Geology You Are Watching Friends on TV

Geology

You are watching Friends on TV and Ross, a paleontologist, mentions he found a dinosaur bone that was trapped in lava 120 million years ago. Your little sister asks you how Ross knows that the dinosaur bone is 120 million years old. Answer her question using the information you learned about isotopic dating in this course.

Isotopic dating uses radioactive material to date rocks. It generally compares the presence of a radioactive isotope with the presence of its decay products. Then, using the known decay rates, this process can lead to a determination of the absolute age of the rocks being. There are different types of isotopic dating, including radiocarbon dating, potassium-argon dating, and uranium-lead dating. Therefore, Ross can compare the level of radioactive isotopes and decay products in the bone or lava to determine that it is 120 million years old.

While on a field trip to the museum for your geography class, you see some fossils on the tour. The tour guide asks how fossils can help scientists date sedimentary rocks. Tell her what you've learned about this topic from this unit course.

Certain fossils are limited to different periods of time. These fossils are known as index fossils. If an animal is known to have only lived 50-65 million years ago, then a sedimentary rock formation that contains those fossils must have been formed during that time period. Therefore, by examining the fossils in a rock formation, one can estimate when the rocks were formed. By examining several fossils, one may further narrow down the creation period by

3. On a northward trip on highway 395 on your way to Mammoth for some skiing, you pass by a sign saying that you have entered the Long Valley Caldera. Explain to your friends in the car what you've learned about how this particular area formed.

Calderas form as the result of volcanic eruptions. The most massive volcanic eruptions can eject hundreds of cubic kilometers of magma onto the Earth's surface. This magma is removed from underneath a volcano, causing the ground to subside or collapse. The resulting depression is called a caldera. The Long Valley Caldera formed in this manner.

4. On a camping trip in northeastern California you're heading into the Modoc Plateau. Your parents notice how much flatter the volcanic hills are than say Mt. Shasta or Lassen Peak. Explain to them why these volcanoes are so much shorter and wider than the one found at Mt. Shasta.

There are several different types of volcanoes. Shield volcanoes like those in the Modoc Plateau are flat and broad. Shield volcanoes are built almost entirely of fluid lava flows, which tend to make them flat and broad as the lava flows downward as it cools. In contrast, composite volcanoes, like Mt. Shasta or Lassen Peak, are tall, symmetrically shaped, with steep sides. They are so large because they are built of alternating layers of lava, ash, cinders, blocks, and bombs.