Page 73 - The Restless Earth Fossils

72 Fossils

recording and extracting Fossil Finds
Scientists must know all the details about a fossil’s origin in
order to successfully “read” the past. A variety of books, like The
Practical Paleontologist by Steve Parker, describe some of the basic
techniques.
Sketch maps that show the various layers, or horizons, at a
site allow scientists to give fossils an accurate date based on com-
parisons with other documented sites. They look for rock features
like grain size, how crumbly the layer is, the kinds of fossils in
place, if any, and color of the rock. Sketch maps include measure-
ments recording the depths of each layer. Photographs can be
useful, especially if they show easily recognized landmarks. Field
notebooks should also contain frame numbers and a description
of the fossil captured in each photograph to easily identify them
later.
Large fossil sites may be staked out using the grid method.
Field crews place pegs at one-yard (or one-meter) intervals and
connect them with string. A wooden frame that measures one-
yard (or one meter) square is similarly divided into squares mea-
suring 4 inches (or 10 cm) on a side. Someone moves this frame
over each square in sequence and records on graph paper the fos-
sils or fragments found in each smaller square. This process may
have to be repeated at various depths as people remove rock from
each square, so a big excavation can take a long time.
Extracting fossils can be as simple as picking them off the
ground or as difficult as hauling off blocks of stone weighing
tons. When blocks of limestone contain many fossils, a paleon-
tologist can break off a chunk and treat it with dilute acids like
muriatic acid (HCl) or acetic acid (vinegar). The preparer alter-
nates acid baths with careful washing of the specimen and treat-
ment with chemical hardeners that firm up the fossil as matrix
dissolves away. Rock hammers and chisels, when used carefully
by those with some experience, can reduce the size of a rock in
the field. Huge fossil bones become exposed on one side and then
covered by layers of burlap dipped in plaster of Paris. Field work-
ers then undercut a hunk of stone containing the entire bone or

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