Geology of the National Parks

GeoMations and GeoClips


This week's GeoMations feature geologic time in all of its glory; first, you'll accompany Dr. Alley on his "climb" up out of the Grand Canyon and past 1.2 billion year's worth of geologic evidence. After reaching the top, you'll stop at the rim to hear a bit about the widening and narrowing of the Canyon. Then, it's back to Happy Valley, where you and Dr. Alley will hit the gridiron and witness geologic time as it marches down the field for a dramatic goal-line ending!

Next, this week's GeoClip will take you "live" to the Grand Canyon Rim, where you will join Dr. Alley in a firsthand look at "deep time." (If that clip leaves you wanting more, "part 2" is also available as an optional enrichment this week!) So, enjoy your visit to the Grand Canyon and your walk up through time. We hope you find Dr. Alley's play-by-play commentary and his incisive post-game analysis helpful in explaining what the Earth has been doing these past 4.6 billion years.


Climbing the Canyon

Climbing the Canyon
Click Here for Transcript of the Climbing the Canyon Video

At the bottom of The Grand Canyon, deep in its channel, flowing out of the page towards you is the glorious Colorado River. And next to the river, there are rocks that were sediments. They have been lava flows and other things. They have been bent in the heart of a mountain ranges. They have been intruded by granite. They have had the heck beat out of them.

And on top of them, there is an unconformity-- an erosion surface. Sitting on top of that erosion surface, there are various sedimentary rocks-- things that formed on the edges of a sea interbedded with lava flows. There are many erosion surfaces within that pile of sedimentary rocks.

And that is an immense pile of sedimentary rocks that has been dropped down by faults. If you actually try to measure the thing, you find that you get some thickness, and then you walk along the layer, and then you measure some more thickness. And the total thickness is actually about two miles of sediments in pile. And then on top of that, there is another erosion surface. That was the Grand Canyon Supergroup in that two-mile pile.

Sitting on top of this, the sea came in, and you end up with the Tapeats Sandstone, and you get the Bright Angel Shale, and you get the Muav Limestone. And then sitting on top of that, there was erosion, there are deep channels in places that were cut on top. And in those channels, one goes in and finds little bits of pockets of the Muav Limestone sitting in there. The sea had come in. The sea goes out, the sea comes back and puts in the Muav. It goes out and erodes again, and then you get the giant Redwall-- the great, massive Redwall.

And the top of that is also eroded. And it has some channels. And it wasn't until the 1980s, when, really, helicopter geology came in, that people realized that, in fact, some of those channels have little bits of limestone in them called the Surprise Canyon. The sea had gone out, it came back and put that down, it goes out, and there's erosion again.

And then sitting on top of this, we get the great rocks of the Supai. The Supai is ocean sediments-- limestones-- to the west, and it is a delta. It's up on land to the east. It's about four different units, and there's an erosion surface that goes at the end of each of those different units of the Supai.

The Supai then gave way to the mighty cliff of the Coconino. This is the sand dune rocks. This is the one that has all the beautiful tracks in it and so on. And on top of that, there's another erosion surface. Then there's sort of a mix of land and sea sediments that's known as the Toroweap that makes it a bit of a slope. And it has an unconformity and erosion surface.

And then sitting on the top of this is the cliff of the Kaibab Limestone, which gets up to the villages where you can go as a tourist. But this, in turn, slants down to the north. And underneath that, you're going to find Zion way up there, and then you're going to find Bryce, and so on, up through the giant pile of rocks.

Credit: Dr. Richard Alley

Widening and Narrowing

Widening and Narrowing
Click Here for Transcript of Widening and Narrowing Video

I was out at the Grand Canyon a few years ago. And I was standing behind the fence there. And I was talking to a very nice and knowledgeable ranger about the history of mining at the place. And we were looking at those incomparable cliffs. And there's sort of a cliff of limestone, and a slope of shale, and a cliff of sandstone on another slope, and so on, on down to the river sitting way down below someplace like that.

And while we were standing there talking, this gentleman walked up, and he asked us why the river had gotten narrower. And we gave him a confused look. And he said, well, the river down there is very narrow. But if you try to look all the way across to the North Rim which is way the heck over there, what you see is, in fact, that the top is very broad. So he sort of figured that the river had been wide, and then it had gotten narrow.

Now, right beyond the fence there was a bit of a crack down into the cliff-forming rock there. And I ask him whether he would have any interest in going out beyond that crack and taking a jackhammer and starting to work on it. And he offered the opinion that eventually it would break off. And that when it broke off, that he would end up somewhere down the slope with a big rock on top of him, and that that would not be a good thing to do.

Well, then I ask him if he looked across the canyon, did he see places where a lot of rocks had piled up that looked like they had fallen off of the cliff. And he said, well, yeah I do. And that one fell. And this was a bright person. He immediately got it. He says, oh, what happens then is that the river must cut down. And once the river has cut down some, then, this slow process of mass wasting is going to widen it.

And in particular what happens is that the shales, the slope-formers cut down. And that makes the cliffs higher. And if the cliffs get really high, they tend to fail, and blocks fall off. And so that after a while you look at it, and you find that the canyon sort of has the same shape that it used to. But it's gotten wider as well as getting deeper as the river comes down.

Credit: Dr. Richard Alley

100 Yards of Geologic Time

100 Yards of Geologic Time
Click Here for Transcript of 100 Yards of Geologic Time Video

It is 4.6 billion years ago. You were on the goal line Beaver Stadium and you have to drive 100 yards to today where you're taking Geosciences 10. The earth is forming 4.6 billion years ago. Giant meteorites are streaming in. And when they hit the surface, they make great explosions and collisions that heat the planet so much that they evaporate the ocean. And the last one of those that was big enough to evaporate the upper part of the ocean that was warmed by the sun and given energy by the sun is about 3.8 billion years ago, which leaves you 83 yards to drive to get to the goal.

Beyond this, the continents are forming. They're no longer getting blasted. And so you start to see continents show up that the cores of the modern things and they're sitting out there very nicely. And they are formed so that you get an idea of what the world is going to be like by about 2.5 billion years ago, which is a mere 54 yards to get your touchdown.

There are bacteria in the ocean and the bacteria are committing acts of flatulence. They're putting oxygen up. The oxygen changes the composition of the atmosphere, it changes the oceans, and it eventually allows bigger critters to appear. And those bigger creators include shelly critters which suddenly make lots of interesting rocks, limestones. And so you start to get lots of shells showing up about 570 million years ago, which is a mere 12 yards to get the goal line. The shells are doing really well.

And then there's a really bad day. The ocean gets very warm from greenhouse and it belches out bad gases and most of the things alive die. And that happens about 225 million years ago at the end of the Paleozoic which is only five yards from the goal.

That clears up space so that you start to get dinosaurs. And as you know, dinosaurs were really big and they're sort of cute critters. And so you start getting dinosaurs in the Mesozoic. And here is a dinosaur if you would like one. and the dinosaurs are having a fine time and they're smiling a lot.

But there's another meteorite coming. And so the big meteorite comes screaming in and it kills the dinosaurs, and that changes the world a lot. And that happens about 65 million years ago which is only one and a half yards from the goal.

That makes room for mammals to show up, and so you start to see mammals such as this elephant that you're about to see here. This elephant happens to be running away from you. And the elephant has some big ears and a really curly tail.

And that comes up to recorded history. And recorded history, 6,000 years ago, just a little over the thickness of a sheet of paper.

And finally, to the culmination of creation to you, who are born about 1/200th of the thickness of a sheet of paper from the goal line today.

Credit: Dr. Richard Alley


The vast and varied history of the planet is best experienced by hiking the Canyon, but you can see a lot of the story from the rim. Here, you'll get a very brief overview of a very long story. ( Click the link to view movies - All are in QuickTime format )

#1: Supergroup Part 1: Grand Canyon Rim

Supergroup Part 1: Grand Canyon Rim
Click Here for Transcript of Supergroup Part 1: Grand Canyon Rim

The really cool thing here is how much extra time we can see. If we look down just to the left of where we see the river in the shadow of the cloud right now, we'll see that there are layers that are slanting. And then above them there are layers that are horizontal. Now the slanting layers are the Grand Canyon Super Group.

They are rocks that were deposited between about 1.2 billion years ago and about 0.7 billion or 700 million years ago. If you add up the thicknesses of all of those going down it's almost three miles of sediment-- almost three miles. Now we've got a mile on top and then from our feet down to the unconformity.

Then there's three miles of sediment under that. And then if we peer down the canyon in that deep cut down there are the the old crystalline rocks, the old beautiful rocks that were cupped in the heart of a mountain range that are lava flows and sediments that add up to many more miles of rocks. And those have been cut. And that it was eroded. And then these were put on top.

And then faults that are sort of like Death Valley faults broke and dropped these down. And then it eroded on top. And then these were came And then those were deposited. And then those were eroded away. And then the river cut through. And it's so cool. And it's just this immense story that just keeps being told over and over and over.

Credit: Dr. Richard Alley

Want to see more?

Optional Enrichment (no, these won't be on the quiz!):

Supergroup Part 2: Grand Canyon Rim(Transcript)

Deep Time film clips - What do beauty, saving money at Las Vegas, religion, oil exploration, emerging new diseases, and the planet’s recovery from global warming have in common? All in some way involve deep time, the immense age of the Earth. Eric Spielvogel filmed a discussion of these and other issues with Dr. Alley, for a special “time” issue of Research! Penn State. These "Deep Time film clips" will give you something to think about, and may even help with the course. Enjoy!