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January Fossils provide a record of the history of life. Smith is known as the Father of English Geology. Our understanding of the shape and pattern of the history of life depends on the accuracy of fossils and dating methods. Some critics, particularly religious fundamentalists, argue that neither fossils nor dating can be trusted, and that their interpretations are better. Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.

These skeptics do not provide scientific evidence for their views. Current understanding of the history of life is probably close to the truth because it is based on repeated and careful testing and consideration of data. The rejection of the validity of fossils and of dating by religious fundamentalists creates a problem for them: Millions of fossils have been discovered.

They cannot deny that hundreds of millions of fossils reside in display cases and drawers around the world. Perhaps some would argue that these specimens - huge skeletons of dinosaurs, blocks from ancient shell beds containing hundreds of specimens, delicately preserved fern fronds — have been manufactured by scientists to confuse the public.

This is clearly ludicrous. Some skeptics believe that all fossils are the same age. How exactly they believe that all the dinosaurs, mammoths, early humans, heavily-armored fishes, trilobites, ammonites, and the rest could all live together has never been explained.

Rejecting fossil data cannot be supported by proof. The rejection of dating by religious fundamentalists is easier for them to make, but harder for them to demonstrate. The fossils occur in regular sequences time after time; radioactive decay happens, and repeated cross testing of radiometric dates confirms their validity.

Fossils occur in sequences Fossil sequences were recognized and established in their broad outlines long before Charles Darwin had even thought of evolution.

Early geologists, in the s and s, noticed how fossils seemed to occur in sequences: The first work was done in England and France. Fossil hunting began by accident in England around Around , William Smith in England, who was a canal surveyor, noticed that he could map out great tracts of rocks on the basis of their contained fossils.

The sequences he saw in one part of the country could be correlated matched precisely with the sequences in another. He, and others at the time, had discovered the first principles of stratigraphy — that older rocks lie below younger rocks and that fossils occur in a particular, predictable order.

Stratigraphy, the study of rock layers, led to paleontology, the study of fossils. Then, geologists began to build up the stratigraphic column, the familiar listing of divisions of geological time — Jurassic, Cretaceous, Tertiary, and so on.

Each time unit was characterized by particular fossils. The scheme worked all round the world, without fail. From the s onwards, geologists noted how fossils became more complex through time.

The oldest rocks contained no fossils, then came simple sea creatures, then more complex ones like fishes, then came life on land, then reptiles, then mammals, and finally humans.

Accuracy of the fossils Fossils prove that humans did not exist alongside dinosaurs. Since , paleontologists, or fossil experts, have searched the world for fossils. In the past years they have not found any fossils that Darwin would not have expected. Darwin and his contemporaries could never have imagined the improvements in resolution of stratigraphy that have come since , nor guessed what fossils were to be found in the southern continents, nor predicted the huge increase in the number of amateur and professional paleontologists worldwide.

All these labors have not led to a single unexpected finding such as a human fossil from the time of the dinosaurs, or a Jurassic dinosaur in the same rocks as Silurian trilobites.

Scientists now use phylogeny, mathematics, and other computations to date fossils. Paleontologists now apply sophisticated mathematical techniques to assess the relative quality of particular fossil successions, as well as the entire fossil record. These demonstrate that, of course, we do not know everything and clearly never will , but we know enough.

Today, innovative techniques provide further confirmation and understanding of the history of life. Biologists actually have at their disposal several independent ways of looking at the history of life - not only from the order of fossils in the rocks, but also through phylogenetic trees. Phylogenetic trees are the family trees of particular groups of plants or animals, showing how all the species relate to each other. Phylogenetic trees are drawn up mathematically, using lists of morphological external form or molecular gene sequence characters.

Modern phylogenetic trees have no input from stratigraphy, so they can be used in a broad way to make comparisons between tree shape and stratigraphy. The majority of test cases show good agreement, so the fossil record tells the same story as the molecules enclosed in living organisms. Accuracy of dating Dating in geology may be relative or absolute. Relative dating is done by observing fossils, as described above, and recording which fossil is younger, which is older.

The discovery of means for absolute dating in the early s was a huge advance. The methods are all based on radioactive decay: Fossils may be dated by calculating the rate of decay of certain elements. Certain naturally occurring elements are radioactive, and they decay, or break down, at predictable rates. Chemists measure the half-life of such elements, i. Sometimes, one isotope, or naturally occurring form, of an element decays into another, more stable form of the same element.

By comparing the proportions of parent to daughter element in a rock sample, and knowing the half-life, the age can be calculated. Older fossils cannot be dated by carbon methods and require radiometric dating. Scientists can use different chemicals for absolute dating: The best-known absolute dating technique is carbon dating, which archaeologists prefer to use.

However, the half-life of carbon is only years, so the method cannot be used for materials older than about 70, years. Subtle differences in the relative proportions of the two isotopes can give good dates for rocks of any age. Scientists can check their accuracy by using different isotopes. 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.

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. 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 strict rules of the scientific method ensure the accuracy of fossil dating. Conclusion 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.


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