Relative age and fossils terms

Mesozoic Era

"Age of Reptiles" (245-144 million years ago); rise of mammals and dinosaurs; the rise of birds; extinction of dinosaurs, rise of flowering plants

Precambrian Eon

90% of Earth's history, unicellular life appears and exists only in the sea.

trace fossil

A type of fossil that provides evidence of the activities/behavior of ancient organisms

correlation in geology

By studying their fossil content, geologists can match rock layers that are far away from each other (and even in different parts of the world).

Body fossils

Hard parts of an organism, such as bone, teeth or shells, that has been preserved into a fossil. They tell us what the organism looked like.

unconformity

Missing rock layer. Could be from erosion or other geologic events.

deposition

Process in which sediment is laid down in new locations.

erosion

Processes by which rock, sand, and soil are broken down and carried away

relative age

age of layers in comparison to others

Intrusion (magma)

always younger than what it cuts through

fault

always younger than what it offsets

Cenozoic Era

era that began about 66 million years ago, known as the "Age of Mammals"

uniformitarianism

is the idea that the geologic processes that operate today also operated in the past and they are slow and steady.

Strata

layers of sedimentary rock

index fossil

occurs in many locations, lived short period of time, can be used to tell the age of a rock layer (without getting radiometric ages)

law of superposition

oldest at the bottom, youngest at top

law of horizontality

sedimentary rocks are originally deposited in horizontal layers

crosscutting relationships

states that an igneous intrusion (or fault) is always younger than the rock it cuts across.

Paleozoic Era

the part of geologic time 570-245 million years ago ; invertebrates, fishes, amphibians, reptiles, ferns, and cone-bearing trees were dominant. Life began to evolve from ocean to land.

absolute age

the real age of a rock layer calculated with radioactive decay

Stratigraphy

the study of rock layers and the sequence of events they reflect