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.
Petrified
Forest National Monument
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.