Posted on 06/05/2008 5:52:39 AM PDT by Homer_J_Simpson
With the aid of lead, Harvard physicists hope to trace the earth’s history back further than ever before into the ages following this planet’s birth from the sun.
For a timepiece scientists have used uranium-lead, a “dead” end-product of uranium’s disintegration. Because they know how long it takes uranium to “die,” they can tell how old a deposit is from the proportion of live uranium and inactive uranium-lead found side by side. Mineral deposits have thus been dated back nearly 2,000,000,000 years. Many geologists estimate that the earth may be much older than this – perhaps 3,000,000,000 years old.
The new Harvard finding concerns ordinary or common lead, which may be called the “older brother” of uranium-lead. Ordinary lead is as old as earth itself. It was included in the molten mass of the earth before it cooled down. The different kinds of lead are indistinguishable chemically, but the physicist detects them by their slightly different weights. Such elements are called “isotopes.”
Ordinary lead has four isotopes, weighing 204, 206, 207 and 208 atomic units. It was found at Harvard that the relative abundances of these isotopes may vary as much as 15 per cent. Before that scientists had always believed that isotopes of ordinary lead had a certain, fixed ratio.
The discovery was made by Dr. Alfred O. Nier, National Research Fellow in the Harvard Physics Laboratories, with the most delicate atom “sifter” known to science, a mass spectrometer. Dr. Nier’s instrument is of a new type. It is so sensitive that it can quickly determine the exact amount of lead isotope 204 in a specimen. When this is known the amount of ordinary lead mixed in a radioactive deposit can be calculated.
The peculiarity of isotope distribution in ordinary lead was not previously discovered because the variations in abundance of the four isotopes are such that their weighted average, or the atomic weight of lead, was always found to be precisely 207.21 atomic units. Hence it was never thought that the ratio of the isotopes might vary.
Ordinary lead’s isotope distribution dates back millions of years. It was probably caused by the early “contamination” by the lead formed from the radioactive elements uranium and thorium, Dr. Nier believes. This theory has yet to be thoroughly investigated.
Dr. Nier found that the oldest deposits of ordinary lead tend to have more of the isotope 204 in proportion to the isotopes 206, 207 and 208 than the younger deposits. Ordinary lead, which has the isotopes 204, 206, 207 and 208, is the only lead to have the isotope 204; uranium-lead comes in two isotopes, 206 and 207, and thorium ends up in lead which weights 208 units.
By tracing back this ancient peculiarity, scientists may find that the ordinary lead atom carries within it at least a partial record of physical and chemical developments when the earth was young. For one thing, a continuation of this study promises to reveal important clues as to the mechanism of the formation of lead ores.
Dr. Nier has also derived an entirely new method of determining the age of uranium-lead by a comparison of the ratio of uranium-lead isotopes 206 and 207, eliminating altogether the necessity for determining the amount of uranium still alive in a deposit. This provides a means of making a second, independent measure of the age of a deposit and thus checking the age as determined by the lead-uranium ratio.
NO! Just a few more and I will give it a rest for a few days. This one is highly scientifical.
“Clue to Earth’s Beginning”
Genesis 1:1 “In the beginning, God created the and the earth.”
Cool.
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These Blasts from the Past that have been going on for a while are kinda cool, here's one germane to GGG. |
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