Question 1

The stratigraphic order of the fossils from animal species is known as the

Accepted Answer

Faunal succession is the concept that sedimentary rock layers contain a vertical sequence of fossils that are recognizable and distinct across different geographic locations, reflecting a historical sequence of biological evolution and extinction events. This principle is fundamental in the study of stratigraphy and paleontology.

Question 2

Which of the following statements regarding radiometric dating is true?

Accepted Answer

Carbon-14 dating is effective for materials up to about 50,000 to 60,000 years old. Beyond this, there's too little C-14 left to accurately measure, making the method unreliable for materials over 100,000 years old.

Question 3

Which of the following statements about radioactivity is false?

Accepted Answer

Energy is not consumed during radioactive decay; instead, energy is released. This release of energy is a fundamental aspect of radioactive decay processes, as unstable nuclei release energy to become more stable.

Question 4

A rock formed with 1000 atoms of a radioactive parent element,but contains only 250 radioactive parent atoms today.If the half-life for the radioactive element is one million years,how old is the rock?

Accepted Answer

The rock is 2 million years old. This is because the half-life of the radioactive element is one million years, meaning every million years, the amount of the radioactive parent element is reduced by half. Starting with 1000 atoms, after one million years, it would reduce to 500 atoms (first half-life), and after another million years, it would reduce to 250 atoms (second half-life). Thus, it takes 2 million years to go from 1000 atoms to 250 atoms.

Question 5

Human beings (homo sapiens)evolved during which geologic era?

Accepted Answer

Human beings (Homo sapiens) evolved during the Cenozoic era, which is the current and most recent of the three major subdivisions of animal life geologic time, covering the period from 66 million years ago to the present.

Question 6

Which of the following materials might be dated using carbon-14?

Accepted Answer

Carbon-14 dating is a technique used to determine the age of organic materials. Wood is an organic material, so it can be dated using carbon-14.

Question 7

Almost nine-tenths of Earth's history occurs during the

Accepted Answer

The Precambrian encompasses nearly 88% of Earth's history, starting from the formation of the Earth about 4.6 billion years ago and ending with the start of the Cambrian Period about 541 million years ago. It includes both the Archean and Proterozoic eons, covering a vast span of time before the Phanerozoic eon, which includes the Paleozoic, Mesozoic, and Cenozoic eras.

Question 8

Which of the following radioactive isotopes is the most useful for dating very young (<10,000 years old)wood and charcoal?

Accepted Answer

Carbon-14 is the most useful isotope for dating very young (less than 10,000 years old) wood and charcoal because it has a relatively short half-life of about 5,730 years, making it ideal for measuring ages in this range.

Question 9

The absolute age of a geologic event in the rock record is

Accepted Answer

The absolute age of a geologic event is determined by calculating the number of years that have passed between the event itself and the present day, using techniques such as radiometric dating.

Question 10

Which of the following instruments is used to precisely measure isotopes for radiometric dating?

Accepted Answer

A mass spectrometer is used to precisely measure the isotopic composition of elements, which is essential for radiometric dating techniques.

Question 11

What is the youngest rock formation exposed in the Grand Canyon?

Accepted Answer

The Kaibab limestone is the youngest rock formation exposed at the Grand Canyon, forming the uppermost layer of the canyon's rim.

Question 12

Which of the following radioactive isotopes has the shortest half-life?

Accepted Answer

Carbon-14 has a half-life of about 5,730 years, which is significantly shorter than the half-lives of potassium-40 (about 1.25 billion years), rubidium-87 (about 49 billion years), and uranium-238 (about 4.5 billion years).

Question 13

If Earth's history was compressed into a single calendar year,complex organisms (including those with shells)first appeared in

Accepted Answer

Complex organisms, including those with shells, first appeared around 541 million years ago during the Cambrian Explosion, which would be in October if Earth's history were compressed into a single calendar year.

Question 14

Radiometric dating is possible if a rock contains a measurable amount of

Accepted Answer

Radiometric dating relies on the decay of unstable parent atoms into stable daughter atoms over time. Measuring the ratio of parent to daughter atoms in a rock allows scientists to determine its age. Therefore, a rock must contain both types of atoms for radiometric dating to be possible.

Question 15

When did the oldest rocks,now exposed at the base of the Grand Canyon,form?

Accepted Answer

The oldest rocks now exposed at the base of the Grand Canyon formed during the Precambrian era, which is the earliest part of Earth's history, before the Paleozoic era.

Question 16

Radiometric dating is least useful for dating __________ rocks.

Accepted Answer

Radiometric dating is least useful for dating sedimentary rocks because they are formed from the accumulation of small pieces of older rocks and do not contain minerals that crystallize from molten material, making it difficult to determine their exact formation age.

Question 17

Which of the following can change the rate of radioactive decay?

Accepted Answer

The rate of radioactive decay is a constant for a given isotope and is not affected by external factors such as temperature, pressure, or chemical reactions. It is a fundamental property of the nucleus of the atom.

Question 18

Which of the following statements is false?

Accepted Answer

Dikes are younger than the rocks they cross-cut because they intrude into pre-existing structures. This principle is part of the basic geological principle of cross-cutting relationships, which states that any geological feature that cuts across another is the younger of the two features.

Question 19

Approximately how fast do plates spread apart?

Accepted Answer

Tectonic plates spread apart at rates of about 2 to 20 centimeters per year, which is consistent with observations of plate movements at mid-ocean ridges and other tectonic boundaries.

Question 20

When did the horizontal,layered sedimentary rocks in the Grand Canyon form?

Accepted Answer

The horizontal, layered sedimentary rocks in the Grand Canyon primarily formed during the Paleozoic era, which spans from about 541 to 252 million years ago. This era is known for the development and diversification of early life forms, including the formation of extensive marine and terrestrial sedimentary rock layers.

Quiz 8: Clocks in Rocks: Timing the Geologic Period