The History of the EarthThe evolution of the continents
The evolution of the continentsWe have a good idea of the history of the continents over the past600 million years.Based on:Paleomagnetic studies: positions of continents with respect to thepoles.Geological studies: similarities and differences of rocks on differentcontinents and interpretations of ancient depositional environments.Paleontological studies: similarities and differences of fossilorganisms on different continents.
Plate tectonics was ongoing through all of this time, bringingcontinents together to form mountain belts and tearing them apartto form ocean basins.Over all this time there were other changes taking place:Variation in O2 levels inthe atmosphere.
"Plate tectonic maps and Continental drift animations byC. R. Scotese,PALEOMAP Project (www.scotese.com)"Several continental reconstructions are used in the lecture slides butare not available here. These slides are available at:
Cambrian PeriodGondwanaland: asupercontinent made up ofSouthAmerica, Africa, Australia,Antarctica, India andportions of othercontinents.Located near the south pole.Extensive glaciers coveredmuch of Gondwanaland.Part of Nova Scotia wasAttached to Gondwanaland.
North America, Europe, Siberia and Asia were all separate.
The equator passedthrough North Americabut it was a barren landmass (no land plants yet).Sea level rose and felland much of the timeNorth America was anextensive subaeriallowland surrounded bya shallow marine shelfsetting.
Ordovician PeriodThe separate continentswere beginning to collidedue to plate movement.North America andEurope were comingtogether
Northern Appalachiansbegan to form due tocompressive force withplate convergence.A trench along thenorthwestern margin ofNorth America formed avolcanic island arccomplex.
Sea level rose andfell, repeatedly, over aland surface of low relief.Several smalldepositional basinsdeveloped where thecrust was subsiding.Most sedimentsdeposited in southernOntario were marinelimestones and shales.
Silurian PeriodNorth America andEurope joined (completingthe central and northernAppalachians) by the endof the Silurian.The Siberian/Asiancontinent was convergingon Europe.The North America/Europecontinent began toapproach Gondwanaland.
An extensive trench and volcanic arc developed along the east coastof North America.Taconialand was the growing mountain range that was forming dueto compressive forces associated with convergence of North Americaand Europe.
Southern Ontario received shales and sandstones that were erodedfrom the rising mountains.55% of the natural gas produced in Ontario comes from Siluriansandstones.
In later Silurian time mountain building diminished and limestoneswere deposited in southern Ontario.Rocks exposed along the Niagara Escarpment are all of Silurian age.Much of western Canada was covered by a shallow sea in whichlimestones were deposited.
Devonian PeriodContinued approach ofNorth America towardsGondwanaland.N. America, Europe, Asiaand Siberia were beginningto form a secondsupercontinent: Laurasia.
An extensive mountain belthad developed all along theeastern margin of NorthAmerica.Sea level was very high andmuch of North Americawas covered by a shallowsea.
Southern Ontario wascovered by a shallow sea inwhich limestones andevaporites (halite andgypsum) were depositedImportant economicdeposits for oil and gas, saltand gypsum.Extensive limestones andsalts were depositedthroughout westernCanada.
A large limestone reef complex extended over much of Alberta.These reef deposits areimportant sources of oil andgas today.Oceanic crust continued tosubduct along the west coastof North America (volcanicarc complex).
Carboniferous PeriodContinents continue to come together.African Gondwanalandcollided with North Americaforming the southernAppalachian Mountains.Much land mass nearequator: abundant landplants, increasedatmospheric O2.
Most of North America wascovered by shallow seas orswampy lowlands.Much of North America’scoal deposits were formed atthis time.
Permian PeriodAsia collides with Europeto form the UralMountains.One large supercontinent(called Pangea) forms withthe merging of Laurasiaand Gondwanaland.
Most of eastern North America was dry land, the west was a shallowsea.An outcome of the comingtogether of the largelandmass: extensiveweathering, removing CO2from the atmosphere.Loss of CO2 reduced globaltemperature.
Extensive volcanism in Siberia (related to collision): SiberianTraps, a flood of basaltic lava, 2 million cubic kilometres.This extensive volcanicactivity may have produceddust that further reducedthe Earth’s temperature.Lands were dry andcool, reducing plant coverand reducing O2 in theatmosphere.
Sea level was particularly low.Permian ended with the mostdramatic mass extinction inEarth history: up to 95percent of marine life died off.Pangea persisted and a secondmajor mass extinction marksthe end of the Triassic Period.
Jurassic PeriodPangea began to break upwith the rifting of NorthAmerica, drifting to thenorthwest.Atlantic Ocean began to open.Sea level began to rise andglobal temperaturescontinued to becomewarmer.Period of rapiddiversification of organismsand the dinosaurs becamethe dominant group.
The Rocky Mountainsbegan to rise up andshallow seas moved bothnorth and south acrossmuch of central NorthAmerica.
Cretaceous PeriodContinents continued tomove apart.The Rocky Mountainswent through a majorperiod of construction inthe Early Cretaceous.Small land masses on thesubducting Pacific Platecollided with NorthAmerica.
Extensive volcanism and intrusion took place all along the westernedge of North America.Volcanic ash beds severalcentimetres thick are foundthousands of kilometresfrom the volcanic sources(massive explosions).Sea level continued to rise tothe mid-Cretaceous and thenbegan to fall.
Central North Americaflooded by a sea extendingfrom the Arctic Ocean tothe Gulf of Mexico (WesternNorth American Seaway).Sandstones and shales wereshed off the risingmountains, into the seaway.Dinosaurs dominated untilthe end of the mass extinctionat the end of the Cretaceous.
Cenozoic EraNorth & SouthAmerica, Australia andAntarctica spread awayfrom Pangea, furtheropening the AtlanticOcean.Africa collided withEurope; India collidedwith Asia.The early Cenozoic wasanother period ofmountain building in theRocky Mountains (moresmall collisions).
Mammals diversified andbecame the dominantgroup of organisms.
4 Billion years from now………..The sun explodes, Earth is finished….