Day of Doom

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

It was 66 million years ago in North America. The sun rose in the sky. Flies buzzed in the air. A warm mist hung over the forests.

Stomping through the jungle was a huge monster covered in dark scales and thin fuzz. This was the scariest of all dinosaurs: Tyrannosaurus rex (T. rex). It growled and showed its 60 sharp teeth. Each was as long as a banana.

Suddenly, the ground began to shake. 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. The T. rex—along with most other dinosaurs—would soon be extinct.

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

It was 66 million years ago in North America. The sun rose in the sky. Flies buzzed in the air. There was a warm mist in the forests.

A huge monster was stomping through the jungle. It was covered in dark scales and thin fuzz. This was the scariest of all dinosaurs. It was the Tyrannosaurus rex (T. rex). It growled and showed its 60 sharp teeth. Each was as long as a banana.

Then the ground began to shake. Burning rocks fell from the sky. The air turned very hot. Trees burst into flames.

To the T. rex, it must have felt like the world was ending. And in some ways, it was. The T. rex and most other dinosaurs would soon be extinct.

Before this disaster, dinosaurs had roamed Earth for millions of years. Scientists call that time the age of the dinosaurs. At first, dinosaurs were not big and scary like the ones we see in movies. They started small—about the size of large dogs!

Over time, dinosaurs got larger and spread all over the world. There were huge titanosaurs (tye-TAN-uh-sors) that stretched their long necks to eat from the tallest trees. There were horned Triceratops (trye-SEHR-uh-tahps) that shook the ground as they stomped by. And of course, there was the largest meat-eating animal ever to walk the land: T. rex. It was about the size and weight of a school bus!

T. rex and other dinosaurs ruled the land. And then they vanished.

Dinosaurs had roamed Earth for millions of years before this disaster. Scientists call that time the age of the dinosaurs. At first, dinosaurs were not big and scary like the ones we see in movies. They started small. They were about the size of large dogs!

Dinosaurs got larger over time. They spread all over the world. There were huge titanosaurs (tye-TAN-uh-sors).They stretched their long necks to eat from the tallest trees. There were horned Triceratops (trye-SEHR-uh-tahps). They shook the ground as they stomped by. And of course, there was the T. rex. It was the largest meat-eating animal ever to walk the land. It was about the size and weight of a school bus!

T. rex and other dinosaurs ruled the land. And then they vanished.

Fast-forward to the mid-1900s. During this time, experts didn’t know what happened to the dinosaurs. But scientists were finding some clues by studying rocks.

The layers of rock under our feet are like a thick history book. They tell the story of our planet. Rocks are older as you get deeper underground. Each layer is like a different chapter in Earth’s past. Some hold fossils of animals and plants from long ago.

In the 1970s, an American scientist named Walter Alvarez was studying rocks from millions of years ago. Like other scientists before him, Alvarez saw layers of rock filled with fossils from the time of the dinosaurs. Above it, he saw empty rock layers with almost no fossils. That was from after the dinosaurs were gone. In between these layers was a thin layer of soft clay.

If rocks were like a history book, the layer of clay seemed 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 creatively. He suggested testing the clay to learn more about it. What the two men found was a big surprise.

The clay was full of a metal called iridium (ih-RIH-dee-uhm). The metal is very rare on Earth. But a lot of it is found somewhere else—in outer space.

Walter Alvarez thought hard about what this could mean. Only one idea made sense: If there’s a lot of iridium in space, maybe that’s where the metal had come from!

Maybe a giant space rock called an asteroid had slammed into Earth. It would have scattered iridium all over the planet. Maybe a space rock led to the disappearance of the dinosaurs!

Fast-forward to the mid-1900s. During this time, experts didn’t know what happened to the dinosaurs. But scientists were finding some clues by studying rocks.

There are layers of rock in the ground. They are like a thick history book. They tell the story of our planet. Rocks are older as you get deeper underground. Each layer is like a different chapter in Earth’s past. Some layers have fossils of animals and plants from long ago.

In the 1970s, an American scientist was studying rocks from millions of years ago. His name was Walter Alvarez. Like other scientists before him, Alvarez saw layers of rock. They were filled with fossils from the time of the dinosaurs. Above it, he saw empty rock layers with almost no fossils. That was from after the dinosaurs were gone. In between these layers was a thin layer of soft clay.

This layer of clay seemed to Alvarez like an important page in Earth’s history book. 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 creatively. He suggested testing the clay to learn more about it. What the two men found was a big surprise.

The clay was full of a metal called iridium (ih-RIH-dee-uhm). This metal is very rare on Earth. But a lot of it is found somewhere else: in outer space.

Walter Alvarez thought hard about what this could mean. Only one idea made sense. If there’s a lot of iridium in space, maybe that’s where the metal had come from!

Maybe a giant space rock called an asteroid had hit Earth. It would have scattered iridium all over the planet. Maybe a space rock led to the disappearance of the dinosaurs!