Day of Doom

The worst day in the history of planet Earth began like any other. 

As the sun rose, the loud buzzing of bloodsucking flies filled the muggy air. A warm mist hung over the thick forests. And prowling through the jungle, squishing the ground with each heavy step, was a huge monster covered in dark scales and scraggly fuzz. This was the most fearsome of all dinosaurs: Tyrannosaurus rex (or T. rex). Sniffing the air, the creature let out a deep, loud growl. Its enormous mouth flashed more than 50 razor-sharp teeth as long as bananas.    

It was 66 million years ago in western North America. And the world was about to change forever. 

All of a sudden, the ground beneath the T. rex began to shake so powerfully it seemed as if it were crumbling. Burning rocks rained down from the sky. The air turned so hot that trees everywhere burst into flames.

To the clueless T. rex in the jungle, it must have looked like the world was ending. And in some ways, it was. 

By the time the destruction had quieted down, the T. rex—along with countless other dinosaurs and creatures—was dead. The landscape was in ruins. Life on Earth would never be the same.

The worst day in the history of planet Earth began like any other. 

Flies buzzed as the sun rose. A warm mist hung over the forests. And stomping through the jungle was a huge monster covered in dark scales and thin fuzz. This was the scariest of all dinosaurs: Tyrannosaurus rex (or T. rex). The creature sniffed. It growled and showed its 50 sharp teeth as long as bananas.    

It was 66 million years ago in western North America. And the world was about to change forever. 

Suddenly, the ground began to shake powerfully. Burning rocks fell from the sky. The air turned so hot that trees burst into flames.

To the T. rex, it must have felt like the world was ending. And in some ways, it was. 

By the time the destruction had quieted, the T. rex—along with most other dinosaurs and creatures—was dead. The land was in ruins. Life on Earth would never be the same.

Before this disaster shook the planet, dinosaurs had walked the earth for more than 150 million years. Scientists call this time the age of the dinosaurs. 

At first, dinosaurs were not the giant, scary beasts we’re used to seeing in movies. They started out small and lightweight. “They were only about the size of dogs,” says Steve Brusatte. He’s a paleontologist, a scientist who studies ancient animals and plants.

But over time, dinosaurs grew larger and spread all over the world. If you’d been around back then, you would have stared in awe at the titanosaurs (tye-TAN-uh-sors) stretching their long necks to munch on the leaves of the tallest trees. Some weighed more than nine large elephants put together. You would have felt the ground rumble as a herd of Triceratops (trye-SEHR-uh-tahps) lumbered by. These tanklike creatures had a sharp horn above each eye and another one on their beaky nose.

And of course, you would have cowered as you came across the king of all dinosaurs, the largest meat-eating animal ever to stalk the land: T. rex. About the size and weight of a school bus, T. rex attacked its prey silently. Its short, strong arms had knifelike claws to hold down its victims and pierce scaly flesh. One powerful bite could crush through bone. 

T. rex and other dinosaurs ruled over the land, gobbling up all types of animals and plants. That is, until about 66 million years ago, when dinosaurs simply vanished.

Before this disaster, dinosaurs had lived on Earth for more than 150 million years. Scientists call this time the age of the dinosaurs. 

At first, dinosaurs were not big and scary like the ones we see in movies. They started out small and light. “They were only about the size of dogs,” says Steve Brusatte. He’s a paleontologist. That’s a scientist who studies very old animals and plants.

But over time, dinosaurs got larger. They spread all over the world. If you’d been around back then, you would have been amazed by the long necks of the titanosaurs (tye-TAN-uh-sors). Some weighed more than nine large elephants. You would have felt the ground shake as a group of Triceratops (trye-SEHR-uh-tahps) walked by. Each of these creatures had three sharp horns.

And of course, you would have felt fear if you had met the largest meat-eating animal on land: T. rex. About the size and weight of a school bus, T. rex attacked its prey silently. Its short, strong arms had sharp claws to hold and pierce its victims. One powerful T. rex bite could crush bone. 

T. rex and other dinosaurs ruled over the land. Then, about 66 million years ago, they vanished. 

For a long time, experts didn’t know why the dinosaurs disappeared. Then in the 1970s, a curious American scientist named Walter Alvarez became determined to solve one of the world’s greatest mysteries. 

Alvarez didn’t actually study dinosaurs. He was a geologist—his specialty was rocks. The layers of rock beneath our feet are like a thick history book telling the story of our planet. Rocks get older as you move deeper and deeper underground, each layer a different chapter in Earth’s past. Some contain fossils of long-gone animals and plants. Others hold clues to ancient landscapes and weather.

By analyzing rocks, scientists had realized that something had happened about 66 million years ago. When they looked at the layers of rock from before that time, dinosaur fossils were everywhere—bones, eggs, claws, teeth, even poop. But none existed in the layers of rock after that time. How could that be possible?

It was well known that animals could become extinct. Some scientists thought that dinosaurs had died out because the planet had gotten too cold. Or perhaps it had gotten too hot. Or maybe dinosaurs had spent so much energy growing so big that they had no energy left to survive. 

Whatever had happened, most scientists thought it had happened slowly, over millions of years. Up until the 1970s, it was believed that no single disaster could quickly lead to doom for animals everywhere. 

But what if it could?

One of the first to ask that question was Walter Alvarez. And he didn’t stop until he had the answer.

For a long time, experts didn’t know why dinosaurs disappeared. Then in the 1970s, an American scientist named Walter Alvarez wanted to solve this mystery. 

Alvarez didn’t actually study dinosaurs. He was a geologist—a rock expert. The layers of rock under our feet are like a thick history book. They tell the story of our planet. Rocks get older as you get deeper underground. Each layer is like a different chapter in Earth’s past. Some contain fossils of long-gone animals and plants. Others hold clues to old landscapes and weather.

By studying rocks, scientists had noticed that something had happened about 66 million years ago. When they looked at the layers of rock from before that time, dinosaur fossils were everywhere. They found bones, eggs, claws, teeth, even poop. But none of that was found in the layers of rock after that time. How
could that be?

It was well known that animals could become extinct. Some scientists thought that dinosaurs had died out because the planet had gotten too cold or too hot. Or maybe dinosaurs had spent so much energy growing
so big that they had no energy left to live. 

Whatever had happened, most scientists thought it had happened slowly. They thought it had taken millions of years. Up until the 1970s, it was believed that no one disaster could quickly lead to death for animals everywhere. 

But what if it could?

One of the first to ask that question was Walter Alvarez. And he didn’t stop until he had the answer.

Alvarez’s obsession with dinosaurs—and the mystery of their disappearance—first began in the European country of Italy. He was there on a research trip in the early 1970s. Like other scientists before him, Alvarez noticed a 1-inch layer of dark, soft clay. This layer was sandwiched between the fossil-rich rock from the time of the dinosaurs and the barren rock layers after dinosaurs were gone. 

What was that thin layer of dark clay? If rocks were like a history book, the layer of dark clay felt to Alvarez like an important page. But he had no idea how to read it. So he called his father, Luis, for help. 

Luis Alvarez was also a scientist, and he was known for thinking outside the box. He suggested testing the clay to learn more about what it was made of and how it had formed.

What the two men discovered came as a complete surprise: The clay was chock-full of a metal called iridium (ih-RI-dee-uhm). The metal is very rare on Earth’s surface—but a lot of it is found in space. What could possibly explain all that iridium? 

And it wasn’t just in the clay in Italy. Alvarez traveled to Denmark, another country in Europe, and also found the metal there in clay dating to the same exact time.

Alvarez’s interest in dinosaurs—and the mystery of how they disappeared—first began in the European country of Italy. 

He was there on a research trip in the early 1970s. Like other scientists before him, Alvarez noticed a 1-inch layer of dark, soft clay. Below this layer was the rock filled with fossils from the time of the dinosaurs. Above it were the barren rock layers from after the dinosaurs were gone. 

What was that thin layer of dark clay? If rocks were like a history book, the layer of dark clay felt to Alvarez like an important page. But he had no idea how to read it. So he called his father, Luis, for help. 

Luis Alvarez was also a scientist. He was known for thinking outside the box. He suggested testing the clay to learn more about what it was made of and how it had formed.

What the two men found was a big surprise: The clay was full of a metal called iridium (ih-RI-dee-uhm). The metal is very rare on Earth. But a lot of it is found in space. What could explain all that iridium? 

And it wasn’t just in the clay in Italy. Alvarez traveled to Denmark, another country in Europe. He found the metal there in clay from the same exact time. 

Alvarez spent many sleepless nights tossing and turning, thinking about all the possible explanations. But only one made sense: If there’s a lot of iridium in space, maybe the metal had come from there. Maybe a giant space rock, called an asteroid, had slammed into Earth, spraying iridium all over the planet. Maybe an asteroid was to blame for the dinosaurs’ extinction.

In 1980, Alvarez officially published his and his father’s research for all scientists to read. It stirred up a storm of confusion and disbelief. For decades, scientists had believed that all changes on Earth happen gradually—that new animals and plants appear and die out over millions of years. And while most do, Alvarez realized that the dinosaurs might be an exception.

“Walter’s theory was a big deal,” says Brusatte. “At first, it was controversial. Most scientists did not accept it.”

But by the late 1980s, more findings seemed to confirm the asteroid idea. High levels of iridium were discovered all over the world in rocks from the time of the extinction. Many of those same rocks also contained tiny balls
of glass that are usually formed by the intense heat of an asteroid crash. Slowly, more and more scientists started to agree with Alvarez.

Alvarez thought hard about all the possible reasons. But only one made sense: If there’s a lot of iridium in space, maybe the metal had come from there. Maybe a giant space rock, called an asteroid, had hit Earth.
It might have sprayed iridium all over the planet. Maybe an asteroid caused the dinosaurs’ extinction.

In 1980, Alvarez published his and his father’s research for all scientists to read. It caused a storm of confusion and disbelief. For decades, scientists had thought that all changes on Earth happen gradually. They thought that animals and plants appear and die out over millions of years. And while most do, Alvarez realized the dinosaurs might be different.

“Walter’s theory was a big deal,” says Brusatte. “At first . . . most scientists did not accept it.”

But by the late 1980s, more findings seemed to support the asteroid idea. High levels of iridium were found all over the world in rocks from the time of the extinction. Many of those same rocks also had tiny balls of glass. These glass balls are usually made by the high heat of an asteroid crash. Slowly, more scientists started to agree
with Alvarez. 

Then in 1991, the most convincing clue of all was found: an enormous crater mostly buried under the sea off the coast of Mexico, dating to 66 million years ago. Only one thing could have made a hole that big in the ground—a giant space rock. 

“It was a bombshell,” Alvarez later wrote. 

The crater helped to finally confirm Alvarez’s theory. It also allowed him and other scientists to figure out just how massive the asteroid was—bigger than the tallest mountain on Earth, Mount Everest. 

A space rock that huge would have instantly killed and destroyed everything within 600 miles of where it hit. But the destruction didn’t end there. Within minutes, the crash triggered earthquakes more powerful than those ever felt by humans. Waves three times as tall as the Empire State Building slammed into coasts. Wildfires began burning and didn’t stop. 

In fact, the disaster was just beginning. 

Ash from the fires and dust from the impact covered the planet like a blanket, blocking sunlight. For years, the globe was shrouded in darkness. In this cold, dark world, plants couldn’t grow. Any animals that had survived the asteroid crash were now caught in a deadly chain reaction. Without plants, plant eaters starved to death. Then meat eaters came next. 

Today scientists think that three out of every four species on Earth died. Just like that, the age of the dinosaurs was over.

Then in 1991, the biggest clue of all was found: a huge crater. It was mostly buried under the sea near Mexico. It was from 66 million years ago. Only a giant space rock could have made a hole that big in the ground. 

“It was a bombshell,” Alvarez later wrote. 

The crater helped finally confirm Alvarez’s theory. It also let him and other scientists figure out how big the asteroid was. It was bigger than the tallest mountain on Earth, Mount Everest. 

A space rock that huge would have instantly killed and destroyed everything within 600 miles of where it hit. But the destruction didn’t end there. Within minutes, the crash started powerful earthquakes. Super-tall waves hit coasts. Wildfires began burning and didn’t stop. 

In fact, the disaster was just beginning. 

Ash from the fires and dust from the impact covered the planet like a blanket. They blocked sunlight. For years, the globe was dark. In this cold, dark world, plants couldn’t grow. Any animals that had survived the asteroid crash were now caught in a deadly series of events. Without plants, plant eaters starved to death. Meat eaters died next. 

Today scientists think that three out of every four species on Earth died. The age of the dinosaurs was over.

But slowly, over thousands of years, the planet recovered. As the darkness lifted, sunlight started to stream across the scarred land. Seeds began to sprout and grow into thick forests. 

In this new world, there was no T. rex crashing through the trees. But there were survivors: turtles, frogs, crocodiles, snakes, fish, and birds that had found shelter underground or deep inside caves and ponds. And there were mammals too. 

After the dinosaurs were wiped out, mammals had the chance to take over the world. Many different types of mammals slowly appeared and spread far and wide—rats, sloths, bears, monkeys . . . and eventually, humans. We are also mammals. 

And it’s likely that we wouldn’t be here if it weren’t for that day of doom 66 million years ago. Or maybe we would. We would just have to share our world with a T. rex prowling around our backyard.

But slowly, over thousands of years, the planet healed. There was sunlight again. Plants began to grow. 

In this new world, there was no T. rex. But there were survivors: turtles, frogs, crocodiles, snakes, fish, and birds. 

They had hidden underground or deep inside caves and ponds. And there were mammals too. 

After the dinosaurs were gone, mammals had the chance to take over the world. Many types of mammals slowly appeared and spread. There were rats, sloths, bears, monkeys . . . and eventually, humans. We are also mammals. 

And it’s likely that we wouldn’t be here if it weren’t for that day of doom 66 million years ago. Or maybe we would. We would just have to share our world with a T. rex walking around in our backyard.