Transcript Exploring Geologic Time

Exploring
Geologic Time
The 4.6 billion years of Earth’s
history can be divided into 2
major time segments called
eons.
Precambrian
Phanerozoic
4600 Ma to 570 Ma
570 Ma to present
Ma means million of years ago
Precambrian Eon
 85% of Earth’s history
 intense volcanic activity; oceans form; meteorite
bombardment
 atmosphere develops from primitive through outgases from volcanoes to one with free oxygen (and
ozone layer)
 life begins with unicellular organisms (blue-green
algae and bacteria) and evolves to multi-cell
organisms like worms
 few fossils exist because most did not have hard
parts
The Phanerozoic Eon is divided
into time segments called eras.
Paleozoic
Mesozoic
Cenozoic
570 Ma to 245 Ma
245 Ma to 66.4 Ma
66.4 Ma to present
The Paleozoic Era
 most significant breakup period for first
supercontinent with development of smaller
continents and finally formation of Pangaea
 sea level rises and falls covering and uncovering the
new continents
 six periods are marked by significant differences in
lifeforms
 appearance of fish, insects, amphibians, and some
reptiles
The Mezozoic Era
known as age of reptiles; dinosaurs are
prominent lifeforms
last part of this period (Cretaceous) witnesses
large-scale extinction of marine and flying
reptiles as well as dinosaurs; extinction may
be due to massive asteroid collision with Earth
Pangaea breaks up
The Cenozoic Era
age of mammals
climates cool generating widespread glaciation
humans evolve
high level of tectonic activity as plates
separate and evolve
Each era can be subdivided
into periods. Periods can be
subdivided into epochs. Each
time segment is characterized
by changes in landforms
(tectonics changes), climate,
and in life forms.
Here is an example of a
geologic timeline with
important events noted.
http://3dparks.wr.usgs.gov/co
loradoplateau/timescale.htm
Another site that provides
information about
characteristics and events in
various geologic periods:
http://geomaps.wr.usgs.gov/pa
rks/gtime/gtime2.html
Information about rocks of a
particular geologic time can be
displayed on a map called a
geologic map.
The most striking features of geologic maps are its
colors. Each color represents a different geologic
unit. A geologic unit is a volume of a certain kind of
rock of a given age range. So a sandstone of one age
might be colored bright orange, while a
sandstone of a different age
might be colored pale brown.
Many geologic units are given
names that relate to where
their characteristics are best
displayed, or where they
were first studied.
http://ncgmp.usgs.gov/ncgmpgeomaps
Here is a site to access
geologic maps of Maryland:
http://www.mgs.md.gov/esic/geo/