Ch 18

Geologic Time Scale
 Law of superposition- youngest is on top oldest on bottom
 Geologic column- arrangement of rock layers

 Era- A very large unit of time
 Period-A division of an Era
 Epoch-A division of a Period

Section 18.1 review
True  Scientists use events such as major changes in the earth’s surface and climate and the extinction of various species as the basis for dividing the geologic time scale into units.

Section 18.1 review
True  Using the law of superposition and the study of index fossils, nineteenth century scientists determined the relative ages of rock layers
False  Eras are subdivisions of periods

Section 18.1 review
False
 Scientists can use the geologic column to estimate the relative ages of rock layers only if the rock contains radioactive minerals
True
 Fossils of mammals are common in Cenozoic rocks

Complete the statement
 Rock layers in the geologic column can be distinguished from one another according to
 The geologic era that followed
Precabrian time is called the

Complete the statement
 According to the geologic column in the diagram, the
 Based on late Precambrian fossils and other types of geological evidence, scientists theorize that life began

Last question in 18.1
 The era that is divided into

Theory of Evolution
 Organisms change over time.
New kinds of organisms are derived from ancestors.

Precambrian time
 Started 4.6billion years ago
 Ended 540million years ago
 Characteristics of this time:
 Soft-bodies or single cell organisms, Stromatolites
 Lots of volcanoes, mountain formation, sediment formation & metamorphism

Paleozoic Era
540-248 million years ago
 Periods:
 Cambrian
 Ordovician
 Silurian
 Devonian
 Carboniferous
 Permian

Paleozoic Era
540-248 million years ago
 Cambrian
 Advanced forms of marine life and first invertebrates appear
 Ordovician
 Brachiopods increase: trilobites decline: graptolites flourish: First vertebrates (fishes appear)

Paleozoic Era
540-248 million years ago
 Silurian
 First land plants and animals appear
 Devonian
 Age of fishes
 First amphibians
 Ferns and cone bearing plants

Paleozoic Era
540-248 million years ago
 Carboniferous
 Split into two epochs:
Mississippian and Pennsylvanian
 Amphibians flourish
 Giant cockroaches
 Permian
 Pangaea comes together mass extinctions

Mesozoic Era
248-65 million years ago
 Periods
 Triassic
 First Dinosaurs, tropical weather,
 Jurassic
 Large Dinosaurs, tropical weather,
 Cretaceous
 First flowering plants, mass extinction

Cenozoic Era
65 million years to today
 Periods
 Tertiary
 Paleocene
 Oilgocene
 Miocene
 Pliocene
 Quaternary
 Pleistocene
 Holocene

Cenozoic Era
65 million years to today
 Periods
 Tertiary
 Age of mammals
 Pangaea separates
 Quaternary

Ice age and human’s develop

18.2 review
The presence of cross-bedded sandstone may indicate that the region where it is present was once:
Precambrian
 Shields are large areas of exposed rock of what era?
forms of marine life
The fossil record indicates that which of the following thrived during the
Paleozoic Era

18.2 review
The Devonian period is also known as the Age of
Dinosaurs first appeared during the
During which era did glaciers cover nearly one third of the earth’s land area?

18.2 review
Pilocene  During which epoch did the first modern horses appear?
Silurian
 Which geologic period is missing from this diagram?
The Paleozoic Era
Cambrian  Ordovician  _________  Devonian

Time

18.2 review
Stromatolites  What are the most common
Precambrian fossils called?
Tertiary
 Which period of the Cenozoic
Era includes the time before the last major ice age