Fossils 101 | National Geographic


(gentle music) – [Narrator] Like buried treasure, they lie hidden from sight. Echoes of an ancient
past, they whisper secrets and tell tales once lost to time. Fossils are remnants or
impressions of ancient organisms that are naturally preserved in stone. While there are hundreds of fossil types, they are often grouped
into two major categories, body fossils, which are
the preserved remains of plants and animals, and trace fossils, which are records of an animal’s behavior, such as footprints. Together, they form the fossil record, a primary account that tells the story of life on Earth through stone. Fossilization or the process of preserving organisms in stone, can
occur in countless ways. These methods are largely grouped depending on whether the organisms are altered during the
fossilization process. Fossilization that does
not alter a specimen can help to preserve its
original form and texture. Among many methods, this
group includes organisms that have been frozen, preserved in tar pits, and mummified. One special case involves
trapping organisms, oftentimes insects, in amber. This process begins when
an organism is covered in tree sap. The sap or resin forms a protective seal around the entrapped organism. Over time, the soft resin hardens and turns into amber with the organism suspended within. This process creates a
biologically inert tomb for the organism,
allowing its soft tissues to be remarkably preserved. Other fossilization
methods change the specimen as it is being preserved. For instance, carbonization
transforms soft tissues into thin black films of carbon. In fact, countless layers
of carbonized plant material create a well known fossil fuel, coal. But one of the most common
types of fossilization that changes a specimen is
called permineralization. Permineralization begins
when minerals from water or the ground enter
the pores of dead plant or animal material. Over time, the minerals attach themselves, clinging onto cellular walls and building a crystalline
network in the empty cavities. This mineralization hardens the bone and turns it into stone, thereby preserving its original
structure in fossil form. When conditions are right, fossilization can preserve
crucial information about an organism. Permineralized wood often
contains enough information to identify its tree genus and sometimes its species. Insects encased in amber
have been so well preserved that their genetic material was extracted and partially sequenced. And footprints left
behind by ancient hominids help paint a picture of what life was like for early human ancestors
millions of years ago. With every fossil uncovered, the planet’s ancient past becomes clearer, helping shape our understanding
of our world today. (gentle music)

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