Geologic Time

\_____ record geologic and evolutionary changes throughout Earth's history.

Rocks

\_____- dates that specify the number of years that have passed since an event occured

Numerical dates

\_____- dates that place rocks in a sequence of formation

Relative dates

What principle applies to surface features like lava flows and beds of ash?

Principle of Superposition

In an undeformed sequence of sedimentary rocks, each bed is ____ than the one above and ____ than the one below. What principle is this?

older; younger; principle of superposition

What principle has layers of sediment that are generally deposited in a horizontal position?

Principle of Original Horizontality

What principle has beds that originate as continuous layers that extend in all directions until they eventually thin out or grade into a different sediment type?

Principle of Lateral Continuity

What is the principle where younger features cut across older features?

Principle of Cross-Cutting Relationships

\____- are fragments of one rock unit that are enclosed within another rock unit; the rock containing this is younger

inclusions

Layers of rock that have been deposited without interruption are called \_______.

conformable layers

\_____- is a break in the rock record produced by non deposition and erosion of rock units

unconformity

What are the three basic types of unconformities?

angular, nonconformity, disconformity

\_____- tilted rocks are overlain by flat-lying rocks

angular unconformity

\_____- sedimentary strata on either side of the unconformity are parallel

disconformity

\_____- sedimentary strata overlay metamorphic or igneous rocks

nonconformity

Where can all three types of unconformities be seen?

The Grand Canyon

\_____- are traces or remains of prehistoric life preserved in rock

fossils

\_____- is the study of fossils

Paleontology

Knowing the nature of life that existed at a particular time helps researchers understand past environmental conditions. T/F

True

\_____- mineral-rich groundwater flows through porous tissue and precipitates minerals

permineralization

\_____- is created when a shell is buried and then dissolved by underground water

mold

\_____- is created when the hollow spaces of a mold are filled

cast

\_____- happens when an organism is buried, followed by compression, which squeezes out gases and liquids leaving a thin film of carbon

carbonization

\_____- things that remain in the rock with the carbon film is lost

impressions

\_____- is the hardened resin of ancient trees; preserves insects very effectively

amber

\_____- fossil with indirect evidence of prehistoric life

trace fossils

Rapid burial and the possession of hard parts \_____ the chances of preservation as a fossil.

increases

\_____- involves matching of rocks of similar ages from different regions; provides a more comprehensive view of the rock record

correlation

Correlation within limited areas is often accomplished by noting the position of the bed in a sequence of \_____.

strata

What principle of fossil succession states that fossils are arranged according to their age?

Principle of Fossil Succession

\_____- is a group of fossils used to determine a rock's age

fossil assemblage

The nucleus contains \_______.

protons and neutrons

The atomic number is the number of \___ in the nucleus.

protons

The mass number is the number of \______ in a nucleus.

protons and neutrons

Isotopes have the same number of \_____ and a different numbers of \______.

protons; neutrons

\_____- is the spontaneous decay in the structure of an atom's nucleus

radioactivity

What are the three types of radioactive decay?

Alpha Emission, Beta Emission, Electron Capture

\_____- an alpha particle (two protons and two neutrons) are ejected from the atom; mass number is reduced by 4, and the atomic number is lowered by 2

alpha emission

\_____- a beta particle (an electron) is ejected from the atom; when ejected the mass number remains unchanged and the atomic number is increased by 1

beta emission

\_____- an electron is captured in the nucleus; the mass number remains unchanged and the atomic number is decreased by 1

electron capture

\_____- uses the decay of isotopes in rocks to calculate the age of that rock

radiometric dating

\_____- is the amount of time required for half of the radioactive isotope to decay

half-life

As the parent atoms decrease, the daughter atoms increase. T/F

True

Several naturally occurring radioactive isotopes are useful for \_________.

dating rocks

\_____- uses the radioactive isotope carbon-14 to date geologically recent events

radiocarbon dating

The half-life of carbon-14 is \______.

5,730 years.

\_________ is produced in the upper atmosphere from cosmic-ray bombardment.

Carbon-14

What does the geologic time scale encompass for all of Earth's history?

subdivides geologic history into units, originally created using relative dates

The Phanerozoic eon is divided into three eras:

Paleozoic ("ancient life"), Mesozoic ("middle life"), and Cenozoic ("recent life")

How many periods do the Paleozoic, Mesozoic and Cenozoic era's have?

Paleozoic (7), Mesozoic (3), Cenozoic (3)

Each period is divided into \_____.

epochs

Most detail in the geologic time scales is in the \_____.

Phanerozoic eon

What period does the first abundant fossil evidence appear at?

Cambrian period

Many Precambrian rocks are lightly deformed metamorphic rocks. T/F

False. Many Precambrian rocks are highly deformed metamorphic rocks.

\_____- refers to the earliest interval of Earth's history

Hadean

The geologic timescale is continuously updated. T/F

True.

\________ rocks can rarely be dated directly by radiometric means.

Sedimentary