Chapter 7: The Grand Canyon
When you visit a mountain, you arrive at the bottom, and you look up at the mountain. But when you visit a canyon, you can often arrive at the top, and look down into the earth. And when you look down into the Grand Canyon, you look down a long way. At the bottom, which in most places is about 1.2 kilometres below you, you see the Colorado River. But when you look at the tall, red sides of the canyon, you are looking at a wonderful story – the story of how the earth was made.
The Spanish word colorado means ‘full of colour’. This describes the Grand Canyon very well. It is not the river that is full of colour – it is the canyon itself. Its walls are made of layers of
stone – some red, some yellow, and some brown or orange. Each layer of stone lies on top of the other layers like a great sandwich.
And this is how the canyon was made – just like a sandwich. But this sandwich began nearly 2 billion years ago!
At that time, the world was a very different place. No animals lived on the land, and there were only a few in the sea. The land was different too. Where North America is now, there was a large piece of land called Laurentia. Then some new islands, made of very hard stone, pushed up out of the sea. Slowly – during about the next 200 million years – they moved across the sea. In the end, they crashed into Laurentia, and stayed there. They were the first layer – the bottom layer – of the sandwich. Now we call them the Vishnu
Basement Rocks.
There are nearly forty different layers of rocks in the walls of the Grand Canyon. We usually describe them in three groups of layers: the Vishnu Basement Rocks, the Grand Canyon Supergroup Rocks, and the Layered Paleozoic Rocks (Paleozoic means ‘Old Life’). The second group, the Supergroup, was even slower than the first. It took them about 700 million years to arrive. And they could not stay still. They moved
around, and fell over – slowly – until the next group of rocks arrived.
The final group is the top layer in the sandwich – the flat layers of red, yellow, and brown rock. They did not move around. They stayed flat, and that is why they make interesting pictures. Everyone who visits the Grand Canyon takes pictures of these layers!
Most of this story happened under the sea – that is where many of the layers were made. And then, about 75 million years ago, something big happened. Something pushed the land up out of the sea. It made the Rocky Mountains, and it pushed the Grand Canyon three kilometres up out of the sea.
Of course it was not a canyon then. It was a piece of flat land, hard and dry, like the top of a table. But the land moved a little, and a river – the Colorado River – started to move across the land and to cut very slowly down into the rock. That was about 7 million years ago. Now the Grand
Canyon is 446 kilometres long and from 6 to 29 kilometres across. And when you look at it, you are looking at the long, slow story of the earth.