14_Historical Geology

14_Historical Geology - Lecture 14 Historical Geology Deals...

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Lecture 14 Historical Geology Deals with the origin of the Earth and its development through time. Strives to establish an orderly chronological arrangement of the physical and biological changes and events that have occurred in the geologic past. Geologic Time Previous estimates of the age of the Earth: Cooling through conduction and radiation (Lord Kelvin, 1897): ~24 – 40 m.y. Rate of delivery of salt to the oceans (John Joly, 1899-1901): ~90 – 100 m.y. Thickness of total sedimentary record divided by average sedimentation rates (1910): ~1.6 b.y. Oldest rocks on Earth found so far: 1. Acasta Gneisses in northwestern Canada near Great Slave Lake (4.03 Ga) 2. Isua Supracrustal rocks in West Greenland (3.7 to 3.8 Ga) 3. rocks found in the Minnesota River Valley and northern Michigan (3.5-3.7 billion years), in Swaziland (3.4-3.5 billion years), and in Western Australia (3.4-3.6 billion years) Oldest materials to be found on Earth: Zircon grains found in sedimentary rocks in west- central Australia = 4.4 b.y. 70 well-dated meteorites using different dating methods (e.g. Rb-Sr, Sm-Nd, Ar-Ar) = 4.4-4.6 b.y. Iron meteorite (Canyon Diablo meteorite) = 4.54 b.y. 1. Most accepted age for the Earth and the rest of the solar system: ~4.55 b.y. old (+ ~1%) 2. “Best” age of the Universe: 14 – 17 b.y. Relative Dating
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14_Historical Geology - Lecture 14 Historical Geology Deals...

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