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. Only hard parts, like bones and teeth, can become fossils. But for some people, the discovery raised a different question. How do scientists know the bones are really 68 million years old?
Accurate dating of samples requires that the parent radioactive isotope has a long enough half-life such that it will still be quantifiable today.
So, what are our options? Since there is insufficient uranium present in dinosaur bones to date directly, scientists go for igneous rock rock formed from magma - usually in the form of a mineral called zircon ZrSiO 4.
Only hard parts, like bones and teeth, can become fossils. But for some people, the discovery raised a different question. 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. Radiometric dating relies on the properties of Author: Tracy V. Wilson. The preferred method of dating dinosaur fossils is with the radiometric dating method. And the result of this accepted method dates dinosaur fossils to around 68 million years old. However: Consider the C decay rate.
Zircon is ideal because:. Once the absolute age of a piece of zircon has been determined, it is matched to the sedimentary layers that it was found in. Dinosaur bones that are found in the same layer can then be dated based on this with a certain degree of accuracy.
Rock face showing the layers that have slowly been deposited over many years. In terms of charge, they are identical, meaning that they have the same chemical properties.
However, mass spectrometry MS can be employed to exploit their differences in mass. There exist many different variations of mass spectrometry, but they work by a similar principle.
Carbon-14 dating decontaminated dinosaur bones
The sample is first vaporized turned into gas and ionized turned into positively charged ionsthen accelerated along the length of a tube. Mass analyzers placed at the end of the tube are able to detect these, hopefully with enough sensitivity to tell the isotopes apart.
May 6, May 10, May 24, Usually, atoms have an equal number of protons and neutrons. If there are too many or too few neutrons, the atom is unstable, and it sheds particles until its nucleus reaches a stable state.
Think of the nucleus as a pyramid of building blocks. Eventually, some of the blocks can fall away, leaving a smaller, more stable structure. The result is like a radioactive clock that ticks away as unstable isotopes decay into stable ones.
But you can predict how long it will take a large group of atoms to decay. The more parent isotopes there are - and the fewer daughter isotopes - the younger the sample.
The half-life of the isotope being measured determines how useful it is at dating very old samples. The short half-life is only part of the problem when dating dinosaur bones - researchers also have to find enough of the parent and daughter atoms to measure.
Read on to see what it takes to date a fossil and what volcanic ash has to do with it. The most widely known form of radiometric dating is carbon dating.
This is what archaeologists use to determine the age of human-made artifacts. The half-life of carbon is only 5, years, so carbon dating is only effective on samples that are less than 50, years old. Dinosaur bones, on the other hand, are millions of years old - some fossils are billions of years old.
Radiometric dating. Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. Radioactive elements decay The universe is full of naturally occurring radioactive elements. Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into. Radiometric Dating. Radiometric dating involves exploiting the radioactive decay of unstable atoms naturally present in the structure of bones and rocks. These unstable atoms (radioactive isotopes) have a known 'half-life', which is the amount of time it takes for half of the isotopes in a given sample to undergo decay. Third, many dating methods that don't involve radioisotopes-such as helium diffusion, erosion, magnetic field decay, and original tissue fossils-conflict with radioisotope ages by showing much younger apparent ages. These observations give us confidence that radiometric dating is .
To determine the ages of these specimens, scientists need an isotope with a very long half-life. The extreme temperatures of the magma would just destroy the bones.
Carbon, Radiometric Dating and Index Fossils Carbon dating is used to determine the age of biological artifacts up to 50, years old. This technique is widely used on recent artifacts, but educators and students alike should note that this technique will not work on older fossils (like those of the dinosaurs alleged to be millions of years old). Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it. Relative Dating The majority of the time fossils are dated using relative dating techniques. Using relative dating the fossil is compared to something. The most widely known form of radiometric dating is carbon dating. This is what archaeologists use to determine the age of human-made artifacts. But carbon dating won't work on dinosaur bones. The half-life of carbon is only 5, years, so carbon dating is only effective on samples that are less than 50, years old.