Montage of multiple fossil taxa. Clockwise from top left: Onychocrinus and Palaeosinopa; bottom row: Gryphaea and Harpactocarcinus

A fossil (from Classical Latin fossilis, lit.'obtained by digging')[1] 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.

Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old.[2] The oldest fossils are around 3.48 billion years old[3][4][5] to 4.1 billion years old.[6][7] 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[8] to dinosaurs and trees, many meters long and weighing many tons. 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.

  1. ^ Oxford English Dictionary. Oxford University Press. Archived from the original on 11 January 2008. Retrieved 17 June 2013.
  2. ^ "theNAT :: San Diego Natural History Museum :: Your Nature Connection in Balboa Park :: Frequently Asked Questions". Archived from the original on 10 May 2012. Retrieved 5 November 2012.
  3. ^ Borenstein, Seth (13 November 2013). "Oldest fossil found: Meet your microbial mom". Associated Press. Archived from the original on 29 June 2015. Retrieved 15 November 2013.
  4. ^ Noffke, Nora; Christian, Daniel; Wacey, David; Hazen, Robert M. (8 November 2013). "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia". Astrobiology. 13 (12): 1103–24. Bibcode:2013AsBio..13.1103N. doi:10.1089/ast.2013.1030. PMC 3870916. PMID 24205812.
  5. ^ Brian Vastag (21 August 2011). "Oldest 'microfossils' raise hopes for life on Mars". The Washington Post. Archived from the original on 19 October 2011. Retrieved 21 August 2011.
    Wade, Nicholas (21 August 2011). "Geological Team Lays Claim to Oldest Known Fossils". The New York Times. Archived from the original on 1 May 2013. Retrieved 21 August 2011.
  6. ^ Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". Excite. Yonkers, NY: Mindspark Interactive Network. Associated Press. Archived from the original on 23 October 2015. Retrieved 20 October 2015.
  7. ^ Bell, Elizabeth A.; Boehnike, Patrick; Harrison, T. Mark; et al. (19 October 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon" (PDF). Proc. Natl. Acad. Sci. U.S.A. 112 (47): 14518–21. Bibcode:2015PNAS..11214518B. doi:10.1073/pnas.1517557112. ISSN 1091-6490. PMC 4664351. PMID 26483481. Archived (PDF) from the original on 6 November 2015. Retrieved 20 October 2015. Early edition, published online before print.
  8. ^ Westall, Frances; et al. (2001). "Early Archean fossil bacteria and biofilms in hydrothermally influenced sediments from the Barberton greenstone belt, South Africa". Precambrian Research. 106 (1–2): 93–116. Bibcode:2001PreR..106...93W. doi:10.1016/S0301-9268(00)00127-3.

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