G1-Lecture03-Engineering-Geology

G1-Lecture03-Engineering-Geology - CEGCEG-4011 Geotechnical...

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CEG CEG-4011 Geotechnical Engineering I 4011 Geotechnical Engineering I Lecture #03 A brief overview of Engineering Geology L. Prieto-Portar, 2009
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This radio map of the young star HLTau (center), is surrounded by a disk of gas and dust outlined within the white ellipse. The hot gases from the star are flowing in the direction of the white arrows. A proto-planet “b” lies at a distance to HL Tau about twice that as Neptune does from our sun. HL Tau is about 520 light-years from Earth, and is only 10 5 years old (Science News, 5 April 2008).
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Our planet is about 5,000 million years old, formed from gaseous origins that slowly cooled to the partly solid Earth of today. About 4,000 million years ago a space object about the size of Mars impacted the young Earth, and tore out a terrestrial chunk of mantle into an Earth orbit to become our Moon. The Moon’s low density is similar to our mantle. The Moon has been confirmed to be similar geologically to the Earth. Only 65 million years ago, a smaller meteor, 16 km in diameter, struck our Earth again. The ensuing clouds of dust killed most of the vegetation, and lead to the extinction of dinosaurs. The evidence of this disaster is a thin layer of space-borne Iridium between the Cretaceous and the Paleogene Periods. About 4,600 million years ago, a solid crust formed with temperatures in excess of 100ºC. There was no rain, but the Earth was shrouded in heavy clouds which was our proto-atmosphere. Cooling below 100ºC brought rain and initiated weathering. But this occurred only 250 million years ago! There was little oxygen, since today’s atmosphere is largely a product of photosynthesis. These early soils are called proto-soils. Some are still visible in Africa and northern Europe as granites, 3,500 million years old.
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A rendered view of a meteorite hurling towards the Earth.
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Artist’s representation of the impact of an asteroid upon Earth.
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The crust has a thickness of about 10 to 40 km. It is mostly made up of light silicates with an average ° = 3 g/cm 3 . The upper and lower mantle is about 3,000 km thick, and is made up of metallic silicates and sulfides with ° = 3.5 to 6 g/cm 3 . The liquid core is about 2,100 km thick, and is made up primarily of liquid Fe and Ni, with a ° = 10 Dimensions (in kilometers) of the three main components of the planet Earth. g/cm 3 . Finally, the solid inner core has a diameter of 1,300 km and a ° = 13 g/cm 3 . Richard Oldham of Great Britain was the first physicist to study seis- mology. A few years later, the Cro- atian physicist Andrija Mohorovicic use it to map the boundary between the mantle and the crust (now known as the “Moho” discontinuity.
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Sun’s core as a comparison to the Earth’s.
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If it were possible to break down all the matter found on the Earth, its constituent elements would be distributed as shown to the left.
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