Travel Reference
In-Depth Information
they become cemented together into solid rocks, compressed by thick layers of more sediment
deposited on top.
The flat-lying sedimentary layers in the park were deposited either in shallow seas or on
land, depending upon sea level at the time. Two places to see cliffs of such rocks are at Bar-
ronette Peak near the Northeast Entrance
[GEO.2]
and at Mount Everts near Mammoth
[GEO.3].
The sedimentary rocks in these places were deposited on top of the much older
granites and gneisses between 515 and 80 million years ago. They are evidence that the ancient
mountains described above had already been eroded away to form a level plain at or near sea
level.
On the lower third of Barronette Peak's cliffs are alternating white and brown layers of sedimentary
rocks that are about 350 million years old. The chocolate-colored rocks above these are part of the
much younger Absaroka Range volcanics
[GEO.2].
More Recent History
After an incredibly long time gap, 2 billion years, Yellowstone's turbulent years began. As
many people now know, the continents move around on Earth's surface, fortunately at only a
few inches (cm) per year, by a process that geoscientists call
plate tectonics.
Yellowstone Park
is not immune to this process and, in fact, has been singled out for some special events.
he
plates
of plate tectonics are huge slabs that occupy the uppermost 60 miles (100 km)
of the solid earth. They are obliged to slide around due to the uneven cooling and heating of
Earth's interior. When Earth first formed 4.6 billion years ago, it was hot and almost entirely
molten. It has been cooling down ever since, but not evenly, since radioactive elements deep
in the earth keep adding some heat. The way the cooling takes place is illustrated in Figure
5. Parts of the interior rise, being hotter and less dense, while cooler portions sink. The plates
move around and collide with one another. This is what caused the compression that formed
the Rocky Mountains.
