Question 1

Refer to the figure, which shows an imaginary name scheme for an undisturbed site with distinct fossil assemblages in the top five layers of strata.  Your research team is excited to find (through comparison with other sites around the globe) that these assemblages correspond to some of the known historical periods on Earth.Specifically, the "Leverett" assemblage contains only microscopic life forms, while the "Hadley" stratum contains diverse marine invertebrate animals but no evidence of terrestrial life.Based on this information, which eon in Earth's history contains the "Hadley" stratum?

Accepted Answer

The answer of Refer to the figure, which shows an...

Question 2

A pure radioactive substance has a mass of 30 micrograms but had a mass of 240 micrograms 48 years ago.Assuming that the only changes in mass are due to radioactive decay, the half-life of the substance is _______ years.

Accepted Answer

The half-life of a radioactive substance is the time it takes for half of the substance to decay. In this case, the substance has lost 240 - 30 = 210 micrograms of mass over a period of 48 years.

Using the formula for radioactive decay, we can find the number of half-lives that have occurred:

N = N0 (1/2)^(t/T)

Where N is the current mass, N0 is the original mass, t is the time elapsed, T is the half-life.

Plugging in the given values gives:

30 = 240 (1/2)^(48/T)

Simplifying:

1/8 = (1/2)^(48/T)

Taking the logarithm of both sides:

-3 = 48/T * log(1/2)

Solving for T:

T = 16 years.

Therefore, the answer is D.

Question 3

Which statement about igneous rocks is true?

Accepted Answer

Igneous rocks are formed from the solidification of magma or lava and are commonly used in radiometric dating because they contain isotopes with long half-lives.

Note: A is incorrect as igneous rocks are not formed from accumulation of grains in water. B is incorrect as they can be found in various locations, not just ancient oceans. D is incorrect as carbon-14 dating is only useful for dating organic material and not applicable to igneous rocks. E is incorrect as amber is a fossilized tree resin and not an igneous rock.

Question 4

The plates of Earth's crust collectively make up the

Accepted Answer

The lithosphere is the rigid, outermost layer of the Earth consisting of the crust and uppermost part of the mantle. It is broken into several large plates that move and interact with one another, causing tectonic activity such as earthquakes and volcanic eruptions. The other options are not correct: A) the asthenosphere is a soft, weak layer of the mantle beneath the lithosphere, B) a subduction zone is where one tectonic plate is forced beneath another as they converge, C) the tectonic zone is not a recognized term in geology, and E) the tension zone is also not a recognized term in geology.

Question 5

The half-life of a particular radioactive isotope of element X is 100 years.If you know that 500 years ago a fossil contained 10 mg of this isotope, you would expect to find about _______ mg in that fossil today.

Accepted Answer

The half-life of the isotope is 100 years, meaning the amount of the isotope halves every 100 years. In 500 years, this process would occur 5 times (500 years / 100 years per half-life = 5 half-lives). Starting with 10 mg, after 5 half-lives, the amount would be halved 5 times: 10 mg → 5 mg → 2.5 mg → 1.25 mg → 0.625 mg → 0.3125 mg, which is approximately 0.3 mg.

Question 6

What substance does carbon-14 decay into?

Accepted Answer

Carbon-14 undergoes beta decay to form nitrogen-14.

Question 7

Which statement about the Phanerozoic eon is false?

Accepted Answer

The statement that life was restricted to microscopic aquatic forms is false. While microscopic aquatic life certainly existed during the Phanerozoic eon, it was also a time of great diversification and evolution among plants and animals, including the appearance of complex organisms such as mammals and birds.

Question 8

In the upper atmosphere, the bombardment of neutrons with nitrogen-14 varies somewhat over time.If in the past this rate had been lower, objects dated by _______ dating would now appear _______ than they really are.

Accepted Answer

Carbon-14 dating is used to date objects up to about 50,000 years old. The rate of bombardment of neutrons with nitrogen-14 in the upper atmosphere has been relatively constant over the past 50,000 years. However, if this rate had been lower in the past, then there would have been less carbon-14 produced. This would mean that objects dated by carbon-14 dating would now appear older than they really are.

Question 9

A layer of rocks is known as

Accepted Answer

A layer of rocks is called a stratum. Sedimentary and igneous are types of rocks, while Steno and eon are not relevant to this term.

Question 10

Plankton, which are associated with fossil assemblages from the Proterozoic eon through the present day, are best described as

Accepted Answer

Plankton are defined as small floating organisms that are unable to swim against currents. They include both microscopic plants (phytoplankton) and animals (zooplankton) that drift in the ocean or other bodies of water. Plankton have been present in fossil assemblages for billions of years, from the Proterozoic eon to the present day.

Question 11

Earth was devoid of life during the _______ eon.

Accepted Answer

The Hadean eon (4.6 billion to 4 billion years ago) was a period of intense heat and frequent geological activity, with Earth's surface constantly bombarded by asteroids and comets. It is believed that this environment was unsuitable to support life, and thus Earth was devoid of life during this eon.

Question 12

Which of the following is the shortest period of time?

Accepted Answer

The half-life of ¹⁴C is 5,730 years, so two half-lives would be 11,460 years. This is the shortest period of time among the given options.

Question 13

The first prokaryotic organisms evolved during the _______ eon.

Accepted Answer

The Archaean eon is the oldest of the three eons in Earth's history and lasted from 4 to 2.5 billion years ago. It was during this time that the first prokaryotic organisms evolved, including bacteria and archaea. The other answer choices are not associated with the evolution of prokaryotic organisms.

Question 14

Fossils found in lower strata of undisturbed sedimentary rocks are _______ and _______ similar to modern-day organisms than those found in higher strata.

Accepted Answer

Fossils in lower strata are older due to the way sedimentary rocks form over time, with newer layers accumulating on top of older ones. These older fossils are generally less similar to modern-day organisms, reflecting the evolutionary changes that have occurred over time.

Question 15

Which group is documented in fossils from the Proterozoic eon?

Accepted Answer

Plankton, particularly microfossils like acritarchs, are documented in the Proterozoic eon.

Question 16

Which of the following could be most accurately dated using carbon-14 dating?

Accepted Answer

Carbon-14 dating is effective for dating organic materials up to about 50,000 years old. A fossil between 10,000 and 20,000 years old falls within this range.

Question 17

In undisturbed strata of sedimentary rock, the oldest rocks

Accepted Answer

In undisturbed strata of sedimentary rock, the oldest rocks are found at the bottom because they were deposited first and then covered by younger layers of sediment over time. This is known as the law of superposition. Therefore, choice B is the correct answer.

Question 18

A paleontologist discovers a stromatolite and suspects that its older layers may contain fossils more than 3 billion years old.Which method will likely produce the best estimate of its age?

Accepted Answer

Radiometric uranium-235 dating of nearby igneous rocks would provide the best estimate of the age of the stromatolite. This method measures the decay of uranium-235 into lead-207 and can be used to date the igneous rocks formed from volcanic activity that occurred around the time the stromatolite was formed. This would provide a more precise estimate of the age of the stromatolite's layers compared to other methods.

Question 19

Which of the following radioactive substances is commonly used to date very ancient (older than the Cenozoic) fossils and events in the history of life?

Accepted Answer

Potassium-40 is commonly used to date very ancient fossils and events in the history of life, as it has a much longer half-life compared to carbon-14. The decay of potassium-40 into argon-40 is used to determine the age of rocks and fossils older than the Cenozoic era, which is approximately 66 million years ago.

Question 20

Which statement about stratigraphy is false?

Accepted Answer

This statement is false because organisms found in younger strata are typically more similar to modern organisms than those found in older strata. This is because the organisms found in younger strata are closer in time to the present day and have had less time for evolutionary change.

Quiz 24: The History of Life on Earth