Exam 9: Deep Time: How Old Is Old

Concerning the relative ages of the marble and sandstone,

Two atoms of a single element that differ in number of neutrons are said to represent two distinct __________ of that element.

The beginning and end points of eras, epochs, and periods on the geologic time scale are set by __________ ages.

How is the half-life of a radioactive parent isotope defined?

In an undisturbed sequence of sedimentary rocks, younger layers overlie older layers, according to the principle of

It appears that the dates that early geologists identified as the boundaries between eras coincide with mass extinction events. What is a mass extinction event? What might this event look like in the fossil record?

Do the fossils preserved in the rock record accurately and completely represent the entire extent and biodiversity of life on Earth? What does it take to create and preserve a fossil?

If the relative ages of two formations are known, their __________ can be inferred.

The geologic time scale is broken into a series of eras, epochs, and periods based mainly on the fossils found in each section. This is an example of __________ dating.

Your friend the archaeologist, who studies the ancient human past, has asked you to find a numerical date for some hominid artifacts found buried by ash from a volcanic eruption. To do this, you can use carbon-14 dating, which has a half-life of 5,730 years, or uranium-238, which has a half-life of 4.5 billion years. Based on their half-lives, which isotopic dating system will give your friend the most accurate numerical age? Explain.

In the following image of the Grand Canyon, identify the disconformity.

Unconformities represent __________ in the rock record.

What is the principle of uniformitarianism? How does this principle apply to our understanding of the Earth system? How is this useful in the context of relative dating?

Place the layers and geologic events in order from oldest to youngest. Make sure to include all of the layers and events, including the top surface. (There will be one event/layer per line when complete.)

If a sandstone lies on top of a shale,

Relative ages expressed on the geologic time scale primarily resulted from the study of

In an unweathered sample of igneous rock, the ratio of an unstable isotope to its stable daughter isotope is 1:15. If no daughters were present at the time the rock cooled below closure temperature, and the half-life of the isotope is 50 million years, how old is the rock?

Which type of unconformity requires there to have been little to no deformation in the rocks before and after the unconformity was created?

The surfaces named contacts #2 and #3 in the following image are examples of

A __________ consists of a sequence of similar rocks that can be found across a region.