Transcript Changing Earth

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
• 200 - 250 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
Permian – time of great
terrestrial and marine
connectivity but were
barriers – Central
Pangaean Mtn. range;
Pangaean Desert
W. Asia and Europe collide – Ural Mtn.; other continents
join to form Pangaea; East Asia isolated, Tethys Sea; One
great ocean – Pathalassa
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