|
Era or Eon
|
Period
(years ago)
|
Activity Affecting Pennsylvania
|
Main PA deposits
|
Dominant Life in PA
|
|
Cenozoic Era
(Recent Life)
|
Quaternary
(0 to 2 million)
|
Glaciation; periglacial erosion and
deposition
|
Sand, silt, clay, gravel
|
Mammals, including humans
|
|
Tertiary
(2 to 67 million)
|
Weathering and erosion.
Creation of present landscape
|
Sand, silt, gravel
|
Mammals, grasses
|
|
Mesozoic Era
(Middle Life)
|
Cretaceous
(67 - 140 million)
|
Erosion and weathering
|
Clay, Sand
|
Dinosaurs, mammals, birds
|
|
Jurassic
(140 - 208 million)
|
Diabase intrusions; opening of
Atlantic Ocean
|
Diabase
|
Dinosaurs, mammals, birds
|
|
Triassic
(208-250 million)
|
Separation of North America from
Africa; sedimentation in rift valley
|
Shale, sandstone, diabase
|
Dinosaurs, early mammals and birds
|
|
Paleozoic Era
|
Permian
(250-290 million)
|
Allehanian Orogeny: Collision of Africa and North America; mountain building,
thrust faulting and folding; much erosion
|
Sandstone, shale
|
Insects, amphibians, reptiles
|
|
Pennsylvanian and Mississippian
(Carboniferous)
(290-365 million)
|
Alluvial deposition; eastward advance
of shoreline followed by development of low, flat alluvial plain
|
Sandstone, siltstone, shale, coal,
limestone
|
Trees, ferns, amphibians,
air-breathing mollusks, insects
|
|
Devonian
(365-405 million)
|
Acadian Orogeny; Collision of
Avalonia, Europe, and North America; formation of Catskill Delta
|
Conglomerate, sandstone, shale
|
Fish, amphibians, insects, land
plants
|
|
Silurian
(405-430 million)
|
Erosion of mountains; deposition of
sand and mud
|
Conglomerate, sandstone, limestone
|
Corals, fish
|
|
Ordovician
(430-500 million)
|
Taconic Orogeny: Thrusting of volcanic arc; development of Appalachian basin
|
Shale, limestone, dolomite
|
Mollusks, bryozoans, graptolites
|
|
Cambrian
(500-570 million)
|
Transgression of the sea' carbonate
deposition
|
Limestone, dolomite, quartzite
|
Trilobites, brachiopods
|
|
Proterozoic Eon
|
(570 million-2.5 billion)
|
Accretion of microplates to form
Laurentia
|
Schist, slate, marble
|
Blue-green algae, jellyfish, worms
|
|
Archean Eon
|
(2.5-3.8 billion)
|
Bombardment by meteorites; creation
of continental crust
|
None identified
|
Bacteria
|
|
Pre-Archean Eon
|
(3.8-4.5 billion)
|
Formation of Earth and solar system
|
None identified
|
None identified
|
| |
