Relative Dating - Environmental Geology

Relative Time

The method of dating geological events by placing them in a sequential order.

Absolute Time

The method of determining the actual age of rocks or fossils through dating techniques.

Geologic Time

The timeline of Earth's history, spanning billions of years.

Unconformity

A surface of contact between two groups of unconformable strata, representing a period of erosion or non-deposition.

Steno's Laws

Principles that govern the relative dating of sediment layers, including superposition, original horizontality, and cross-cutting relationships.

Varves

Annual layers in sediments that alternate in color and composition, typically found in glacial lake deposits.

Faunal/Floral Succession

The principle that sedimentary rock strata contain fossilized flora and fauna that follow a recognizable chronological order, allowing for correlation of rocks in different areas.

Eon

The largest division of geological time, spanning hundreds of millions to billions of years.

Era

A subdivision of an eon, encompassing significant events in Earth's history.

Proterozoic Eon

The geological time period beginning around 2500 million years ago, following the Archean Eon.

Phanerozoic Eon

The geological eon that began around 542 million years ago, characterized by the presence of abundant fossil evidence.

Paleozoic Era

The era of geological time from about 542 to 252 million years ago, known for the emergence of complex life forms.

Mesozoic Era

The era of geological time from about 252 to 66 million years ago, known as the age of reptiles.

Cenozoic Era

The current era in geological time, starting around 66 million years ago, characterized by the dominance of mammals.

Superposition

The principle that in an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom.

Cross-Cutting Relationships

The principle that a geologic feature that cuts across another is younger than the feature it cuts.

How old do Geologists think the Earth is?

approximately 4.5 billion years