Download How Fossils Form worksheets

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Paleontologists study ancient life forms, most of
which are now extinct. They rely on fossils to learn
about life in the past. Fossils are the remains of living things that have been transformed and preserved
sometimes for millions of years.
covered and entombed. When the tree dies it gradually is transformed into coal deposits with the small
amber globules embedding in it. Through erosion or
mining, amber nuggets are sometimes found with tiny
prisoners still perfectly preserved inside.
Most living things are quickly recycled when they
die. Scavengers and bacteria usually consume all but
bones and shells. Even these hard structures are often
crushed or scattered over time. However, there are
several processes that can preserve plants and animals
or their parts.
(distillation)
In this process
of fossilization plant leaves, and some soft body parts
of fish, reptiles, and marine invertebrates decompose
leaving behind only the carbon. This carbon sometimes
creates a detailed impression in the rock outlining the
fossil.
(refrigeration) – Although rare,
sometimes animals are frozen.
This is the best means of preservation, but the animal
must be continually frozen from the time of death until
discovery. This is generally limited to animals from the
last ice age. Mammoth and wooly rhinoceros, found in
Alaskan and Siberian ice, still have flesh, skin, and hair
intact.
(desiccation) – Mummified bodies
of animals, including humans, have
been discovered in arid parts of the world. The soft tissues including skin and organs are preserved for thousands of years if they are completely dried.
Tar pits were formed by crude
oil seeping through fissures in
the earth. The lighter elements of the oil evaporate
leaving thick sticky asphalt. The bodies of animals that
became stuck in the pits have been excellently preserved. Most fossils date between 10 and 40 thousand
years old. Bones, teeth, shells, the exoskeletons of
insects, and even some plant seeds have been pulled
from these asphalt pits. In a similar way fossils have
also been created by peat bogs, paraffin deposits, and
volcanic ash.
Most fossils are found in sedimentary rock. The fossils are made when living things die and get buried by
sediments before the hardest parts of the animal have
a chance to decompose. As sediments accumulate,
pressure causes the sediments to harden into rock.
Fossils form in the rock when groundwater carrying
minerals seeps into the empty places in the cells of
the once living thing and form crystals. These crystals
cause the remains to harden along with the rock that it
is encased in. The shape of the original plant or animal
is preserved in the rock. Sometimes the groundwater
minerals completely replace the remains. This process
is called replacement.
Other important fossils are impressions and molds. These are made
when a hard part, such as a shell, fills up with sediments that harden. Eventually the actual shell dissolves leaving nothing but the sediment mold. These
molds show the body structures of animals and plants
that were once embedded within them.
Sometimes we
don’t find the actual fossilized body of the animal we are looking for.
Insects, spiders, and other small ani- Instead we find trace fossils that can tell us something
mals have been found, nearly perfectly preserved in about the animal and its behavior. Footprints, dropamber. Amber is the hardened sap from ancient trees. pings, egg shells, are not part of the animal, but can
Small creatures that become stuck in the sap become reveal information about its size, diet, life cycle, etc.
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Name
Date
Answer the following questions.
What happens to the soft parts of plants and animals?
Where would you probably find the oldest fossils? Why?
Where would you probably find the youngest fossils? Why?
What kind of animals would leave the best fossil?
What would you be able to infer about the animal that left a fossilized egg shell 10 cm long?