’s surface. It caused a magnitude 11 earthquake – one of the biggest ever – to shake the Earth’s crust.

Donald E. Davis, Courtesy commons.wikimedia.org

The intense heat generated by the crash vaporized the asteroid, as well as granite in the Earth’s crust. The silica in the granite turned into molten glass.

The crust rebounded like a trampoline after the asteroid hit it. A cloud of superheated air shot into the sky at twice the speed of sound. The cloud carried the melted particles of glass into the upper layers of the atmosphere.

Within minutes after impact, the larger globs of red-hot glass began to pelt from the sky. The burning rain lasted for several hours. It started fires that burned all over the world. We can still see a layer of ash from these fires in the rocks today.

Shock waves from the impact went through the core of the planet at over ten times the speed of sound. They reached the other side of the Earth in an hour-and-a-half. The energy from these waves punched pulverized rock up twelve feet off the coast of Australia. Volcanoes in nearby India had been erupting for some time, but now their eruptions became extreme. More poisonous gasses and dust spewed into the darkening sky.

In North America, the shock waves hit the shallow, narrow gulf that stretched to the Arctic. Waves of water higher than a thirty-story building flooded the nearby land. Close on the heels of the floods, gale-force winds knocked down trees, and the molten glass began to rain onto the devastated land. Stranded fish sucked some of these glowing sand-sized particles into their gills as they gasped for breath in shallow puddles. The flood waters finally crested, then reversed course. The water rushed back, covering the dying trees, fish, and animals with mud.

An almost-mile-high tsunami raced away from the impact crater at nearly ninety miles per hour. The waves spread to every ocean in the world. They threw fish and sediments onto land. Any animals in their path were drowned.

In the next few days, the vaporized rock and volcanic ash blanketed the globe in acidic soot and dust. The toxic clouds completely blocked out the sun. Plants couldn’t photosynthesize, and died. Global temperatures dropped.

The finer dust particles remained in the atmosphere for a decade. Rain finally deposited the acidic dust into the sea. The oceans became more acidic. The acids killed most animals that required hard shells, from ammonites down to plankton. The ocean ecosystems collapsed, as well.

Seventy-five percent of all life — plant and animal — died as a result of the impact.
That was the end of the dinosaurs.

Or maybe not.

The burning winds, earthquakes, floods and fires left a few survivors scattered across the globe. But these survivors had to deal with great hardships.

The Earth was a cold, dark, hungry place in the first years following the impact. Without sunshine, plant life, including forests, died. Animals that needed trees for part of their life-cycles died, too.

The fires and darkness left little to eat – rotting trees, fungus, insects, seeds. And of course, survivors had to be able to find the food in the dark. At first, meat-eaters feasted on dead and dying animals. But soon they suffered, too, as their prey died off. Only smaller animals made it through the hungry times of the long cold night.

A decade after the asteroid hit, the skies cleared enough for shade-tolerant ferns to grow again. Eventually other plants and trees sprouted, too. The few animals who made it through the impact and years of starvation and cold finally had something to eat besides fungus, decaying trees and a dwindling number of ten-year-old seeds.

Who survived?

Sea life was impacted least. Creatures who lived deeper in the oceans suffered less than those closer to the surface.

On land, survival was more random. Those who made it through had two common traits — they were small, and they lived on the ground. This included some frogs, turtles, crocodiles, snakes and lizards. These cold-blooded animals probably survived in the tropics. It was warmer there, even in the dark.

Almost as many mammals died in the extinction as dinosaurs. Mammals evolved at the same time as the dinosaurs. But mammals had always been mouse-like creatures. They never grew to the enormous sizes of the dinosaurs.

Their small size meant that mammals required fewer calories. Being small helped them live through the hungry time. And they were used to eating more different foods than most dinosaurs, including seeds, and maybe fungi.

Early mammals lived in many different environments. The mammals that lived in trees died out when the asteroid hit. But a few scurried through the plant litter on the ground, retreating to burrows in times of danger.

As they evolved, many mammals came out in the cool night, when the cold-blooded reptiles slowed. This gave the mammals several adaptations that helped them stay alive when the asteroid hit. They had bigger eyes to see in the dark. Warm blood let them stay active in the cooler hours, and fur insulated their bodies to retain body heat. After the asteroid, their fur also may have protected the mammals from the razor-sharp edges of shattered volcanic glass that littered the ground.

Courtesy Norbert Brugge, http://www.b14643.de/Chicxulub_event/index.htm

As plant life slowly returned, mammals rebounded quickly. They adapted and filled the empty niches left by the extinction of so many other animals.

Mammals were joined in the empty landscape by a few other creatures. One tiny group of dinosaurs was able to solve the same problems that plagued mammals.
Some of these creatures were ground-dwellers, so they survived the loss of trees. They learned to lay their eggs in protected areas such as rocky ledges or hidden depressions in the soil. They had fingernail-like beaks instead of skin-covered muzzles. The hard beaks may have helped them to find seeds in the razor-sharp layer of ash laid down by the explosion.

In many ways, these animals were like mammals. They were warm-blooded. They became smaller. They made it through the decades long cold spell with a layer of insulation — feathers — that had evolved before the asteroid.

Wait … warm-blooded, beaked, egg-laying, feathered animals … sound like birds.

Red-faced mousebird, Urocolius indicus, at Pilanesberg National Park, Northwest Province, South Africa. Courtesy Wiki Creative Commons, Derek Keats, https://flickr.com/photos/93242958@N00/28386328890

Yes, birds are dinosaurs, the only group of dinosaurs to survive the asteroid extinction. Dinosaurs didn’t die out, after all.

What we’ve learned from the asteroid extinction is both reassuring and terrifying. Life can survive huge changes that happen in an instant. But there is no way of predicting who will make it through. And the life that survives won’t be the same as it was before.

The asteroid impact was the fifth global extinction the Earth has seen. We are entering the sixth, carbon dioxide global extinction. If we take action now, we can limit the loss of species, and prevent global ecosystem collapse.

But we must take action now. We must do everything we can to limit carbon dioxide production. And it must be all of us, together.

Or we can expect to go the way of the dinosaurs.

About coloradogeography

Amy Law is a science geek. She feels about science the way some people feel about music, or art, or sports – a total and complete emotional connection. She thinks in science. For Amy, there’s nothing better than helping people see the beauty of science as she does. She loves to untangle a complicated subject into its parts, explaining it so that anybody can understand what’s happening. Let her show you her world...
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