The discovery of means for absolute dating in the early s was a huge advance. The methods are all based on radioactive decay:. The first radiometric dates, generated about , showed that the Earth was hundreds of millions, or billions, of years old. Since then, geologists have made many tens of thousands of radiometric age determinations, and they have refined the earlier estimates.
Age estimates can be cross-tested by using different isotope pairs. Results from different techniques, often measured in rival labs, continually confirm each other.
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Every few years, new geologic time scales are published, providing the latest dates for major time lines. Older dates may change by a few million years up and down, but younger dates are stable.
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For example, it has been known since the s that the famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65 million years old. Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. It is accurate to within a few thousand years. The fossil record is fundamental to an understanding of evolution. Fossils document the order of appearance of groups and they tell us about some of the amazing plants and animals that died out long ago.
Fossils can also show us how major crises, such as mass extinctions, happened, and how life recovered after them. If the fossils, or the dating of the fossils, could be shown to be inaccurate, all such information would have to be rejected as unsafe. Geologists and paleontologists are highly self-critical, and they have worried for decades about these issues. Repeated, and tough, regimes of testing have confirmed the broad accuracy of the fossils and their dating, so we can read the history of life from the rocks with confidence.
Educators have permission to reprint articles for classroom use; other users, please contact editor actionbioscience. Currently, he is studying certain basal dinosaurs from the Late Triassic and the quality of different segments of the fossil record. He holds the Chair in Vertebrate Paleontology at the University of Bristol, UK, in addition to chairing the Masters program in paleobiology at the university.
Your one-stop source for information on evolution. Michael Benton wrote another article, Evidence of Evolutionary Transitions , for this website which explains how fossils support the stages of evolutionary history. Data bases and software for studying the quality of the fossil record. Michael Benton has written over 30 books on dinosaurs and paleobiology.
Accuracy of Fossils and Dating Methods
Two suggested readings are provided — the first for adults, the second for children:. An online directory of dinosaur exhibits fro around the world. Many natural history museums and universities worldwide offer public participation programs in dinosaur events, such as fossil hunting or fossil cataloguing.
No experience needed in most cases! The list is too long to mention here, so a couple of examples are provided to get you going on your search for programs in your area:.
January Fossils provide a record of the history of life. Stratigraphy, the study of rock layers, led to paleontology, the study of fossils. Scientists now use phylogeny, mathematics, and other computations to date fossils. Older fossils cannot be dated by carbon methods and require radiometric dating. The strict rules of the scientific method ensure the accuracy of fossil dating.
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His technique, known as carbon dating, revolutionized the field of archaeology. Now researchers could accurately calculate the age of any object made of organic materials by observing how much of a certain form of carbon remained, and then calculating backwards to determine when the plant or animal that the material came from had died. An isotope is a form of an element with a certain number of neutrons, which are the subatomic particles found in the nucleus of an atom that have no charge.
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While the number of protons and electrons in an atom determine what element it is, the number of neutrons can vary widely between different atoms of the same element. Nearly 99 percent of all carbon on Earth is Carbon, meaning each atom has 12 neutrons in its nucleus. The shirt you're wearing, the carbon dioxide you inhale and the animals and plants you eat are all formed mostly of Carbon Carbon is a stable isotope, meaning its amount in any material remains the same year-after-year, century-after-century.
Libby's groundbreaking radiocarbon dating technique instead looked at a much more rare isotope of carbon: Unlike Carbon, this isotope of carbon is unstable, and its atoms decay into an isotope of nitrogen over a period of thousands of years. New Carbon is produced at a steady rate in Earth's upper atmosphere, however, as the Sun's rays strike nitrogen atoms.
Radiocarbon dating exploits this contrast between a stable and unstable carbon isotope. During its lifetime, a plant is constantly taking in carbon from the atmosphere through photosynthesis. Animals, in turn, consume this carbon when they eat plants, and the carbon spreads through the food cycle.
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This carbon comprises a steady ratio of Carbon and Carbon When these plants and animals die, they cease taking in carbon. From that point forward, the amount of Carbon in materials left over from the plant or animal will decrease over time, while the amount of Carbon will remain unchanged. To radiocarbon date an organic material, a scientist can measure the ratio of remaining Carbon to the unchanged Carbon to see how long it has been since the material's source died. Advancing technology has allowed radiocarbon dating to become accurate to within just a few decades in many cases.
Carbon dating is a brilliant way for archaeologists to take advantage of the natural ways that atoms decay. Unfortunately, humans are on the verge of messing things up. The slow, steady process of Carbon creation in the upper atmosphere has been dwarfed in the past centuries by humans spewing carbon from fossil fuels into the air. Since fossil fuels are millions of years old, they no longer contain any measurable amount of Carbon