Transcript Fossils - MarinScience

Quick-write
• What is a fossil?
Fossils
• Fossils are remains, or evidence, of living
organisms that have been preserved over
millions of years.
Rock fossils
• Remains of living organisms that have been
turned into rock.
• The hard parts of the organism like shells and
bones get buried in sediment.
• Found in layers of sedimentary rock.
Molds and Casts
Petrified wood
Trace fossils
• Evidence the organism existed is preserved in
rock.
• Examples include: footprints, animal homes or
even feces.
Carbon films
• Every living thing contains carbon. Sometimes
when an organism dies the carbon is left
behind on a rock in a visible layer.
Original remains
• These are fossils that are actual bodies or
parts of bodies of the organism. They are
preserved by being sealed inside of a
substance that keeps the organisms from
decaying.
 Amber (resin or tree sap)
Ice (freezes the dead organism)
Tar (sticky, oily substance)
Index Fossils
• Some fossils can be used as index fossils to
provide information about the age of rock
layers. Not all fossils are index fossils.
• An index fossil must have lived:
1. For a relatively short period of time
2. In many places around the world
Index Fossils
• For example: Viviparus is a common river snail
that has only been around since the late Jurassic
period. Rocks containing fossils of Viviparus are
younger than the late Jurassic period.
Relative Age
• Relative age is the age of an event or object in
relation to other events or objects.
• For example I have a younger brother, so you
know he is less than 42 but you don’t know his
exact age.
• If a scientist finds a new kind of fossil in the
same rock as a Viviparus fossil he can
determine the relative age of the new fossil.
Rock layers and relative age
Absolute Age
• To know my brothers absolute age you would
have to know is birthday.
• Scientists can find out the absolute age of
rocks and fossils they use a technique called
radioactive dating.
• Uranium 235 can be used to date igneous rocks
• Carbon 14 is used to date anything that was living.
Radioactive Dating
• When a rock or living organism is formed
some of its elements are unstable.
• Depending upon the element, over a period of
time the element undergoes radio active
decay at a constant rate.
• This decay can be measured in “half-life”
which is the time it takes for half of the
element to decay.
Carbon 14 Decay