Historical Geology - Lunar and Planetary Institute

Historical Geology - Lunar and Planetary Institute

Plate Tectonics A Brief History of a Unifying Theory Plate Tectonics as the Unifying Concept of Earth Science

Accumulation of Observations Evidence Patterns of continents Paleontology Geology Patterns of sea floor ages Patterns of seafloor depth Patterns of seafloor

sediments Patterns of magnetism Patterns of volcanoes Patterns of earthquakes Earths Great Puzzle Pieces

1620 Sir Francis Bacon observed similarities of coasts of Africa and South America no mere accidental occurrence. A few years later it was suggested that they were once one, but had been separated by the Flood.

1782 Benjamin Franklin, based on observed oyster shells on mountain tops The crust of the Earth must be a shell floating on a fluid interior.... Thus the surface of the globe would be capable of being broken and

distorted by the violent movements of the fluids on which it rested. 1799 Alexander Von Humbolt, German explorer and naturalist, observed the similarities in the

geology and features of the west coast of Africa and east coast of South America (separated by a valley filled by the flood) http://pubs.usgs.gov/gip/dynamic/historical.html 1858 - Geographer Antonio Snider-Pellegrini

made these two maps showing his version of how the American and African continents may once have fit together, then later separated A Man and His Model Current: Contracting Earth 1912: Continental Drift Observations

Fit of Continents Geology Paleontology Climate belts Pangaea (all lands) 300 to 200 Ma Breakup 180 Ma

Alfred Wegener Rigid bodies moving through Scientific Community says: Scientific Community says:

No Mechanism to Make Continental Drift Happen Mechanism for Plate Movement! Arthur Holmes (Late 1920s) Interior of Earth has sluggish convection (transport of heat from core); hot stuff rises, cool stuff sinks

New ocean crust injected into ocean floor (where?) Maurice Ewing Mapping the seafloor 19471959 Lockney Texas Rice University Trained UTMB - Division of Earth

and Planetary Sciences of the Marine Biomedical Institute Maurice Ewing Mapping the seafloor 1947-1959 Surprises:

Thin sediment Basalt crust glasses Age less than 150 Ma (hadnt identified a pattern yet) Ridges later shown to circle globe Valley within ridge (Tharp) Earthquakes along ridges

High heat flow (Bullard) Harry Hess and Seafloor Spreading 1962 startling new theory History of the Oceans New ocean crust at midocean ridges Ocean crust dragged down at trenches; mountains

form here Continental crust too light; remains at surface Earthquakes occur where crust descends It explains everything. Rocks and Magnetism - Tools

When magma cools, takes on signature of Earths prevailing magnetic field Three magnetic measurements can be taken from rocks Inclination - ~ latitude ~distance to the pole Declination - ~ direction to the

pole Positive (normal) or negative (reversed) - depending on what Earths field is doing Add age = powerful tool You are Here!

Magnetic Reversals Earths present magnetic field is called normal magnetic north near the north geographic pole magnetic south near the south geographic pole At various times in the past, Earths magnetic field has completely reversed magnetic south near the north geographic pole

magnetic north near the south geographic pole 171 times in last 76 million years take 5,000 to 10,000 per reversal; last 10s of thousands to millions of years review your storage media Vine and Matthews The Final Push

Symmetric patterns of magnetism on either side of mid-ocean ridge Magnetic Stripes on Seafloor Seafloor as a magnetic tape recorder Oceanic Crust Is Young

Age of Continents Original copyrighted image removed; ;there is an image available at http://www.lithosphere.info/TC1-2006/TC1_Fig2-ages- 062006.jpg

that may be copyrighted. Tuzo Wilson A Final Blow Transform faults: opposite sense of movement than expected. Proven correct (Sykes) Sealed theory of sea-floor spreading and plate tectonics

for most scientists Theory of Plate Tectonics The upper mechanical layer of Earth (lithosphere) is divided into rigid plates that move away from, toward, and along each other Most deformation of Earths crust occurs at plate boundaries How can you calculate the

rate of plate movement? Pick an object and watch it Better on glaciers than on slow moving plates Use magnetic reversals long time periods Date rocks across a mid-ocean ridge really

really carefully tedious Hot Spots Stationary magma chambers under mobile plates Prominent Hot Spots

Plate Movement Rates using Hot Spots http://www.classzone.com/books/earth_science/terc /content/investigations/es0810/es0810page01.cfm? chapter_no=investigation Tectonics on Other Planets?

Do you recognize either of these locations? Mars Topography Mars Magnetic Field

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