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Isotopic dating is based on

These basalts yield ages of up to 1 million years based on the amounts of potassium and argon isotopes in the rocks.But when we date the rocks using the rubidium and strontium isotopes, we get an age of 1.143 billion years.Yet lava flows that have occurred in the present have been tested soon after they erupted, and they invariably contained much more argon-40 than expected.1 For example, when a sample of the lava in the Mt. Helens crater (that had been observed to form and cool in 1986) ( age yield incorrect old potassium-argon ages due to the extra argon-40 that they inherited from the erupting volcanoes, then ancient lava flows of unknown ages could likewise have inherited extra argon-40 and yield excessively old ages.There are similar problems with the other radioactive “clocks.” For example, consider the dating of Grand Canyon’s basalts (rocks formed by lava cooling at the earth’s surface).No geologist was present when the rocks were formed to see their contents, and no geologist was present to measure how fast the radioactive “clock” has been running through the millions of years that supposedly passed after the rock was formed.No geologists were present when most rocks formed, so they cannot test whether the original rocks already contained daughter isotopes alongside their parent radioisotopes.

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New evidence, however, has recently been discovered that can only be explained by the radioactive decay rates not having been constant in the past.9 For example, the radioactive decay of uranium in tiny crystals in a New Mexico granite ( yields a uranium-lead “age” of 1.5 billion years.Because of such contamination, the less than 50-year-old lava flows at Mt.Ngauruhoe, New Zealand (), yield a rubidium-strontium “age” of 133 million years, a samarium-neodymium “age” of 197 million years, and a uranium-lead “age” of 3.908 billion years!Part 2 explains how scientists run into problems when they make assumptions about what happened .An hourglass is a helpful analogy to explain how geologists calculate the ages of rocks.Based on these observations and the known rate of radioactive decay, they estimate the time it has taken for the daughter isotope to accumulate in the rock.However, unlike the hourglass whose accuracy can be tested by turning it upside down and comparing it to trustworthy clocks, the reliability of the radioactive “clock” is subject to three unprovable assumptions.We find places on the North Rim where volcanoes erupted after the Canyon was formed, sending lavas cascading over the walls and down into the Canyon.Obviously, these eruptions took place very recently, after the Canyon’s layers were deposited ().When we look at sand in an hourglass, we can estimate how much time has passed based on the amount of sand that has fallen to the bottom.Radioactive rocks offer a similar “clock.” Radioactive atoms, such as uranium (the parent isotopes), decay into stable atoms, such as lead (the daughter isotopes), at a measurable rate.

989 comments

  1. RADIOMETRIC TIME SCALE. clock used for dating purposes is based on the radioactive decay of. a mass spectrometer to determine its carbon isotopic.

  2. Radiometric dating or radioactive dating is a. correlation between different isotopic dating methods may be. Dating methods based on extinct radionuclides can.

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