Transcript Fossils - Effingham County Schools

Fossils
How to tell time with rocks
Looking at Fossils
►A
fossil is any naturally preserved evidence
of life.
Mineralization / Petrification
Fossil
► Organisms
can also
be preserved by
mineralization
(petrified), a
process in which
minerals fill in pore
spaces of an
organism’s tissues.
Fossils in Amber
► When
tree sap hardens, an insect may be
preserved inside. Hardened tree sap is
called amber. Some of our best insect fossils
are found in amber.
Mummification
► When
organisms die in dry places (such as
deserts), they can sometimes dry out so
fast that there isn’t enough time for their
soft parts to decay.
Frozen Fossils
► Frozen
specimens
► Found in
ancient
glaciers.
Trace Fossils
► Any
naturally preserved evidence of an
animal’s activity is called a trace fossil.
Molds and Casts
►A
mold is a cavity in the ground or rock
where a plant or animal was buried.
► A cast is an object created when sediment
fills a mold and becomes rock.
Fossils Show
Changes in Environments
► Fossils
can reveal changes that have
occurred in parts of the Earth.
► How did sea creatures
end up on dry land?
Fossils Show
Changes in Life
► Older
rock layers contain
organisms different from
those found in younger
rock layers.
► Life forms have changed
over millions of years.
For example, giant sea
reptiles came before
giant land dinosaurs.
Mammals arrived last!
►A
fossil is a remnant or trace of an organism
from the past, such as a skeleton or leaf
imprint.
► Fossils
are embedded and preserved in the
earth's crust.
►A
Trace Fossil is a fossil of a footprint, trail,
burrow, or other trace of an animal rather
than of the animal itself
►
A footprint of an ancient animal in a rock is
called a trace fossil.
► Large
animals occasionally became trapped
in tar and become a fossil.
► Fossils,
the
remains of
organisms
preserved in
sedimentary
rocks, are part of
the evidence
scientists use to
infer changing
conditions at the
Earth’s surface
through time.
► Oil
and Natural Gas are formed from ocean
plankton that died millions of years ago.
► Coal,
Natural Gas, and Oil are all examples
of fossil fuels.
► Petrified
wood is a fossil.
►
► Petrified
wood forms when water with
natural minerals slowly fills the pores of
wood. Over thousands of years the wood
slowly decomposes leaving behind the
minerals from the water. The minerals
harden and form a rock that looks exactly
like the original wood.
►
How much wood is actually located in
petrified wood? 0%.
► The
geologic
column is how
geologists
have
organized the
entire history
of the Earth in
chronological
order.
ROCKS TELL A STORY
► Rocks
can tell where they
were made and when
► Sedimentary
rocks can
have fossils in them
► Rocks
can tell when mass
extinctions happened
LAW OF SUPERPOSITION
For undisturbed rocks, the oldest layer is on
the bottom and the youngest is on top (Supai
is oldest)
► Superposition
states that older layers of
rock are below younger layers of rock.
LAW OF SUCCESSION
► Fossils
are found in a predictable sequence
► Fossils in rock B are older then fossils in rock A
RELATIVE DATING & AGE
►
Relative Dating:
putting rocks and
geological events in
correct chronological
order
►
Relative Age: how old
something is in
comparison to
something else
►
HOW?
 Use of sedimentary rocks
 Use of fossils
 Study of strata
Absolute Dating
►
►
Absolute dating is a
process that
establishes the precise
age of an object, fossil,
or rock layer by
determining the
number of years it has
existed.
Radiometric dating
is how absolute dating
is accomplished.
Scientists determine
the actual age of a
fossil or rock by
measuring the decay of
certain atoms.
► Radiometric
dating is how geologists
determine the age of rocks by measuring
the decay of atoms.
► Radiometric
dating is the most accurate way
to date rocks and fossils.
What kind of rocks
are these fossils in?
Which layer is
oldest?
Which layer is
youngest?
How do you know?