Why fossils are useful

Fossils also have practical and commercial applications. The oil used in our energy and plastics industries tends to collect in specific types of rock layers. Because fossils can be used to understand the age of different rock layers as described above, studying the fossils that surface when digging oil wells can help workers locate oil and gas reserves reference 2. Perhaps one of the most important functions of fossils from a scientific perspective is that they constitute one line of evidence for understanding evolution.

Fossilization is a relatively rare process. Most organisms are not preserved in the fossil record. Many exceptional deposits of fossils nevertheless provide a surprisingly detailed glimpse into the past and allow scientists to piece together a more complete picture of the history of life on Earth resource 2. Liz Veloz is a writer, scientist and college teacher living in Madison, Wis. The burial process isolates the remains from the biological and physical processes that would otherwise break up or dissolve the body material.

Fossils are more likely to be preserved in marine environments for example, where rapid burial by sediments is possible. Less favourable environments include rocky mountaintops where carcasses decay quickly or few sediments are being deposited to bury them.

The most common method of fossilisation is petrification through a process called permineralisation. After a shell, bone or tooth is buried in sediment, it may be exposed to mineral-rich fluids moving through the porous rock material and becomes filled with preserving minerals such as calcium carbonate or silica.

Petra was the Latin word for rock or stone. This tree stump, found in East Fife, Scotland, is a good example of a petrified tree fossil produced by permineralisation.

Some fossils form when their remains are compressed at depth. A dark imprint of the fossil is produced as a result of high-pressure forces exerted by the weight of overlying sediments and perhaps sea water. Plant leaves and ferns are good examples of fossils produced by compression. This image shows Coniopteris , which is a type of true fern, or pteropsid, fossil from the Jurassic Period.

More about fossil plants. Misleading results can occur if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating A was before B , which is often sufficient for studying evolution. This is difficult for some time periods, however, because of the barriers involved in matching rocks of the same age across continents. Family-tree relationships can help to narrow down the date when lineages first appeared.

It is also possible to estimate how long ago two living branches of a family tree diverged by assuming that DNA mutations accumulate at a constant rate.

For example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different approaches to this method may vary as well. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.

The principle of radiocarbon dating is simple: the rates at which various radioactive elements decay are known, and the ratio of the radioactive element to its decay products shows how long the radioactive element has existed in the rock.

This rate is represented by the half-life, which is the time it takes for half of a sample to decay. Half-life of Carbon : Radiometric dating is a technique used to date materials such as rocks or carbon, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.

The half-life of carbon is 5, years, so carbon dating is only relevant for dating fossils less than 60, years old.

Radioactive elements are common only in rocks with a volcanic origin, so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers. Carbon dating uses the decay of carbon to estimate the age of organic materials, such as wood and leather. Fossils provide evidence that organisms from the past are not the same as those found today, and demonstrate a progression of evolution. Scientists date and categorize fossils to determine when the organisms lived relative to each other.

The resulting fossil record tells the story of the past and shows the evolution of forms over millions of years. Highly detailed fossil records have been recovered for sequences in the evolution of modern horses. The fossil record of horses in North America is especially rich and contains transition fossils: fossils that show intermediate stages between earlier and later forms.

The fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus Eohippus. The first equid fossil was found in the gypsum quarries in Montmartre, Paris in the s. The tooth was sent to the Paris Conservatory, where Georges Cuvier identified it as a browsing equine related to the tapir. His sketch of the entire animal matched later skeletons found at the site. During the H. Beagle survey expedition, Charles Darwin had remarkable success with fossil hunting in Patagonia.

The original sequence of species believed to have evolved into the horse was based on fossils discovered in North America in the s by paleontologist Othniel Charles Marsh. The sequence, from Eohippus to the modern horse Equus , was popularized by Thomas Huxley and became one of the most widely known examples of a clear evolutionary progression. The species depicted are only four from a very diverse lineage that contains many branches, dead ends, and adaptive radiations.

One of the trends, depicted here, is the evolutionary tracking of a drying climate and increase in prairie versus forest habitat reflected in forms that are more adapted to grazing and predator escape through running. Since then, as the number of equid fossils has increased, the actual evolutionary progression from Eohippus to Equus has been discovered to be much more complex and multibranched than was initially supposed.

Detailed fossil information on the rate and distribution of new equid species has also revealed that the progression between species was not as smooth and consistent as was once believed.

Although some transitions were indeed gradual progressions, a number of others were relatively abrupt in geologic time, taking place over only a few million years. The series of fossils tracks the change in anatomy resulting from a gradual drying trend that changed the landscape from a forested habitat to a prairie habitat. Early horse ancestors were originally specialized for tropical forests, while modern horses are now adapted to life on drier land.

Successive fossils show the evolution of teeth shapes and foot and leg anatomy to a grazing habit with adaptations for escaping predators. The horse belongs to the order Perissodactyla odd-toed ungulates , the members of which all share hoofed feet and an odd number of toes on each foot, as well as mobile upper lips and a similar tooth structure.

This means that horses share a common ancestry with tapirs and rhinoceroses. Later species showed gains in size, such as those of Hipparion , which existed from about 23 to 2 million years ago. The fossil record shows several adaptive radiations in the horse lineage, which is now much reduced to only one genus, Equus , with several species. Homology is the relationship between structures or DNA derived from the most recent common ancestor. A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates.

Although these two structures do not look similar or have the same function, genetically, they come from the same structure of the last common ancestor. Homologous traits of organisms are therefore explained by descent from a common ancestor.

If we go all the way back to the beginning of life, all structures are homologous! Homology in the forelimbs of vertebrates : The principle of homology illustrated by the adaptive radiation of the forelimb of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched.

In genetics, homology is measured by comparing protein or DNA sequences. Homologous gene sequences share a high similarity, supporting the hypothesis that they share a common ancestor. Homology can also be partial: new structures can evolve through the combination of developmental pathways or parts of them. As a result, hybrid or mosaic structures can evolve that exhibit partial homologies.

For example, certain compound leaves of flowering plants are partially homologous both to leaves and shoots because they combine some traits of leaves and some of shoots. Homologous sequences are considered paralogous if they were separated by a gene duplication event; if a gene in an organism is duplicated to occupy two different positions in the same genome, then the two copies are paralogous.

A set of sequences that are paralogous are called paralogs of each other. Paralogs typically have the same or similar function, but sometimes do not. It is considered that due to lack of the original selective pressure upon one copy of the duplicated gene, this copy is free to mutate and acquire new functions.

Homology vs. This is because they are similar characteristically and even functionally, but evolved from different ancestral roots. Paralogous genes often belong to the same species, but not always.

For example, the hemoglobin gene of humans and the myoglobin gene of chimpanzees are considered paralogs. This is a common problem in bioinformatics; when genomes of different species have been sequenced and homologous genes have been found, one can not immediately conclude that these genes have the same or similar function, as they could be paralogs whose function has diverged. The opposite of homologous structures are analogous structures, which are physically similar structures between two taxa that evolved separately rather than being present in the last common ancestor.

Bat wings and bird wings evolved independently and are considered analogous structures. Genetically, a bat wing and a bird wing have very little in common; the last common ancestor of bats and birds did not have wings like either bats or birds. Wings evolved independently in each lineage after diverging from ancestors with forelimbs that were not used as wings terrestrial mammals and theropod dinosaurs, respectively.

It is important to distinguish between different hierarchical levels of homology in order to make informative biological comparisons. In the above example, the bird and bat wings are analogous as wings, but homologous as forelimbs because the organ served as a forearm not a wing in the last common ancestor of tetrapods.

Analogy is different than homology. Although analogous characteristics are superficially similar, they are not homologous because they are phylogenetically independent. Analogy is commonly also referred to as homoplasy. Convergent evolution occurs in different species that have evolved similar traits independently of each other. Sometimes, similar phenotypes evolve independently in distantly related species. For example, flight has evolved in both bats and insects, and they both have wings, which are adaptations to flight.

However, the wings of bats and insects have evolved from very different original structures. All fossils are irreplaceable! The National Park Service calls these type of resources "non-renewable. As pieces of once living things, body fossils are evidence of what was living where and when. Trace fossils are valuable because they "animate" the ancient animals or plants by recording a moment of an organism's life when it was still alive.

Identification and classification of body or trace fossils provides a list of ancient plants and animals that lived in a particular place. But without studying the geologic context —such as precise location, type of rock, specific layer, orientation, and other fossils found nearby—there is no story to go along with the remains.

Once a fossil is removed from the ground it cannot be put back, so paleontologists strive to record as much information as possible regarding the context of each fossil. Without such detailed context information, our knowledge of ancient life and landscapes would be greatly reduced and precise connections between parks and other fossil sites would be much more difficult.

The fossil record of the national parks includes billions of individual fossils spanning more than a billion years of earth's history.