Age of Earth estimates through time
Linnaeus
Wallace
Modern radioactive dating
Half life
Oldest fossil
Photoautotrophic prokaryote from Australia/South Africa (~3.5 bill yrs BP)
Alfred Wegener (1880-1930)
• Proposed the theory of continental drift in early 1900’s
• Who’s original idea?
• Antonio Snider-Pelligrini (1858)
• Mechanism not explained
Matching sequence of rock strata on different continents
Precambrian shields Flood Basalts
Stratigraphic evidence
Paleomagnetic evidence
• Orientation of the magnetized crystals at the time of mineral formation
• Earth reverses its magnetic north at variable intervals
Paleomagnetic evidence
• Seafloor record of remnant magnetism (magnetic stripes)
• Every 104 – 106 years
Black - regular,
White – reversed
Computer models – 1965
Marine geology after WWII
• Oceanic floor samples
• Echo soundings
• Oceanic ridges
• Abysall plain
• Denser than continental
• < 150 my old
Continental Drift – continents were once united and have since become independent structures that have been displaced all over the globe
Plate Tectonics – study of the origin, movement and destruction of plates and how these events have been involved in the evolution of Earth’s crust
Plate tectonics
Crust Continental (felsic)
Oceanic (mafic)
Mantle
Lower lithosphere
Asthenosphere
Outer Core
Inner Core
Plate tectonics
19 major tectonic plates
Plate Boundaries
Divergent boundaries
Convergent boundaries
Transform boundaries
Tectonic history of the continents
Reconstruction of tectonic history
• Paleomagnetic declinations
• Symmetrical magnetic stripes
• Topographic and bathymetric maps
• Lithologic indicators of climate
Tectonic history of the continents
Break up of Pangaea (initiated 180 mya)
• Laurasia rifting
• Landbridges broken
• Gondwanaland
began to separate
Tectonic history of the continents
Most of Gondwanaland separated (100 mya)
Landbridges btwn Europe and NA
Tectonic history of the continents • All continents separated (50 MYA)
• India about to collide with Eurasia (20 cm per year!)