Unit 2: Geologic Time Vocabulary

EES Unit 2 Essential Vocabulary

What is absolute time in geology?

Absolute time, or chronometric time, refers to specific intervals or moments measured in days, months, years, etc.

What is carbon dating?

The determination of the age of organic matter based on the relative proportions of carbon isotopes carbon-12 and carbon-14.

What marks the beginning of the Cenozoic Era?

The Cenozoic Era began about 66 million years ago and includes the first appearance of Homo sapiens.

Define continental drift.

Continental drift is the gradual movement of the continents across the Earth's surface through geological time.

What do cross-cutting relationships establish in geology?

Cross-cutting relationships establish that the geologic feature that cuts across another is always younger.

What is a daughter isotope?

A daughter isotope is the stable, non-radioactive isotope that is the final product of radioactive decay.

What is the largest subdivision in the geologic timescale?

The eon is the longest subdivision in the geologic timescale.

What distinguishes an era in geological time?

An era is a second-longest division of geologic time, based on major worldwide changes in types of fossils.

What is the definition of an epoch?

An epoch is the shortest subdivision of the geologic time scale and is a further subdivision of periods.

What causes extinction?

Extinction occurs when a species is diminished due to environmental forces like habitat fragmentation, global changes, or overexploitation.

Define fossil in geological terms.

A fossil is a preserved remnant or impression of an organism that lived in the past.

What is the geologic time scale?

The geologic time scale divides Earth's history into time units based on types of life-forms that existed during specific time frames.

What is a half-life?

Half-life is the time taken for the radioactivity of a specified isotope to fall to half its original value.

What does the inclusion principle state?

The inclusion principle states that rock fragments within another rock mass must be older than the rock mass containing them.

Define an index fossil.

An index fossil is used to establish the age of a rock layer as it was distinct, abundant, and existed for only a short span of geologic time.

What does the law of superposition state?

The law of superposition states that in horizontal layers of sedimentary rock, each layer is older than the layer above and younger than the layer below.

What is mass extinction?

Mass extinction is a significant loss of about three-quarters of all species in existence across the Earth over a short geological period.

What characterizes the Mesozoic Era?

The Mesozoic Era is characterized by the breakup of Pangaea and the dominance of dinosaurs and reptiles.

What is natural selection?

Natural selection is the process where organisms suited to their environment are better able to survive and reproduce.

Who is a paleontologist?

A paleontologist is a scientist who studies fossils to learn about past organisms.

What defined the Paleozoic Era?

The Paleozoic Era started about 544 million years ago and ended with mass extinctions around 245 million years ago.

What is Pangaea?

Pangaea was a supercontinent that contained all the world's land masses as they existed during the Permian and Triassic Periods.

Define period in geological time.

A period is the third-longest division of geologic time, characterized by types of life that existed and is subdivided into epochs.

What is a petrified fossil?

A petrified fossil is formed when minerals replace all or part of an organism.

What characterizes Precambrian time?

Precambrian time is the longest part of Earth's history, lasting from 4.0 billion to about 544 million years ago.

What does the principle of original horizontality state?

The principle of original horizontality states that layers of sediment are originally deposited in horizontal layers.

What is radiometric dating?

Radiometric dating is a technique used to calculate the absolute age of rocks and minerals by measuring the ratio of a radioactive isotope to its decay product.

What is radioactive decay?

Radioactive decay is the breakdown of a radioactive element, releasing particles and energy.

How is relative time determined?

Relative time is determined by organizing events in a chronological order based on their occurrence.

What are rock strata?

Rock strata are distinct, horizontal layers or beds of sedimentary rock formed over time by the accumulation of sediments.

What is a scientific theory?

A scientific theory is a well-tested concept that explains a wide range of observations.

What are trace fossils?

Trace fossils are indirect evidence of life preserved as impressions in rocks, such as trails, footprints, or burrows.

What is an unconformity in geology?

An unconformity refers to gaps in the geologic record indicating episodes of crustal deformation, erosion, and sea level variations.

How do rock strata help in determining relative time?

Rock strata help determine relative time through principles like superposition and original horizontality, which establish the chronological order of events based on the layering of rocks.

What are the fundamental principles of relative dating in geology?

The fundamental principles include the law of superposition, principle of original horizontality, principle of cross-cutting relationships, and principle of inclusions.

What are the three main types of unconformities?

The three main types of unconformities are angular unconformity, disconformity, and nonconformity.

Describe an angular unconformity.

An angular unconformity is a type of unconformity where younger sedimentary layers are deposited horizontally on top of older, tilted or folded sedimentary layers that have been eroded.

What is a disconformity?

A disconformity is an unconformity between parallel sedimentary layers, indicating a period of erosion or non-deposition without significant tilting or folding.

Explain a nonconformity.

A nonconformity is an unconformity where younger sedimentary rocks lie directly on top of older igneous or metamorphic rocks that have been eroded.