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.
There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration.įossils vary in size from one- micrometre (1 µm) bacteria to dinosaurs and trees, many meters long and weighing many tons. 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. 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 oldest fossils are around 3.48 billion years old to 4.1 billion years old. Specimens are usually considered to be fossils if they are over 10,000 years old. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. The totality of fossils is known as the fossil record.
Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. A fossil (from Classical Latin: fossilis, literally 'obtained by digging') is any preserved remains, impression, or trace of any once-living thing from a past geological age.
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