Transcript EarthsPastPowerpoint..

Earth’s Past
Fossils are traces or remnants of past
life. Many fossils are found in rock.
Rocks, fossils, and other natural
evidence provide information about
how Earth and life on Earth have
changed over time.
original remains
A fossil that is the actual body or body parts of an
organism. There are 3 different substances
original remains are found are the following:
1. 1. Ice- Ice preserves remains (Mammoth)
2. 2. Amber- Resin from tree hardened and
preserves remains (insects)
3. 3.Tar- Pools of tar preserve remains (Sabertoothed cats)
Fossils in Rocks
•
These fossils are impressions or traces
made of rock and provide indirect
evidence that the organisms were there.
There are 4 types of fossils in rocks:
1. Mold and Cast
2. Petrified wood
3. Carbon Films
4. Trace fossils
Process and Example of Mold and
Cast
1. Organism dies and falls into soft
sediment.
2. Over time, the sediment becomes rock
and the organism decays, leaving a mold.
3. Minerals fill the mold and make a cast of
the organism.
Example- Clams, snails
A mold and cast fossil is formed when minerals
take the shape of a decayed organism.
Mold and Cast Fossil
Petrified Wood
• The stone fossil of a tree is called petrified
wood.
Process - A fallen tree can be covered with
sediment. Over time, water passes
through the sediments and into the trees
cells. Minerals that are carried in the water
take the place of the cells, producing a
stone likeness of the tree.
Example- petrified forest
Petrified Wood
Carbon Films
• Carbon is an element that is found in
everything living.
• Process- Sometimes when dead plant or
animal decays, its carbon is left behind on
a visible layer.
• Example- moth 10 million years old
Carbon Film
Trace Fossils
• Trace fossil is a fossil that demonstrates that a
particular living organism existed.
• Process of how the trace fossils are preserved is
when weather changes drastically and causes
weathering and erosion to occur which
preserves events that occurred prior to the
change.
• Example of Trace fossils include preserved
footprints, trails, animal holes, and even feces.
Trace Fossils
Scientists combine information about the
relative and absolute ages of rocks and
fossils to construct a timeline of Earth.
relative age
The age of an event or object in relation to
other events or objects
(sedimentary rock only)
absolute age
The actual age in years of an event or
object. (igneous rock- radioactive dating
and once living organisms-carbon dating).
index fossil
A fossil of an organism that was common,
lived in many areas, and existed only
during a certain span of time. Index fossils
are used to help determine the age of rock
layers.
half-life
• The length of time it takes for half of the
atoms in a sample of a radioactive
element to decay into atoms of another
element
Sedimentary rock
layers show the order
in which rocks formed.
The order of the layers
is used to determine
the relative ages of
fossils found in the
rock.
Radioactive dating can
be used to determine
the absolute age of
igneous rock.