MLES Relative Age Date and Geologic Time

evolution events

Events where many different species come into existence and/or change over generations

mass extinction events

events that killed off the majority of living organisms at the time

Eons

the largest divisions of geologic time

Era

These are the smaller time divisions of Eons.

Period

These are the smaller time divisions of Eras.

Epoch

These are the smaller time divisions of Periods.

Geologic Time Scale

Divides Earth's history into intervals based on major events (evolution, extinction…)

Precambrian Time

The earliest and largest amount of time in Earth's history.

Paleozoic Era

Characterized by the evolution of single-celled organisms into more complex organisms (541-252 million years ago)

Mesozoic Era

"The Age of Reptiles" because the dinosaurs lived and went extinct during this era.

Cenozoic Era

"The Age of Mammals" and is the era in which we are living now.

Relative Age

What happened 1st, 2nd, 3rd…

Supercontinents

When all of Earth's landmasses came together into one massive continent.

Strata

layers of rock, usually sedimentary rock

Principle of Uniformitarianism

'The Present is the Key to the Past' -what happens on Earth today also happened in the Earth's past.

Law of Original Horizontality

Rock strata are formed in flat (horizontal layers).

Law of Superposition

The rock strata on the bottom are older than the rock strata on top.

The Law of Crosscutting Relationships

The geologic feature that cuts through rock strata is younger than the rock strata

Unconformity

A discrepancy in the relative age of the rock strata (layers that are NOT 1st, 2nd, 3rd…)

Disconformity

Missing rock strata that were eroded away by rain, wind, snow…

Angular Unconformity

Folded rock strata that touch horizontal rock strata

Nonconformity

Volcanic or metamorphic rocks that touch sedimentary rocks (these rocks do not form together and should not touch each other)