Exam 24: Geologic Time

The time before the Phanerozoic eon is collectively called ______________ time.

The term Cambrian explosion refers to

The ______________ states that an igneous rock is younger than the rock layers it has disturbed.

The largest units of geologic time are the

Geologists have principally used which class of rocks to establish the relative time scale?

The actual age of rock layers and geologic events is referred to as ______________ geologic time.

The Paleozoic era ended with an event called the

______________ dating is used specifically to establish the absolute age of organic remains.

The span of time required for the radioactive decay of half the parent nuclei in a sample is known as the ______________.

The Pleistocene epoch is also referred to as the ______________.

The Mesozoic era began about how many million years ago?

Which of the following is the era sometimes called the age of reptiles?

Geology's best tool for establishing absolute geologic time is

A group of eras are called a(n)

The ______________ states that in a sequence of undisturbed sedimentary rocks, lavas, or ash, each layer is younger than the layer beneath it.

The Petrified National Forest is found in the state of ______________.

The Paleozoic era ended and the Mesozoic era began about ______________ million years ago.

The term age of reptiles is sometimes used to refer to the ______________ era.

Naturally occurring uranium ultimately decays to isotopes of the element named ______________.

Eras are divided first into smaller time units called ______________.