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Unformatted text preview: Course Summary 1994 M6.7 Northridge earthquake, California Another building destroyed by the 1994 Northridge earthquake Devastation from 1995 M7.2 Kobe earthquake, Japan Whole neighborhoods were destroyed in the 1999 M7.4 Izmit earthquake in Turkey. More than 17,000 people were killed in this earthquake. Earthquakes can trigger tsunamis. This destruction was caused by the tsunami triggered by the 1964 M9.2 Alaskan earthquake. Many low-lying towns were destroyed by the tsunami triggered by the 1998 M7 Papua New Guinea earthquake Geologic Time Geologists use cross-cutting relationships to determine relative age of events. So, in this picture, (1) layers A-J were emplaced (A being the oldest, J the youngest), then (2) the pluton and dike intruded into these layers, and finally (3) the fault formed, creating an offset in the layers and the dike. Geological Time Scale Originally, a relative time scale (only knew if a rock was older or younger than some other rock - didn't know actual ages in years) Based on fossil record. Back in the Precambrian, there were essentially no fossils, so not a lot of detail to the geological time scale before the Cambrian. Relative age dating using fossils Fossils can be used to correlate rocks from place to place Absolute Time Get absolute dates from radiometric dating. Radiometric dating is based on the process of radioactive decay. Radioactive decay occurs when a neutron decays into a proton and an electron. The rate at which this decay occurs is measure in half-lives... Which parent-daughter pair is used for dating the rock depends on its minerals, age. Can now add dates to the Geologic Time scale. The oldest date on this time scale is 2.5 billion years. But how old is the earth? About 4.6 billion years old Oldest continental rocks: 4 billion years old Oldest oceanic rocks: a mere 200 million years old We know the age of the earth from radiometric dating of stoney meteorites (see below). These meteorites have never been heated above 100 degrees, so have never been part of a planet (other types of meteorites are bits of Mars, for instance). Evolution of the Solar System Evolution of the Solar System Evolution of the Solar System Evolution of the Solar System Evolution of the Solar System Our Solar System The whole solar system is about 4.6 billion years old. In the first step of the formation of our solar system, a gaseous cloud begins to collapse due to gravity. In the second step, a star forms and burns off its gases, and lastly the planets form. How do we know this? We can see it happening in other parts of the universe. Below are two pictures of nebula in the star formation stage taken by the Chandra X-Ray observatory satellite. We can also see stars die...this picture (also from Chandra) shows the remnants of a supernova explosion at the end of a star's life. We can observe the speed and direction at which galaxies are moving away from (and they're pretty much all moving away since the universe is expanding). We can then figure out that in the very distant past, all the galaxies were at the same place at the same time - The Big Bang, the birth of the universe, ~15 billion years ago. How do we know how fast galaxies are moving away from us? We can measure galactic velocities by measuring the redshift of their light, which is how much the light has shifted towards the red end of the light spectrum (similar to the Doppler shift that affects sound waves emanating from a moving source). Another way we can learn about the Big Bang and the birth of the universe: by measuring the Cosmic Microwave Background. The first observation of the cosmic microwave background was accidental... ...
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This note was uploaded on 09/05/2009 for the course GEOL 240Lxg taught by Professor 12:30-01:50pm during the Fall '07 term at USC.
- Fall '07