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

You are watching: Fossil formed when an outline of the original organism is formed from left-over carbon


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

Freezing, drying and also encasement, such as in tar or resin, can produce whole-body fossils that preserve bodily tissues. This fossils represent the organisms together they were as soon as living, but these varieties of fossils are really rare.


The heat and also pressure indigenous being hidden in sediment can sometimes reason the organization of organisms — consisting of plant leaves and the soft body components of fish, reptiles and marine invertebrates — to release hydrogen and also oxygen, leaving behind a residue ofcarbon.


This process — which is dubbed carbonization, or distillation — yields a in-depth carbon impression of the dead organism in sedimentary rock.

The many common an approach of fossilization is referred to as permineralization, or petrification. ~ an organism"s soft tissuesdecay in sediment, the difficult parts — specifically the skeleton — are left behind.

Water seeps right into the remains, and also minerals dissolved in the water seep into the spaces within the remains, wherein they kind crystals. This crystallized minerals cause the remains to harden along with the encasingsedimentary rock.

In an additional fossilization process, called replacement, the minerals in groundwater change the minerals that comprise the bodily stays after the water completely dissolves the original hard parts of the organism.

Fossils also kind from molds and also casts. If an organism totally dissolves in sedimentary rock, it deserve to leave one impression that its exterior in the rock, dubbed an exterior mold. If that mold it s okay filled with other minerals, it becomes a cast.

An inner mold creates when sediments or minerals to fill the internal cavity, such as a covering or skull, of an organism, and the stays dissolve.

Organic remnants

In recent years, researchers have found that part fossils aren"t just made the minerals. Fossil analyses have actually shown, because that instance, that some retain essential materialdated to the Cretaceous, a duration that lasted native 65.5 million to 145.5 million years ago, and also the Jurassic period, i m sorry lasted indigenous 145.5 million to 199.6 million years ago

Tests imply that these organic materials belong come dinosaurs because they match details proteins indigenous birds, which progressed from dinosaurs.

"It provided to be the no one believed it was possible for any type of endogenous material — product that comes from the pet — could be left behind after the fossilization process," claimed Ken Lacovara, the dean the the college of Earth and also Environment in ~ Rowan university in new Jersey. " that"s no really the case."

It"s unclear how the organic product is preserved, yet iron might assist the proteins come to be cross-linked and unrecognizable, or unavailable to the bacteria that would otherwise consume them, Lacovara said. (Formaldehyde functions in a comparable way, cross-linking the amino acids that comprise proteins, do them more resistant to decay, mar Schweitzer, a molecular paleontologist at phibìc Carolina State University, called Live Science.)

Another idea is "microbial masonry," Lacovara said. "It"s feasible that the bacteria that initially chomped through the tissue are secreting minerals together a waste product that then hermetically seal a little bit of what continues to be behind," virtually like a stone mason sealing off a structure, the told Live Science.

Moreover, sandstone — absent made the sand-size grains of minerals, sediments or inorganic material — appears to it is in the best kind of environment for preserving organic product in fossils.

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"Sandstone is prefer a bunch of volleyballs sitting on height of each various other with large interstitial locations between them," Lacovara said. "So it seems like rapid decay could promote the conservation process. Possibly we need the bacteria to obtain through fast and also to chomp with the sediment so that they can sequester few of in the process."

Additional reporting by staff Writer Laura Geggel.

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Joseph Bennington-Castro is a Hawaii-based contributing writer because that Live Science and Space.com. He holds a master"s level in science journalism from new York University, and also a bachelor"s level in physics from the college of Hawaii. His work covers all locations of science, indigenous the quirky mating habits of different animals, come the drug and alcohol behavior of old cultures, to brand-new advances in solar cell technology. ~ above a much more personal note, Joseph has had a near-obsession with video games for as lengthy as he deserve to remember, and also is most likely playing a game at this really moment.