The word fossil has its origins in the Latin language, specifically the word 'fossus', which translates to "having been dug up". The word fossil has come to be associated with the study of paleontology, which is the scientific study of fossils and the history of life on Earth.
Fossils come in various sizes, ranging from tiny, one-micrometer bacteria to large creatures like dinosaurs and trees, which can weigh several tons and stretch for meters. Typically, fossils only preserve a part of the organism, such as the mineralized bones and teeth of vertebrates, or the calcareous exoskeletons and chitinous shells of invertebrates. Trace fossils or ichnofossils, which record the organism's activity during its lifetime, such as tracks and coprolites, can also be preserved as fossils. Some fossils are biochemical, known as chemofossils or biosignatures.
How do fossils are formed?
Fossilization is the process by which the remains of dead animals, plants, and other organisms are preserved over time. There are several methods by which fossils are formed, including freezing, drying, encasement in tar or resin, carbonization, permineralization, replacement, and mold and cast formation. Each method involves different physical and chemical processes that can create detailed impressions of organisms and their bodily tissues, or harden their bones and other structures into minerals. While some types of fossils are rare, they provide valuable insights into the past and help scientists to better understand the evolution of life on Earth.
Features of fossils
Fossils are made of rock that replaced the body of the organism or filled in an impression left by the organism.
Fossils are typically made from sedimentary rock rather than igneous or metamorphic rock.
Fossils are formed from plant matter or bones of an organism because soft tissue decays before a fossil is formed.
How fossils are preserved?
In addition to being buried quickly in sediment, there are other ways that fossils can be preserved. For example, in amber, tree resin can trace small organisms, such as insects, and preserve them over millions of years. In oil sands, oil spills, and tar pits, organisms can become trapped and preserved in an oily substance. Similarly, in bogs, acidic water can slow down the decomposition process and preserve organisms, such as plant material, in a mummified state. In ice, freezing temperatures can preserve entire animals, such as woolly mammoths, for thousands of years. These preservation methods can provide scientists with valuable insights into the morphology, behavior, and ecology of organisms from long ago.
Types of preservation
Replacement:
When an organism is buried and becomes fossilized, the original hard parts of the organism can sometimes dissolve away, leaving behind empty spaces in the rock. mineral-rich water can percolate through these empty spaces and deposit new minerals, which gradually fill in the spaces and replace the original material. This process is known as permineralization and often preserves the internal details of the fossil. In some cases, the fossil may also become impregnated or embedded in minerals, which can further enhance its preservation. In other cases, the original material may be completely replaced by a different mineral, a process known as mineralization.
Carbonization/compression:
Another way fossils can be preserved is through the process of compression. When an organism, such as a leaf or fern, is buried in sediment, the weight of the overlying material can cause high pressure that compresses the organic material, expelling volatiles and leaving behind a dark imprint on the rock. This type of fossil preservation is commonly seen in sedimentary rocks.
Exceptional preservation:
This type of preservation occurs in environments where the organism is protected from decay and disintegration, often due to a lack of oxygen. Examples of such environments include amber, oil sands, oil spills, tar pits, glaciers, and bogs. The Burgess Shale in Canada and the Solnhofen Limestone in Germany are two well-known examples of sites where exceptional fossil preservation has occurred.
why do we study fossils?
Fossils are a window into the past that allows us to gain a better understanding of the evolution of life and the impact of changing climates on our planet. They provide evidence of long-extinct species and their relationships with other species. Through the study of fossils, we can trace the evolutionary lineage of modern species and their ancestors. Fossils also serve as a record of past climates, as they can tell us about the types of plants and animals that lived in different regions and their adaptations to environmental conditions. This information can be used to understand the effects of climate change on life on Earth, both in the past and present. By looking at the fossil record, we can gain valuable insights into the ways that life has adapted to changing environmental conditions and the potential impacts of climate change on future biodiversity.
How do we know the age of fossils?
Dating fossils is a crucial aspect of understanding the history of life on Earth. There are two main methods used to age-date fossils: relative dating and absolute dating. Relative dating involves comparing the ages of two fossils to determine which is older and which is younger. Fossils are commonly found in sedimentary rock, which forms in layers. The layers at the bottom are the oldest, while those on top are the youngest. By studying the order of these layers, scientists can determine the relative ages of fossils found in them.
Absolute dating, on the other hand, allows scientists to determine the exact age of a fossil. This is done by measuring the amount of radioactive decay that has occurred in certain elements found in rocks. These unstable elements decay into stable elements at a constant rate, which is like a clock that starts running as soon as the rock is formed. By measuring the ratio of the parent element to the daughter element, scientists can calculate the age of a rock and the fossils found within it. This method provides a more precise age determination than relative dating and allows scientists to reconstruct the timeline of evolution with greater accuracy. By using both relative and absolute dating methods, scientists can piece together the complex history of life on our plane.
fossils used for dating of rock
Fossils can be used to determine the relative age of rocks, which helps understand the geological history of an area. The basic idea is that the more primitive an organism is, the older the rock that contains it is likely to be. For example, if a rock contains fossils of single-celled organisms, it is likely to be older than a rock that contains fossils of multi-celled organisms. Similarly, if a rock contains fossils that are 425 million years old, it is likely to be older than a rock that contains fossils that are 400 million years old. In addition, the rock that contains the fossils must be older than the fossils themselves for them to be preserved in that rock. By studying the fossils found in rocks, scientists can piece together the relative chronology of geological events, which can shed light on the history of life on Earth.