Fossil & Earth's History

In 1980, scientists found that a certain layer of rock contained more than usual amounts of clay with the element iridium. Scientists determined that the rock in this layer was about 65 million years old. An image of this rock layer is shown below. The scientists have also found the following three pieces of evidence.

1. Evidence of dinosaur fossils were found in rock layers older than the iridium layer.

2. Evidence of dinosaur fossils were NOT found in rock layers younger than the iridium layer.

3. Iridium is not found in high concentrations in Earth layers but is abundant in asteroids.

What does this information most likely show about Earth's history and dinosaurs?

• Iridium was produced on Earth's surface by sedimentation and killed off the dinosaurs.

• Iridium was produced on Earth's surface by sedimentation and helped dinosaurs thrive

  on Earth.

• A large asteroid collided with Earth and killed off the dinosaurs.

• A large asteroid collided with Earth and helped dinosaurs thrive on Earth.

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What can be told about the age of the fossils in the diagram?

• The fossils in layer 5 are the oldest, and the fossils in layer 1 are the youngest.

• Nothing about the ages of the fossils can be determined from the diagram.

• All of the fossils are the same age because they were all present during the same

  period.

• The fossils in layer 1 are the oldest, and the fossils in layer 5 are the youngest.

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Consider the diagram of the geologic time scale below. A scientist found the fossilized remains of a modern badger species in a new layer of sedimentary rock. The fossil was dated to the Holocene geologic epoch. If the scientist wanted to find an ancestor of this species from the Pleistocene geologic epoch, where should she look?

• in a layer of rock above the badger fossil, since younger layers are usually higher

• in the same layer of rock in which the badger fossil was found, since related organisms

  are usually together

• in a layer of rock below the badger fossil, since lower layers are usually older

• in a layer of rock known to be from the Eocene geologic epoch that is at another

  location

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The diagram below shows an index fossil that was found in one of several layers of sedimentary rock.

Which of the following best describes the relative age of the rock in layer D?

• It is younger than the index fossil found in layer D.

• It is older than the index fossil found in layer D.

• The relative age of the rock cannot be determined.

• It is the same age as the index fossil found in layer D.

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Geologists have used the principle of superposition to determine that deeper layers of rock are usually older than shallower layers of rock.

A dating system that describes only the order in which rocks were formed is called

• relative dating.

• absolute dating.

• radioactive dating.

• numerical dating.

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While examining a layer of rock, a scientist found a fossil of a trilobite like the one shown below. The scientist knows that trilobites only lived during the Paleozoic era.

The scientist finds fossilized remains of other species in the same rock layer as the trilobite. What can the scientist conclude about these other fossils?

• The organisms that formed them are still living in modern times.

• The organisms that formed them must have evolved from trilobites.

• The organisms that formed them likely also lived during the Paleozoic era.

• The organisms that formed them likely went extinct before the Paleozoic era.

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The diagrams below represent rock layers found in two different locations by two different scientists. The scientist at location X used letters to label his rock layers, while the scientist at location Y used roman numerals to label her layers. Examine these diagrams and then answer the question that follows.

The scientists both used the same colors and patterns to represent different types of rocks. They also used the same set of black-and-white symbols to represent specific types of fossils in the layers. By correlating layers based on fossils and rock types, the two scientists have discovered that certain rock layers are present in both locations.

Based on this information, if the age of layer R is 260 million years, then what other layer likely also has an age of 260 million years?

• II

• S

• Q

• VI

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Index fossils are found throughout the world and come from organisms which existed during limited periods of geologic time. Which of the following best describes what index fossils can be used to determine?

• when an organism first appeared on Earth

• how an organism evolved over time

• the way an organism went extinct

• the age of a layer of rock

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Jenny finds a sample of a mineral known as zircon in a sample of rock material. She takes it back to her laboratory and measures the amount of radioactive uranium in it compared to the amount of radioactive lead.

What additional piece of information must Jenny have in order to determine the age of the zircon?

• the decay rates of radioactive uranium and lead

• the density of the rock in which the zircon was found

• the ages of any fossils found near her sample of zircon

• the thickness of sedimentary rock layers found near the zircon

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The diagram below represents a stack of rock layers. These layers have not changed position since they formed. Examine the diagram, and answer the question that follows.

If the age of layer 4 is 400 million years and the age of layer 1 is 500 million years, then the age of layer 3 is

• older than 500 million years.

• 500 million years.

• between 400 million and 500 million years.

• younger than 400 million years.

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