Grand Canyon: A Different View

Transcription

[MUSIC] Pretty awesome, isn’t it? The Grand Canyon is one of the most spectacular natural wonders on Earth, 277 miles long, 18 miles wide at its widest, and more than a mile deep into the Earth’s crust… and unlike the Great Wall of China, you can actually see it from space. All the water in all of Earth’s rivers would only fill it halfway. It almost defies belief. The Colorado river, the river that made this canyon, it’s only about 100 meters wide, that's not very big as rivers go. The Mississippi, the Amazon are far, far bigger, and they've never made anything like this. So how did it happen? No one was around to see it form, but the Grand Canyon’s story is written in those beautiful rock layers. Geologists are kind of like time traveling detectives, they look for fingerprints here and there, retrace the footsteps to retell Earth’s story, as best we can anyway. Native Americans in this area call the canyon “Kaibab”, meaning “mountain lying down” or “upside-down mountain”. They didn’t know how right they were… because down there at the bottom of the canyon, the oldest rocks are mountains. The oldest rocks at the bottom of the canyon are named after the Hindu god Vishnu. About 1.8 billion years ago, the area that’s now the Grand Canyon was covered in mountains taller than the Himalayas. But over hundreds of millions of years, erosion wore them down into hills just tens of meters tall. From this point on, the evolution of the Grand Canyon doesn’t happen in a dry desert like you see today, it happens underwater. Ancient oceans filled this area, from a billion years ago to as recently as 80 million years ago. Water would rise, and fall, and rise and fall again, depositing sand, and mud, and even ancient seashells and compressing them into rock, piling layer upon layer, turning Earth’s crust into a colorful layer cake, just waiting to be cut. You might notice we’re not at sea level right now. 70 or 80 million years ago, this whole area took a tectonic elevator ride straight up, pushing those ancient layers into a high plateau. But there was still no river, and no canyon. Northeast of here, that same uplift created the Rocky Mountains, and their snow-covered peaks. Melting snow began to flow and pool up in this area. Small rivers joined together to make larger ones, some pooled up into lakes, some even changed direction, and about 5 or 6 million years ago, the Colorado River was born. That’s not that old in geological time, but this river is special. Even though it isn’t that big,it drops 10 feet for every mile it travels, carrying half a million tons of silt and sand and rocks downstream every day. It’s like liquid sandpaper. It cut the plateau backwards, the same way a waterfall wears away at a cliff, cutting a mile-deep scar like a hot knife through butter. "Excuse me, we're trying to find the Grand Canyon" Um, here's an idea! So that’s how it got deep, but how did the canyon get so wide? Well, gravity took over, rain and ice chipping away at the canyon walls, and as it fell, it was carried downstream. Fossils and rocks from this area have even been found downstream almost as far as the Gulf of California. And that’s pretty much how we got the canyon of today. If you want to turn a mountain upside down, all you need is time. This canyon is still changing, it's getting deeper and wider, and as we continue to study it, the story of this canyon will change too. There’s stories like this locked in Earth’s crust all over the planet, hidden from view, but that little river has opened this one to us. Stay curious.