Changes to Earth's Surface: Fossils and the Geologic Time Scale

Vocabulary practice flashcards covering fossil formation methods, fossil types, index fossils, and the divisions of the Geologic Time Scale from the lecture notes.

Fossil

Any naturally preserved evidence of life.

Permineralization

A fossilization process by mineral replacement where minerals fill in the pores of an organism's tissues.

Petrification

A fossilization process by mineral replacement occurring when an organism's tissues are completely replaced by minerals.

Trace fossils

Preserved evidence of an organism's activity rather than its physical body, including tracks, burrows, shelters, or coprolites.

Coprolites

Preserved fossilized animal dung, also known as "dung stone."

Mold

A cavity in rock where a plant or animal was buried and subsequently decayed or dissolved.

Cast

A fossil formed when sediment fills a mold cavity and hardens into rock.

Index fossils

Fossils of organisms that lived during a relatively short, well-defined time span, used by geologists to date the surrounding rock layer.

Phacops

An index fossil that indicates the surrounding rock layer is about $400$ million years old.

Tropites

An index fossil that indicates the surrounding rock layer is between $230$ and $208$ million years old.

Geologic Time Scale

A system that divides Earth's history into distinct intervals of time based on major changes in life-forms, climate, and rock types.

Eon

The largest division of geologic time; the four eons are Phanerozoic, Proterozoic, Archean, and Hadean.

Era

The second largest division of geologic time, which is subdivided into periods.

Period

The third largest division of geologic time, some of which are further divided into epochs.

Epoch

The fourth division of geologic time, representing subdivisions of geologic periods.

Paleozoic Era

The era meaning "old life" or "Age of Fishes," spanning from $540$ to $249$ million years ago, characterized by no land organisms (only fish, plants, and amphibians) and ending with a mass extinction.

Mesozoic Era

The era meaning "middle life" or "Age of Reptiles," lasting from about $249$ to $65$ million years ago, during which birds and small mammals appeared, and $50\%$ of all species went extinct by its end.

Cenozoic Era

The era meaning "recent life" or "Age of Mammals," lasting from about $65$ million years ago until the present day, containing early mammals that are now extinct, such as woolly mammoths.