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