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Fossils
Fossils
(from Classical Latin fossilis; literally, "obtained by digging")[1]
are the preserved remains or traces of animals, plants, and other
organisms from the remote past. The totality of fossils, both discovered
and undiscovered, and their placement in fossiliferous
(fossil-containing) rock formations and sedimentary layers (strata) is
known as the fossil record.
The study of fossils across
geological time, how they were formed, and the evolutionary
relationships between taxa (phylogeny) are some of the most important
functions of the science of paleontology. Such a preserved specimen is
called a "fossil" if it is older than some minimum age, most often the
arbitrary date of 10,000 years.[2] Hence, fossils range in age from the
youngest at the start of the Holocene Epoch to the oldest, chemical
fossils from the Archaean Eon, up to 3.48 billion years old,[3][4][5] or
even older, 4.1 billion years old, according to a 2015 study.[6][7] The
observation that certain fossils were associated with certain rock
strata led early geologists to recognize a geological timescale in the
19th century. The development of radiometric dating techniques in the
early 20th century allowed geologists to determine the numerical or
"absolute" age of the various strata and thereby the included fossils.
Like extant organisms,
fossils vary in size from microscopic, even single bacterial cells[8]
one micrometer in diameter, to gigantic, such as 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. Finally, past life leaves
some markers that cannot be seen but can be detected in the form of
biochemical signals; these are known as chemofossils or biosignatures.
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