Exam 4: Geologic Time Concepts and Principles

Relative dating of geologic events was not possible before the discovery of radioactivity in the late 19th century.

List at least three pieces of information you would need when attempting to radiometrically date an igneous rock using uranium-238/lead-206 isotopes.

A rock sample containing an isotope with a half-life of 28 million years has an initial mass of 184 grams. How much parent isotope remains after 3 half-lives?

Some scientists have suggested that human intervention in the Earth system has been responsible for a new epoch of geologic time called the Anthropocene.

James Hutton is considered the founder of modern day geology.

The principle of superposition states that ____.

Describe and discuss the methods for deriving absolute geologic dates. How have these methods influenced the geologic time scale? Discuss possible sources of uncertainty in dates determined using these methods.

The most accurate radiometric dates are obtained from ____________________ rocks.

Explain how John Wesley Powell could have used the relative dating principles of original horizontality, superposition, and lateral continuity on his journey through the Grand Canyon.

All atoms of the same element have the same atomic number.

If sedimentary rocks are tilted steeply, we assume that they were initially deposited ____________________.

Protons are neutral particles in the nucleus of an atom.

Relative dating approximates how long ago a particular event took place .

Uniformitarianism is the assumption that ____.

Discuss the recent proposal by Paul Crutzen and Eugene Stoermer for the addition of the Anthropocene Epoch to the Geologic Time Scale. What evidence supports this inclusion? What refutes it?

Geologists use the natural radioactive decay of elements as the foundation for relative time dating.

The principle of lateral continuity states that sedimentary beds are deposited horizontally with the oldest beds on the bottom.

List three ways in which scientists can detect changes in climate, particularly due to the accumulation of carbon dioxide, by examining the geologic record.

The principle of _________________________ states that an igneous intrusion or a fault must be younger than the rock it intrudes or displaces.

Early geologists tried calculating the age of Earth based on sedimentation rates and deduced ages of 1 million to 2 billion years old. Explain the logic behind using sedimentation rates to calculate the age of Earth, and explain at least two reasons why this method did not work.