Geological Time and Fossils

Deep Time

Earth’s history spanning billions of years (~4.5–4.6 billion years)

Catastrophism

The idea that Earth’s features formed through sudden violent events

Uniformitarianism

The idea that present processes operated the same way in the past

Modern geological view

Both catastrophism and uniformitarianism shape Earth

Relative Dating

Determining the order of events without exact ages

Absolute Dating

Determining the numerical age of rocks using radioactive decay

Half-life

The time required for half of a radioactive isotope to decay

Radiometric Dating

Method of determining age using radioactive decay

Principle of Superposition

Oldest rock layers are at the bottom, youngest at the top

Original Horizontality

Sedimentary layers are originally deposited flat

Cross-cutting Relationships

A fault or intrusion is younger than the rock it cuts through

Lateral Continuity

Rock layers extend outward in all directions until they thin out

Inclusions

Rock fragments inside another rock are older than the host rock

Unconformity

A gap in the geologic record caused by erosion or non-deposition

Fossil Succession

Fossils appear in a predictable order through time

Geologic Timescale

A timeline of Earth’s history divided into eons, eras, and periods

Eon

Largest division of geologic time

Era

Subdivision of an eon

Period

Subdivision of an era

Archean Eon

Early Earth, first simple life forms appear

Proterozoic Eon

Oxygen builds up, first multicellular life appears

Paleozoic Era

Marine life dominates, first land plants and animals appear

Mesozoic Era

Age of dinosaurs

Cenozoic Era

Age of mammals and modern life

Mass Extinction

A rapid loss of many species in a short period of time

Permian Extinction

Largest mass extinction in Earth’s history

Cretaceous Extinction

Extinction event that wiped out dinosaurs

Fossil

Preserved remains or traces of ancient organisms

Body Fossil

Actual remains of an organism (bones, shells)

Trace Fossil

Evidence of organism activity (footprints, burrows)

Fossil Formation Process

Death, rapid burial, sediment buildup, mineral replacement

Sedimentary Rock

Type of rock where most fossils form

Why fossils are not in igneous rocks

Heat from magma destroys organic remains

Index Fossil

A fossil with a short lifespan and wide geographic distribution

Purpose of Index Fossils

Used to determine relative ages of rock layers

Fossil Record

Collection of all fossils showing evolution over time

Evolution

Change in species over time through natural selection

Natural Selection

Process where favorable traits increase survival and reproduction

Fossil Radiation

Rapid increase in diversity of organisms

Cambrian Explosion

A major fossil radiation event with rapid diversification of life

Burgess Shale

A fossil site in BC with early marine life from the Cambrian

Drumheller Fossil Site

Alberta location rich in dinosaur fossils

Alberta Fossil Law

Fossils belong to the province and require permits to excavate

Surface Fossil Collection

Restricted in parks but allowed on Crown land with permission