Continental Drift Lyell proposed movement of continents to account for climate change evident in fossil record BUT did not change shape or position relative to each other

Continental Drift Tyler proposed crustal changes to account for mountains and island chains

Continental Drift Tyler proposed crustal changes to account for mountains and island chains

Continental Drift Wegener Observations Alignment of mountains and rock strata matched on opposite sides of Atlantic Glacial deposits displaced towards North Pole Coal belt of N. Amer. and Europe suggested tropics

Continental Drift Wegener’s conclusions Continental rock, sial (silicon and Al) lighter than ocean floor (basalt), continents float on fluid mantle Once a supercontinent, Pangaea, that broke into smaller plates Breakup began as rift valley and widened into ocean

Continental Drift Continental blocks (plates) retained their shape except where mountain building (can still join the plates now separated) Movement of plates different Radioactive heating from mantle causes plate movement

Late Supporting Evidence Computer mapping fit continental shelf of continents together Discovery of submarine volcanoes (guyouts) Ocean floor is basalt and younger than continental rock (max. 150 mya vs. > 1 billion for continental rock) Midoceanic ridge, continuous 65,000 km system on seafloor Magnetic anomalies from differential deposition of magnetized rock

Tracking Continental Movement – Remnant Magnetism

Major Tectonic Plates

Age of islands relative To distance from rift zone

Drift and Life 600 – 650 mya first multicellular life 475 – 525 mya Cambrian explosion 400 – 450 mya first life on land, including vertebrates and plants ~360 mya first reptiles mya first mammals and birds

Gondwanaland – 650 – 475 mya – oldest continuous land mass

N. Amer. and N. Europe (PA) begin drift north

NA, N. Europe & Siberia eventually collide to form Laurasia Gondwanaland drifts north

W. Asia and Europe collide – Ural Mtn.; other continents join to form Pangaea; East Asia isolated, Tethys Sea; One great ocean – Pathalassa Permian – time of great terrestrial and marine connectivity but were barriers – Central Pangaean Mtn. range; Pangaean Desert

Break up of Pangaea Formation of Pangaea brought together biota formerly isolated Diversification of Pangaea and Pathalassa probably resulted from breakup (180 mya) by creating isolation Breakup began when Turgai Sea expanded from Arctic to split Asia and Euramerica Separation N. America and Europe by shallow “Atlantic Sea”

Break up of Pangaea Tethys Seaway opened Gulf of Mexico formed with separation of N. and S. America

N. America and Europe reconnect (Beringea landbridge) NA epicontinental sea

M and I separate; I moves toward Asia (collide ~60 mya); AU separates from Antarctica severing link to S. Amer. Many small plate collisions (65 – 2 mya)

Great American Interchange – reconnected NA and NT ~4 mya (last connected ~160 mya)

Hotspots – fixed, weak points in crust

Epicontinental (Epeiric) Seas Changes in continent location and sea levels Formed barriers on terrestrial landscape Australia divided into three parts in Cretaceous (50 mya) North America – several epeiric seas – most recent ended ~65 mya Europe and Asia separated by Turgai Sea until ~30 mya

Paleoclimate Relative amount of land/ocean and distributions also influence solar radiation and temperature  climate, winds, and currents Example – warm circum-equitorial currents (Tethys Seaway) replaced by cold currents

Consequences of Plate Tectonics Profound effects on both terrestrial and aquatic biota Constant, albeit slow, change –Plates form, expand, merge, separate –Plates eliminated by subduction and consumed –Change shape These dynamics allowed flow but also isolation through barriers

Effect of lowering sea level on marine diversity (loss of seas

Seafloor spread and number of species

Boxes in this chapter rich with information. Among most useful are Tables 8.2 and 8.3