EPS 102 Lecture 7 - EPS 102 Lecture 7 Tuesday February...

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EPS 102 Lecture 7 Tuesday February 10 th , 2009 Meteorites: tell you something about where we all come from and what we are all made of. Meteorites are imaged coming into the atmosphere and sometimes found. Cameras and telescopes scan the sky that look for objects in the sky. In the late 1700s enough meteorites had been collected and backed by credible stories so the science was then established. Meteorite: the rock fragments; materials that fall out of the sky and come to earth. Meteoroid: the smaller version of meteorites. We see these more often because there are more of them. Meteor: track of light, or a shooting star. The piece of dust that made that track of light doesn’t make it all the way to the surface. Meteor flashes, or showers, are when the Earth passes through the debris or the tail left over from a comet. Meteor showers are flashes that might be a few per minute. We have evidence of meteorites that have fallen in the past due to craters. In the US, there is one a mile across which is only a few million years old. This is not a volcanic type crater. Crater means hole in the ground. We will refer to impact craters, and they aren’t volcanic because there is no volcanic material, and because there are minerals in this rock that form at very high pressures= 50,000 atm. You can transform quartz into a high pressure form, and the speed of the impact could be inferred. There are a few craters around the world, around 100. Some of them are quite eroded, and some are home to a lake. A lot of debris comes down on Earth all the time. Small fluffy grains that come into the atmosphere. You can collect this material while it’s in the atmosphere and measure how many particles you get. Fewer grains come into the atmosphere if they are large. But tons of material comes into the atmosphere on a yearly basis. Small craters are made on Earth on the yearly basis, and a lot of impacts happen in the ocean. Then you can get km sized craters on thousand year time scales. Mass extincting major impacts happen on many tens of millions of years to hundreds of millions of years. Atmospheric explosions also occur. An explosion happened in Siberia that flattened a forest as big as the D.C. metro area. These kinds of major events probably happen on a century time scale. World population is so much now that it is likely we will see an event. There are two classes of meteorites: rocky and metal meteorites. Rock meteorites are called stone meteorites and metal meteorites are called iron meteorites. Rock ones are made of a minerals inside the earth like olivine, pyroxene as well as materials on the earth. There are chondrites, and achondrites. Of the falls (meteorites that are observed to have fell), only 6-7% are the iron meteorites. 90-95% are stony meteorites like the ordinary chondrites, achondrites, and carbonaceous chondrites. If you come across a stony meteorite, it’s hard to tell that it is a meteorite because it looks like a normal rock. A stony meteorite is hard to notice when you stumble upon it. In contrast, an iron
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This note was uploaded on 02/04/2010 for the course EPS 102 taught by Professor Staff during the Spring '08 term at University of California, Berkeley.

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EPS 102 Lecture 7 - EPS 102 Lecture 7 Tuesday February...

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