Geologic Time

Scientists chose where units of geologic time began and ended based on the appearance or disappearance of life.

• true

• false

Which of these choices is the best definition of absolute dating?

• determining the age of a rock layer by studying the fossils present

• finding the age of an object compared to other objects

• measuring the age of an object in years using any method

• determining the amount of a radioactive isotope in an object

What is the method of measuring age that gives the most precise results?

• radioactive dating, when scientists measure the levels of an isotopic element inside of an object

• rate of sedimentation, which dates layers of Earth based on their thickness

• law of superposition, which dates layers of Earth based on their order

• B. relative dating, when scientists fill an object with carbon and measure how much will fit

Which method determines the relative age of Earth's sedimentary layers based on their organization?

• rate of sedimentation

• law of suspension

• radioactive dating

• Fossil Comparison

Which of these choices is an example of the way a geologist would use

relative dating (The Law of Superposition)?

• determining the minerals that make

  up rocks

• placing rock layers in order of

  oldest to youngest

• classifying rocks as igneous,

  sedimentary, or metamorphic

• using radioactive isotopes to

  determine the exact age of rock samples

. Which of these statements describes what happens during radioactive decay?

• A Stable isotope interacts with an unstable isotope

• A stable isotope breaks down and becomes unstable

• An unstable isotope breaks down into a more stable isotope.

• An unstable isotope interacts with another unstable isotope.

How would a geologist determine the age of mountains formed by the upwelling of igneous rock?

• use radioactive dating to date water in a lake in the mountains

• use radioactive dating to date Earth's outer core below the mountains

• use radioactive dating to date only the bedrock underneath the mountains

• use radioactive dating to date the igneous rock and the topmost layer of soil

Limestone can be found at the top of the Himalayas, the highest mountain range in the world. Limestone is a rock that usually forms at the bottom of shallow, warm waters. What does this information show about Earth?

• It shows that Earth has not changed much over the years as limestone has adapted to forming on mountain peaks.

• It shows that Earth has evolved over time as areas of land that have once been covered in water, but no longer are.

• It shows that Earth circulates its minerals so often that limestone always ends up on the peaks of mountains.

• It shows that Earth has mostly convergent plate boundaries that push limestone from the ocean floor to the top of mountains.

At one time, several kinds of camels lived in Florida. The evidence comes from fossils found in Florida. Which of these objects would be a fossil that shows that camels once lived in Florida?

• Sinkhole formed by a retreating glacier

• sedimentary rock that formed a long time ago

• crystal formation suspended from the ceiling of a cave

• remains of an organism preserved by geologic processes

The timeline above shows changes that occurred in the Sahara Desert throughout history.

What does this timeline suggest about Earth?

• It suggests that Earth has changed over time since human fossils became present in the Sahara after 9,000 years, indicating that the environment had been suitable enough to support human life at one time.

• It suggests that Earth has not changed much over time since human fossils were present as early as 9,000 years ago, indicating that Earth's environment has almost always been suitable for the presence of life.

• It suggests that Earth's deserts always receive monsoon rains every 1,000 years.

• It suggests that Earth is only able to preserve fossils in environments that are desert like.