Age of the Earth

Subdivisions of geologic time –Eon, Era, Period, Epoch –Eons Precambrian: 4.5 b.y. to ~0.5 b.y. Phanerozoic: ~0.5 b.y. to today Geologic time scale

Subdivisions of geologic time –Eon, Era, Period, Epoch –Eras Paleozoic: ~560 m.y. to ~250 m.y. Mesozoic: ~250 m.y. to ~65 m.y. Cenozoic: ~65 m.y. to today Geologic time scale

Image source:

Plate Tectonics- Overview Plate Tectonics–General Principles Plate Movements–Accumulating Evidence Types of Plate Boundaries How Far, How Fast, How Long, How Come? Plate Tectonics and the Rock Cycle

Plate Tectonics–General Principles Stress and Strain in Geologic Materials Lithosphere and Asthenosphere Locating Plate Boundaries

Tectonics Stress- application of a force –Compressive (pushing together) –Tensile (pulling apart) Strain- deformation response of the force –Elastic deformation: ‘rubber band’ –Plastic deformation: permanent strain –Rupture: the breaking point

Folding Rock Source: Photograph courtesy of M.R. Mudge; courtesy USGS Photo Library, Denver, CO.

Folding and Faulting, Cook Inlet, Alaska Source: Photograph by N.J. Silberling, USGS Photo Library, Denver, CO.

Rock Failure Under Stress Source: Photograph courtesy of W.B. Hamilton; courtesy USGS Photo Library, Denver, CO.

Effect of tectonics on rocks Depends of physical conditions –Temperature & pressure –composition, time, fluids

Lithosphere- Asthenosphere

Lithosphere-Asthenosphere Lithosphere (lithos = rock) –Brittle, elastic outer layer –~50 km under oceans, ~100 km under continents Asthenosphere (asthenes= without strength) –Plastic domain –~300 km in mantle –Discovered by seismic wave studies

Plate boundaries Deformation, earthquakes, and volcanoes are not evenly distributed around the Earth Mostly concentrated in linear belts, chains Can use distribution to ‘map out’ plates ~8 major plates, several smaller ones

World Locations of Volcanoes and Earthquakes Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey.

Plate Movements–Accumulating Evidence The Topography of the Sea Floor Magnetism in Rocks–General Paleomagnetism and Seafloor Spreading Age of the Ocean Floor Polar-Wander Curves Other Evidence

Shaded Relief Map of the World Source: Photo courtesy of NOAA National Geophysical Data Center.

Shaded Relief Map of the World Source: Photo courtesy of NOAA National Geophysical Data Center.

The Earth is a large bar magnet… And sometime it flips…!

(1) Minerals oriented randomly in a melt (2) Minerals aligned in the magnetic field Minerals: the ‘Curie Temperature’

First magnetic survey of the oceans

Age Distribution of the Sea Floor Source: Marine Geology and Geophysics Division of the NOAA National Geophysical Data Center.

World Locations of Volcanoes and Earthquakes Source: Map plotted by the Environmental Data and Information Service of NOAA; earthquakes from U.S. Coast and Geodetic Survey.

World Lithospheric Plates Source: After W. Hamilton, U.S. Geological Survey.

Source: Polar Wander

Plate Movements — Today Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75: , 1970, copyright by the American Geophysical Union.

Plate Movements — 100 Million Years Ago Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75: , 1970, copyright by the American Geophysical Union.

Plate Movements— 200 Million Years Ago Source: After R.S. Dietz and J.C. Holden, “Reconstruction of Pangaea,” Journal of Geophysical Research, 75: , 1970, copyright by the American Geophysical Union.

Glacial Deposits Across Southern Continents Source: After Arthur Holmes, Principles of Physical Geology, 2d ed., Ronald Press, New York, NY, 1965.

Types of Plate Boundaries Divergent Plate Boundaries –Rifts, Mid ocean ridges, lots of volcanism Transform Boundaries –Sliding plates, lots of earthquakes Convergent Plate Boundaries –Subduction zones, mountain belts

Divergent plate boundary: East African Rift

Satellite Image of Lake Tanganyika, Africa Source: © NASA

Transform plate boundary: San Andreas strike-slip fault

Convergent plate boundary: Subduction Zone in Alaska Source: Image courtesy of NOAA National Geophysical Data Center.

Convergent plate boundary: Where are we?

Current Motions of Major Plates: Satellite laser data Source: Data from NASA.