NEW YORK FOSSILS

What is a fossil?

Fossils represent the preserved remains of life of the past. The word "fossil" comes from the Latin word "fossilis" which means "dug up"; remains must be buried to become preserved. The study of fossils is paleontology.    

Fossils come in two major types: body fossils and trace fossils.  Body fossils  represent an actual body part (rarely the entire body).  Usually an organism dies,  but a body part may  have been discarded (a molt of an  arthropod, a shed tooth of a shark, for example).  Trace fossils are evidence of  the activity of an organism, for example, burrows left by worms or an organism's footprints.

How are fossils preserved?

The fossil record is biased, especially in the types of organisms preserved. When an organism dies, bacteria act to decompose the soft parts.   The only parts that usually survive are skeletal structures, if present, especially  if they are mineralized skeletons ("hard parts") impregnated with crystals of calcium carbonate (calcite or aragonite), calcium phosphate (apatite), or silica. Animals with mineralized  skeletons include corals, brachiopods,  bryozoans, mollusks, echinoderms, and many chordates.  It is no wonder that the fossil  record is biased toward these  groups, while those lacking a mineralized skeleton, such as worms, jellyfish, and  insects, are poorly represented.

Once they are successfully buried, remains usually are altered during or after  the fossilization process.   Soft parts may be preserved under  unusual circumstances, such as burial in an anoxic environment, surrounding  them with an "air-tight" material such as amber or tar,  or even freezing.  Organic compounds may volatize to leave thin  films of carbon, a process  called carbonization.

Hard parts may be preserved in their original unaltered state, but this becomes rarer  the further back in time one  goes.  Minerals such as calcite and (especially) aragonite are prone to recrystallization, so even though shell material may be preserved, the original crystal arrangement  is often destroyed.   Hard parts may be replaced by quartz (silica) or other minerals.   Porous materials (commonly bone or wood) may  be preserved by a process called permineralization, with individual void spaces  filled by minerals such as silica to preserve minute detail. Hard parts may also be buried in sediment that then becomes firm, only to have them dissolve away to leave  a cavity or mold that may later be filled by mineral matter to form a cast. If the inside of a shell is filled with sediment or minerals and the shell is then dissolved away, an internal  mold, or steinkern, is formed that has  on its outer surface the details of the inside surface of the shell.

The scientific value of fossils

Once fossils are found, they are useful in several types of investigation.  Biostratigraphy uses fossils to assign  relative ages to rocks, based on the idea that species evolved through time so that a given species lived only during a  relatively brief interval of geologic time.  Oil companies need people who can date rocks using fossils (usually using  microfossils since they are abundant and easily recovered from drill holes).  Paleoecology is the study of the interactions  between fossil species and each other and the environment.  It is valuable in interpreting what conditions were like in the  past, where land and sea was, and even where to look for fossil fuels.  Ancient environment interpretation is also aided by  taphonomy, the study of the preservation of fossils.  The state of preservation reflects environmental conditions and  processes that acted on the remains in the environment both before and after burial.