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Is carbon dating appropriate for measuring the age
How do scientists know the bones are really 68 million years old?
Today's knowledge of fossil ages comes primarily from radiometric dating, also known as radioactive dating.
It can be used on objects as old as about 62,000 years. Atoms of the same element that have different numbers of neutrons are called isotopes. Most carbon on Earth exists as the very stable isotope carbon-12, with a very small amount as carbon-13.
When paleontologist Mary Schweitzer found soft tissue in a Tyrannosaurus rex fossil, her discovery raised an obvious question -- how the tissue could have survived so long?
The bone was 68 million years old, and conventional wisdom about fossilization is that all soft tissue, from blood to brains, decomposes.
To read the time on this radioactive clock, scientists use a device called a mass spectrometer to measure the number of parent and daughter atoms.
The ratio of parents to daughters can tell the researcher how old the specimen is.
As we mentioned above, the carbon-14 to carbon-12 ratio in the atmosphere remains nearly constant.
It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes and human activities.The result is like a radioactive clock that ticks away as unstable isotopes decay into stable ones.You can't predict when a specific unstable atom, or parent, will decay into a stable atom, or daughter.But you can predict how long it will take a large group of atoms to decay.The element's half-life is the amount of time it takes for half the parent atoms in a sample to become daughters.This plot shows the level of carbon-14 in the atmosphere as measured in New Zealand (red) and Austria (green), representing the Southern and Northern Hemispheres, respectively.Aboveground nuclear testing almost doubled the amount of carbon-14 in the atmosphere. The black arrow shows when the Partial Test Ban Treaty was enacted that banned aboveground nuclear tests. A special kind of radiocarbon dating: Bomb radiocarbon dating.Radiometric dating relies on the properties of isotopes.These are chemical elements, like carbon or uranium, that are identical except for one key feature -- the number of neutrons in their nucleus.Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.They have the same ratio of carbon-14 to carbon-12 as the atmosphere, and this same ratio is then carried up the food chain all the way to apex predators, like sharks.