Fossil

FOSSIL is a standard protocol for allowing serial communication for telecommunications programs under MS-DOS compatible operating systems. FOSSIL is an acronym for Fido Opus SEAdog Standard Interface Layer. Fido refers to FidoNet, Opus refers to Opus-CBCS BBS, and SEAdog refers to a Fidonet compatible mailer. The standards document that defines the FOSSIL protocol is maintained by the Fidonet Technical Standards Committee.

, Palaeosinopa, Gryphaea, and Harpactocarcinus A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record. Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth, and it can fill gaps in our understanding of the sequence of evolution on earth. Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are sometimes considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration. Fossils vary in size from one-micrometre (1 μm) bacteria to dinosaurs and trees, many meters long and weighing many tons. The largest presently known is a Sequoia sp. measuring in length at Coaldale, Nevada. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils or ichnofossils, as opposed to body fossils. Some fossils are biochemical and are called chemofossils or biosignatures.

Limitations

Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, only a small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which are never guaranteed to demonstrate a convenient half-way point. The fossil record is strongly biased toward organisms with hard parts, leaving most groups of soft-bodied organisms with little to no presence. It is replete with mollusks, vertebrates, echinoderms, brachiopods, and some groups of arthropods.

Phosphatization

Phosphatization refers to a process of fossilization where organic matter is replaced by abundant calcium-phosphate minerals. The produced fossils tend to be particularly dense and have a dark coloration that ranges from dark orange to black.

Pyritization

This fossil preservation involves the elements sulfur and iron. Organisms may become pyritized when they are in marine sediments saturated with iron sulfides. As organic matter decays, it releases sulfide which reacts with dissolved iron in the surrounding waters, forming pyrite. Pyrite replaces carbonate shell material due to an undersaturation of carbonate in the surrounding waters. Some plants become pyritized when they are in a clay terrain, but to a lesser extent than in a marine environment. Some pyritized fossils include Precambrian microfossils, marine arthropods, and plants.

Silicification

In silicification, the precipitation of silica from saturated water bodies is responsible for the fossil's formation and preservation. The mineral-laden water permeates the pores and cells of some dead organism, where it becomes a gel. Over time, the gel will dehydrate, forming a silica-rich crystal structure, which can be expressed in the form of quartz, chalcedony, agate, opal, among others, with the shape of the original remain.

Derived or reworked

plesiosaur vertebral centrum found in the Lower Cretaceous Faringdon Sponge Gravels in Faringdon, England. An example of a remanié fossil. A derived, reworked or is a fossil found in rock that accumulated significantly later than when the fossilized animal or plant died. Reworked fossils are created by erosion exhuming (freeing) fossils from the rock formation in which they were originally deposited and redepositing them in a younger sedimentary deposit. "Grand Canyon cliff collapse reveals 313 million-year-old fossil footprints" 21 August 2020, CNN "Hints of fossil DNA discovered in dinosaur skull" by Michael Greshko, 3 March 2020, National Geographic "Fossils for Kids | Learn all about how fossils are formed, the types of fossils and more!" Video (2:23), 27 January 2020, Clarendon Learning "Fossil & their formation" Video (9:55), 15 November 2019, Khan Academy "How are dinosaur fossils formed? by Lisa Hendry, Natural History Museum, London "Fossils 101" Video (4:27), 22 August 2019, National Geographic "How to Spot the Fossils Hiding in Plain Sight" by Jessica Leigh Hester, 23 February 2018, Atlas Obscura "It's extremely hard to become a fossil" , by Olivia Judson, 30 December 2008, The New York Times "Bones Are Not the Only Fossils" , by Olivia Judson, 4 March 2008, The New York Times

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