Best method for dating fossils




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Potassium-argon dating , Argon-argon dating , Carbon or Radiocarbon , and Uranium series.


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All of these methods measure the amount of radioactive decay of chemical elements; the decay occurs in a consistent manner, like a clock, over long periods of time. Thermo-luminescence , Optically stimulated luminescence , and Electron spin resonance. All of these methods measure the amount of electrons that get absorbed and trapped inside a rock or tooth over time.

Since animal species change over time, the fauna can be arranged from younger to older. At some sites, animal fossils can be dated precisely by one of these other methods.

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Dating Fossils – How Are Fossils Dated?

Last year, the University of Colorado's Doug Bamforth analyzed a cache of plus tools that a Boulder, Colorado, man accidentally unearthed in his yard. Those tools showed protein residue from camels and horses, so Bamforth dated them to the Clovis people who lived around about 13, years ago.

Not all scientists accept the accuracy of these tests, but that's nothing new in archaeology. Medieval manuscripts have a lot more to say than simply the words on their pages; often they're written on parchment made from animal skins, and organic material keeps its secrets for a long time.

Why Dating Methods Can Date Nothing

Literary historian Timothy Stinson developed a way to extract the DNA from parchment itself, and if you can tell what animal a parchment was derived from, you might be able to tell more about what time and place the document originated. Moa, the giant flightless birds of New Zealand, may have been extinct for at least years, but their dung is surprisingly resilient.

On cave floors and buried in shelters, researchers found dung from the moa, with some of the samples being 15 cm nearly six inches in length. The contents of the droppings give more than a window into the giant bird's eating habits—they preserve a record of what the long-gone moa's ecosystem was like. The arid conditions of New Zealand caves provide the perfect place for poo preservation. Australia should, too, the researchers say, but the droppings of ancient marsupials just haven't turned up.

As professor Alan Cooper says, "A key question for us is 'where has all the Australian poo gone? If you think your metal detector has uncovered some treasures, try finding vintage plutonium in the backyard. Jon Schwantes of the Pacific Northwest National Laboratory was called in to analyze a sample of plutonium accidentally discovered in a safe during the cleanup of the Hanford nuclear site in Washington.

Relative Dating

One clue was the "signature" left by the reactor—every reactor's is different. The fingerprint of this discarded material led him to a reactor not in Hanford, but in Oak Ridge, TN. It also led him to the conclusion that it was created in , meaning it was created during the Manhattan Project, making it one of the world's oldest-known samples of enriched plutonium. A pile of skeletons probably wouldn't tell us much more than the obvious.

Dating | The Smithsonian Institution's Human Origins Program

But University of Leicester archaeologist Simon James sees evidence that, to him, dates the first known chemical warfare attack back to A. In that year, Persians attacked a Roman garrison at Dura-Europos in Syria; when they tried to mine under the walls, Romans tried to counter by mining under the Persian tunnels. Archaeologists found the pile of Roman bodies in one of the tunnels, but no cause of death. James thinks it was asphyxiation. In the tunnels, he says, there was bitumen and sulfur—materials that, when burned, give off toxic gas.

So, he says, the Persians probably used chemical warfare to do in their rivals. One classical way to date objects is to take note of what strata of rock they occupy—rocks come in layers, with the oldest at the bottom.

But those rocks also carry less obvious information—their magnetic signatures. The Earth's magnetic field varies all the time, by both strength and orientation.

DEPARTMENTS

At the time rocks form, however, their magnetic materials acquire the particular orientation of the planet's magnetism at the time, giving geologists a window into the Earth's magnetic past. You've probably heard about ice cores, but what are they exactly? Ice sheets are laid down in layers, and the layer corresponding to each year is a little different. The important thing for climate researchers is that the oxygen isotopes present in a layer can help show what the temperature was that year.


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  5. So by extracting a cylindrical core sample containing layers that go way back, they can build a model of the climate of the past. Finally, pollen is good for something besides making you sneeze. Deposits of pollen deep in the ground can reveal what the vegetation was like at that time, and ergo, what the area's climate might have been like.

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