01 JAN 2012 by ideonexus

 How Radiometric Dating Works

Briefly, a radioactive isotope is a kind of atom which decays into a different kind of atom: for example. one called uranium-238 turns into one called lead-206. Because we know how long this takes to happen, we can think of the isotope as a radioactive clock. Radioactive clocks are rather like the water clocks and candle clocks that people used in the days before pendulum clocks were invented. A tank of water with a hole in the bottom will drain at a measurable rate. If the tank was filled at...
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A great summary of how we date fossils using Uranium and Carbon atoms and their decay rates.

01 JAN 2010 by ideonexus

 The Perpetual Rain of Sediments to the Ocean Floor

For the sediments are the materials of the most stupendous 'snowfall' the earth has ever seen. It began when the first rains fell on the barren rocks and set in motion the forces of erosion. It was accelerated when living creatures developed in the suface waters and the discarded little shells of lime or silica that had encased them in life began to drift downward to the bottom. Silently, endlessly, with the deliberation of earth processes that can afford to be slow because they have so much ...
Folksonomies: nature
Folksonomies: nature
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Dust from deserts, minerals from rivers, and shells from lifeforms in the ocean are constantly raining down onto the ocean floor.