Earth science for 8th Grade

The fossil record can reveal changes in the environment over time. Scientists have found fossils of marine animals on the tops of mountains in Canada. What does this tell us about the history of the environment in that area?

• The mountains were once sediment at the bottom of an ocean.
• The ancient environment in the area did not favor fossilization.
• The ancient environment in the area was much drier than it is today.
• The mountains formed before the animals died, and their remains were fossilized.

The graph shows how radioactive decay occurs in a 4-milligram (mg) rock sample that contains fossils. The unstable atoms in the sample have a half-life of 1.3 billion years. When the rock forms, the atoms are all unstable. After one half-life, the atoms of 2 mg of the sample are unstable. How much time will have passed after three half-lives?

• 0 years
• 650 million years
• 2.6 billion years
• 3.9 billion years

A paleontologist is studying fossils of ferns from the Cenozoic era. Species A Is abundant in older rock layers. In younger rock layers, however, Species A disappears and other species of ferns become abundant. Which is the best hypothesis for why Species A disappeared?

• Ferns became less abundant during the Cenozoic era.
• Ferns did not have the resources they needed during the Cenozoic era.
• Species A disappeared after a mass extinction event caused the extinction of all ferns.
• Species A became extinct because of increased competition from other species of ferns.

The illustration above shows Tropites marine mollosks similar to squids that had called shells and that lived between 230 and 208 million years ago. Fossils of these mollusks are now found in rock layers throughout the world. Why are Tropites particularly useful to geologists and paleontologists?

• They existed for a relatively long period of geologic time, and they can be used as index fossils.
• They existed for a relatively short period of geologic time, and they can be used as index fossils.
• They existed for a relatively long period of geologic time, and they can be used as examples of Cenozoic era fossils.
• They existed for a relatively short period of geologic time, and they can be used as examples of Paleozoic era fossils.

Which of the following organisms will most likely become a fossil?

• a plant covered by a lava flow
• a small lizard covered by tree sap
  
• a deer killed and eaten by predators
  
• a bacterium dead on the bottom of the ocean

A scientist is trying to determine the age of a fossil. If the scientist wants to find the fossil's age in years, which method should she use?

• The scientist should examine the rock layers.
• The scientist should examine atoms in the rock.
• The scientist should examine the fossil's position in the rock
• The scientist should examine how deep in the rock the fossil was located.

Which of the following is not a trace fossil?

• tracks
• burrows
• ammonites
• coprolites

_______________ is the idea that older rock layers can be found below younger rock layers in undisturbed geologic columns.

• principal of original horizontality
• principal of superposition
• principal of cross-cutting relationships
• principal of unconformities

Where are older rock layers found?

• on top of younger rock layers
• under younger rock layers
• near igneous intrusions
• near faults

Which of the following is an index fossil?

• brachiopods
• tyrannosaurus rex
• coprolites
• trilobites