exploring geologic time. the 4.6 billion years of earth’s history can be divided into 2 major time...
TRANSCRIPT
Exploring Geologic Time
The 4.6 billion years of Earth’s history can be
divided into 2 major time segments called eons.
Precambrian 4600 Ma to 570 MaPhanerozoic 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
out-gases 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 570 Ma to 245 MaMesozoic 245 Ma to 66.4 MaCenozoic 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 Eraknown as age of reptiles; dinosaurs are
prominent lifeformslast 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 Eraage of mammalsclimates cool generating widespread
glaciationhumans evolvehigh 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/coloradoplateau/timescale.htm
Another site that provides information about
characteristics and events in various geologic periods:
http://geomaps.wr.usgs.gov/parks/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 agemight be colored pale brown. Many geologic units are givennames 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/