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(meteorobs) Re: Age Dating of Rocks:The Earth, and Solar System Compared

Here's the 2nd part of Frank's explanation on Age dating of Rocks.
George Zay

<< 
 	I would like to continue my disscusion now with a look at the 
 early Earth. I will focus on how ages help us correlate events on the 
 early Earth. 
 	The early Earth was a molten mass being constantly being 
 bombarded by meteorites. The radioactive components of these meteorites 
 contributed to the heating of the Earth, and so it took longer to cool. 
 When the Earth finaly started to cool, all the radioactive components of 
 meteorites had been used up(Half-life). 
 	What was the radioactive component that heated the Earth? 
 Aluminum 26. If you read about the Allende meteorite you will come across 
 the term Ca/Al inclusion(calcium/ aluminum inclusion). These inclusions 
 provide direct evidence that an unstable element decayed at a fast rate, 
 thus providing fuel for the fire so to speak. 
 	Al 26 has a half life of 700,000 yrs, and so has been used up 
 since the formation of the Solar System. This is how we date those 
 inclusions, and give us an upper limit of the age of the Solar System of 
 5 billon yrs.
 	Now, Al 26 has to be incorporated into the Earth. As I said 
 earlier, meteorite impacts provide the best source. This combined with 
 the fact that the Earth also incoporated billions of Chondrules from the 
 early solar nebulae, provide enough unstable elements to heat the Earth 
 up. We still see the remenents of this episode everytime we watch a 
 volcanoe erupt. Those components still keep the Earth warm.
 	So what does this mean? It gives us a way to compare the age of 
 the Earth with the Solar System. We can compare the oldest rocks here on 
 the Earth, and the age of meteorites to see how long it took to develop 
 the Earth from a molten mass, to a planet with an outer crust. 
 	We use this time to develop working models of planetary 
 formation, and cooling. If a body the size of the Earth takes so long to 
 cool to a certain point, than we can calculate how long other bodies take 
 to cool. Cooling gives a view of the interiors of planets, and how long 
 they took to form, and what are they composed of. 
 	So, as you can see, age dating on Earth gives a little more than 
 just a time of formation. It also give how, and why. These are 
 fundemental answers to questions that needed answers. The question now 
 is: Where does this take Planet Earth?
 
 
 Frank Stroik
 
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