Evolution of the continents Dr. William Kelly New York State Geological Survey New York State Museum Teachers Workshop On Evolution February 6, 2009

Continents – large blocks of low-density rock permanently removed from crustal recycling process Oldest rocks ~ 4.28 Ga (?) oldest mineral ~ Ga in rocks 3.8Ga Initial rapid growth (several hundred million years) followed by comparative stability Survive, move around earth without destruction metamorphosed – certainly torn apart – certainly but not destroyed! Today..... but not always Continent crust – 2.7 SG Ocean crust – 3.0 Mantle to 4.1 Outer core – 9.9 Inner core – 12.7 Solar system – 4.567Ga Earth – 4.56Ga (4.55+/-0.07Ga) Theia collision – 4.533Ga Earth solid crust – 4.433Ga Nuvvuagittuq gneiss – 4.28Ga Acasta gneiss – 4.03Ga Nuvvuagittuq gneiss

How do we know? Paleomagnetics tells us where Climate as indicated by rocks tells us where Radiometric dating tells us when

How do we know? Mountain belts tell us what’s next to what Sea floor spreading tells it all (last 200 my)

Ancient continents: Ur ~3.0 Ga Arctica ~2.5 Ga Atlantica ~ 2.0 Ga Baltica ~2.0 Ga Nena ~1.8 Ga All smaller than continents today Ur smaller than modern Australia Vaalbara ~3.3 Ga (theorized)

Ur ~3.0 Ga

Evolution of Ur ~3 Ga (“Giga” or billion years), Ur formed as a rare continent on Earth ~1 Ga, Ur was part of the supercontinent Rodinia ~300 Ma (million years), Ur was part of the supercontinent Pangea ~208 Ma, Ur was torn into parts of Laurasia and Gondwana ~ 65 Ma, the African part of Ur was torn apart as part of India Currently, pieces of Ur are in Australia, India, Africa and Madagascar

Arctica ~ 2.5 Ga Nuvvuagittuq gneiss 4.28 Ga Acasta gneiss 4.04 Ga

Evolution of Arctica ~2.5 Ga Arctica formed from Siberian & Canadian shields ~1 Ga Arctica became part of supercontinent Rhodinia ~750 Ma Arctica tore off Rhodinia becoming part of ProtoLaurasia ~320 Ma Arctica combined with several smaller land masses Ultimately forming part of Pangea ~208 Ma Arctica was torn apart as Pangea broke up Currently, pieces of Arctica are in Canada and Siberia

Atlantica ~2.0 Ga

Evolution of Atlantica ~2 Ga, formed from rocks now in South America and Africa ~1.8 Ga become part of supercontinent Columbia ~1.1 Ga Atlantica became part of Rodinia ~500 Ma Atlantica is part of Gondwana, then part of Pangaea ~208 Ma, Pangaea torn apart, splitting Atlantica Currently, remains of Atlantica are in Africa and South America

Nena ~1.8 Ga Arctica

Evolution of Nena ~1.8 Ga, formed from Arctica, Baltica and Antarctica becomes part of supercontinent Columbia ~1.5 Ga, survives breakup of Columbia intact ~1.1 Ga becomes part of Rodinia ~750 Ma, survives breakup of Rodina mostly intact ~600 Ma, becomes part of Pannotia ~540 Ma, Pannotia rifted, Nena torn apart Currently, the remains of Nena are in Canada, northern Europe, Siberia and Antarctica

Ancient supercontinents – one large landmass Columbia -- formed ~1800, rifted ~ 1500 Ma Rodinia -- formed ~ 1100, rifted ~ 700 Ma Pangaea Gondwana ~500 Ma joined Laurasia ~ 250 Ma rifted ~ 160 Ma Suggests a cycle of ~750 Ma ~500 Ma assembly ~250 Ma dispersal Supercontinent cycle  quasi-periodic aggregation and dispersal of crust  continents are constantly reconfigured as long as plate tectonics works Kenorland -- formed ~2700, rifted ~ Ma

Columbia: 1800 – 1500 Ma Ur Nena/Arctica Atlantica

Rodinia: 1100 – 700 Ma

Rodinia rifted into pieces that formed: 1. Proto-laurasia Congo Proto-gondwana

Congo, Proto-laurasia, -gondwana formed: Pannotia – short lived, ≈ 60 Ma

Pangaea: Ma 260 m.y. Gondwana Laurasia

Today..... But what about tomorrow?

Pangaea Ultima Amasia

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