Unit 4.3 Relative Dating

Igneous

a type of rock that forms from the cooling of molten rock at or below the surface

Disconformity

a type of unconformity in which the sedimentary layers above and below the unconformity are parallel

Index fossil

fossils of widely distributed organisms that lived only during a short geologic period that can be used to date and correlate the rock strata

Deposition

the process in which material such as sediments is laid down

Biodiversity

the variety of life in the world or in a particular habitat or ecosystem; Early rock record has very little, but the increase in variety is visible on the rock record over time

radiocarbon dating (carbon-14 dating)

type of radiometric dating that can be used to date organic material up to 50,000 years old

Unconformities

A break or gap in the geologic rock record created when rock layers are eroded or when sediment is not deposited for a long period of time; it represents a missing segment of Earth's history

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes: present is the key to the past.

Biozone

A section of strata containing fossils characteristic to a specific geologic time frame

Metamorphic

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

Sedimentary

A type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together

Nonconformity

An type of unconformity in which older,eroded metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.

Folds (in rock layers)

Bending or buckling ofthe rock layers caused by movement in the Earth's crust.

fossil succession

Change in fossils/fossil distribution in the rock record over time; Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.

Biostratigraphy

Field of geology that uses biozones to study and date rock units based on the fossils present

Dike

Formed when magma forces itself vertically in rock layers

Sill

Formed when magma squeezes between horizontal layers of rock

Fault

Fracture in a rock (layer) along which movement has occurred.

Intrusion

Mass of igneous rock formed as magma is forced into or between other rocks and then solidifies.

Absolute dating

Method of measuring the age in years of a fossil, rock, feature, or a geologic event based on radiometric decay rates

relative dating

Method which places geologic events, rock layers, and fossils in chronological order; not exact age

Tilting (of rock layers)

Occurs when rock layers are uplifted unevenly, especially on one end, and are no longer horizontal

Principle (Law) of Cross-cutting relationships

States that any geologic feature that cuts partially though or completely across another feature is the younger of the two features.

Principle (Law) of Inclusions

States that any rock that is enveloped, or completely enclosed by another rock must be older than the rock that surrounds it.

Principle (Law) of Superposition

States that in undisturbed sequence of sedimentary strata, the oldest rock layer will be at the bottom and the youngest will be a t the top. This is the basis for all relative dating and is the fundamental concept in studying Earth's history.

Principle (Law) of Lateral Continuity

States that rock formations that have been subdivided since their original formation are continuous with each other.

Principle (Law) of Original Horizontality

States that sedimentary rock formations were first formed in horizontal layers.

Solidification

The change of state from a liquid to a solid; magma changing to rock

Weathering

The chemical and physical processes that break down rock at Earth's surface.

Catastrophism

The principle that states that changes in the earth's crust during geological history have resulted chiefly from sudden violent and unusual events.

Erosion

The process by which wind, water, ice, or gravity transports soil and sediment from one location to another

Uranium dating

Type of radiometric dating used to date rocks and fossils older than 50,000 years in age.

Angular Unconformity

Type of unconformity; Erosional surface in which the sedimentary rock layers below the surface are folded, uplifted, or tilted and then a younger horizontal layer is deposited on top.