Skeleton that the bird-like specimen (Aurornis xui) uncovered in Yizhou Fossil & Geology Park, China.(Image credit: Thierry Hubin/IRSNB)
When animals, plants and also other biology die, they frequently decay completely. But sometimes, as soon as the problems are simply right, they"re preserved as fossils.

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Several various physical and also chemical processes createfossils, according to the brand-new York State geology Survey.

Freezing, drying and also encasement, such together in tar or resin, can create whole-body fossils that keep bodily tissues. This fossils stand for the organisms together they were when living, however these varieties of fossils are very rare.

Most organisms become fossils once they"re adjusted through assorted other means.


The heat and also pressure from being hidden in sediment can sometimes cause the tissues of biology — including plant leaves and the soft body components of fish, reptiles and also marine invertebrates — to relax hydrogen and oxygen, leaving behind a residue ofcarbon.


This procedure — i beg your pardon is dubbed carbonization, or distillation — returns a in-depth carbon impression of the dead organism in sedimentary rock.

The many common technique of fossilization is called permineralization, or petrification. After an organism"s soft tissuesdecay in sediment, the hard parts — particularly the bones — are left behind.

Water seeps into the remains, and also minerals liquified in the water seep into the spaces in ~ the remains, where they form crystals. This crystallized minerals cause the remains to harden along with the encasingsedimentary rock.


In an additional fossilization process, referred to as replacement, the minerals in groundwater replace the mineral that consist of the bodily remains after the water completely dissolves the original tough parts the the organism.

Fossils also form from molds and also casts. If one organism completely dissolves in sedimentary rock, it have the right to leave an impression that its exterior in the rock, dubbed an exterior mold. If the mold it s okay filled with various other minerals, it i do not care a cast.

An inner mold develops when sediments or minerals to fill the inner cavity, such together a shell or skull, of one organism, and also the stays dissolve.

Organic remnants

In current years, researcher have discovered that some fossils aren"t just made of minerals. Fossil analyses have shown, for instance, that some retain organic materialdated come the Cretaceous, a period that lasted indigenous 65.5 million come 145.5 million years ago, and the Jurassic period, i m sorry lasted from 145.5 million to 199.6 million year ago

Tests suggest that this organic materials belong to dinosaurs due to the fact that they match details proteins from birds, which developed from dinosaurs.

"It supplied to be that no one believed it was feasible for any endogenous material — material that comes from the pet — might be left behind after the fossilization process," stated Ken Lacovara, the dean of the institution of Earth and also Environment at Rowan college in brand-new Jersey. " that"s no really the case."

It"s unclear just how the organic material is preserved, but iron might assist the proteins end up being cross-linked and unrecognizable, or unavailable to the bacteria that would certainly otherwise consume them, Lacovara said. (Formaldehyde works in a comparable way, cross-linking the amino mountain that comprise proteins, do them an ext resistant to decay, mary Schweitzer, a molecular paleontologist at phibìc Carolina State University, told Live Science.)

Another idea is "microbial masonry," Lacovara said. "It"s feasible that the bacteria that at first chomped with the tissue space secreting minerals together a rubbish product that then hermetically seal a small bit that what continues to be behind," almost like a stone mason sealing off a structure, the told Live Science.

Moreover, sandstone — rock made of sand-size seed of minerals, sediments or inorganic material — appears to be the best form of setting for preserving organic material in fossils.

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"Sandstone is like a bunch that volleyballs sit on optimal of each various other with large interstitial areas between them," Lacovara said. "So that seems prefer rapid decay can promote the preservation process. Maybe we require the bacteria to obtain through fast and to chomp with the sediment so that they can sequester several of in the process."

Additional reporting by employee Writer Laura Geggel.

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Joseph Bennington-Castro is a Hawaii-based contributing writer for Live Science and Space.com. The holds a master"s level in science journalism from new York University, and also a bachelor"s degree in physics indigenous the university of Hawaii. His work-related covers all locations of science, indigenous the quirky mating behaviors of different animals, to the drug and alcohol behavior of old cultures, to brand-new advances in solar cabinet technology. ~ above a an ext personal note, Joseph has had actually a near-obsession with video clip games because that as lengthy as he have the right to remember, and also is probably playing a game at this an extremely moment.