Have you ever visited the Grand Canyon?
Many who do spend less than a day viewing the scenery from a few of the scenic overlooks and they leave with the belief that they have seen the Canyon. Have they really seen it?
Do people who stop and look for a few minutes and take some pictures really know what they are looking at?
When you finish this lesson the answer to the question should be obvious.
Is there anything in this picture which you think could be evidence for change? For another picture of the Grand Canyon click the name.
You may look at fossils to find evidence of what the Grand Canyon was like millions of years ago. Click the word "Fossil" to see one which is located on the South Rim of the Grand Canyon.
What kind of living organism does this fossil
remind you of?
What is the environment like for the living organism you thought of?
Here is another fossil for you to look at. It is also found on the South Rim of the Grand Canyon. Consider that the elevation of the South Rim is over 7,000 feet above sea level. Click the words "Another Fossil" to see this second one.
You may not recognize this fossil. It is
called a "Crinoid" or "Sea Lilly."
With a name like that you can probably guess what kind of environment it lived in.
What do these fossils tell you about the environment where the organisms once lived in the place that is now the Grand Canyon?
Try to explain why we find evidence of organisms that lived on the bottom of an ocean in rocks that are over 7,000 feet above the current sea level?
Let's look at some more evidence. Not far from the Grand Canyon is another very interesting place: the Petrified Forest National Monument. Click the name of this Monument to see something similar to the Grand Canyon but this time you will have a closer view.
What do the lines in the hills represent?
You can see similar lines in the rocks of the Grand Canyon. What do they suggest about the formation of rocks we see in the cliffs of the Canyon?
The rocks near the bottom of the Grand Canyon are part of ancient mountains which were formed when the earth was only half its present age. That would make them slightly less than 2 billion years old.
Since we are concerned with changes in the Canyon we could ask a question about its location: Has the site where the Grand Canyon exists today always been in the same place? Let's take a look. Click the words "map" to see where this location has been. "MYA" on the map stands for "Millions of Years Ago." The red dots mark the location of the Grand Canyon at each specified time in geologic history.
You have seen evidence which shows that an ocean covered the place which is now the Grand Canyon. Actually, there have been several shallow oceans in this location and each is represented by a layer of rock. Between the ocean layers are different rocks that show another type of environment existed after one ocean dried up and before another formed. Once again we have fossil evidence to show what that environment must have been like. Click "tracks" to see more evidence.
These tracks were made by a reptile. Based
upon this new evidence we can envision that during the times when the oceans
were not present and the area was warm and dry. How do we know this?
Now that you have seen evidence which shows the Grand Canyon has been changing over time for millions of years let's take a look at a diagram to see the age of each layer. You are going to see a profile of the Canyon--a drawing that shows what it would look like if we could cut through the walls. Click "Profile" to see the diagram.
Now what do you think? Do the people who
spend one day looking at the Grand Canyon and taking pictures from viewpoints
along the rim really know what they are seeing?
More important, however, is that you have a much clearer picture of the geologic history of the Grand Canyon and you have seen evidence that shows changes occur over millions of years.
When you go to see the Grand Canyon try to imagine the changes. Walk down a trail for a while and look for evidence of the layers. If you go with a ranger, she or he will be able to point out old ocean and desert layers. Don't forget to look for fossils.
Remember, too, that the Canyon is still changing and will continue to do so. It just happens so slowly that we don't notice any differences from one visit to the next.