Transcript History of Life

History of Life
Section 14.1
Reminder:
• Don’t forget to bring your 100 pennies per
pair.
Early History of Earth
What was it like?
Scientists suggest that it
was…
• Very hot
• Atmosphere
contained little
Oxygen.
• Had a lot of water
vapor, carbon dioxide
and nitrogen.
• Evidence suggests that the earth is
4.6 billion years old.
• However, it is possible that life
originated between 3.9 and 3.5 billion
years ago.
Do Scientists Know for Sure?
No.
Why Not?
What do Scientists Use to Study
the history of earth?
• Oldest rocks on the earth formed
3.9 billion years ago.
• Importance Source of Information
about the diversity that existed on
the planet.
Scientists can’t just look at the
organisms alive today to learn
about biodiversity.
About 99% of species that have
ever lived are extinct.
Fossils Provide Clues to the Past
A fossil is evidence of an organism
that lived long ago.
Types of Fossils
• Trace fossils
• Casts
• Petrified Fossils
• Imprints
• Amber-preserved and frozen fossils
• Molds
Trace fossils
A trace fossil is the
marking left by
an animal and
may include a
footprint, a trail,
and a burrow.
Casts
Mesosaurus
When minerals in
rocks fill a space
left by a decayed
organism, they
make a replica,
or cast, of the
organism.
Petrified Fossils
Minerals
sometimes
penetrate and
replace the hard
parts of an
organism,
producing copies
of them.
Imprints
A thin object, such
as a leaf, that
falls into
sediment can
leave an imprint
when the
sediment
hardens into
rock.
Molds
A mold forms
when an
organism is
buried in the
sediment and
then decays,
leaving an empty
space.
Trilobite
Amber-Preserved and Frozen
At times, an entire
organism was
quickly trapped
in ice or tree sap
that hardened
into amber.
What is the limitation of fossils?
Fossils are only snapshots of
history.
The information is limited.
For example,
what can
you tell from
this picture?
Paleontologists
• Paleontologists-scientists who study
ancient life.
• Like detectives of the past.
Suppose….
...paleontologists were to uncover
rocks that had a layer with
fossilized ferns and then the layer
above it had the fossilized
remains of fish?
What would they be able to
deduce?
Paleontologists use different
clues to discover things about
the organisms and climate of
the area
Clues like condition, position,
and location of rocks and
fossils.
Fossils are usually found in
sedimentary rock.
This is because of the
differences in how rocks are
formed.
How fossils are formed
• An organism
dies.
How fossils are formed.
• The remains are
covered by
sediment.
How Fossils are Formed.
• Hard parts get
replaced by
minerals in the
soil and form
into rock by
compression.
How Fossils are Formed.
• Earth
Movements or
erosion may
expose the fossil
millions of years
later.
How do we determine the age of a
fossil?
Two methods:
Relative Dating
Radiometric Dating
Relative Dating
• Dating the past by how it was laid down.
• Oldest is generally on the bottom.
• Can determine order of species.
Radiometric Dating
• Use to determine the actual age
of an organism.
• Radioactive isotopes decay at a
specific rate. Knowing this rate,
scientists are able to discover the
approximate age of a certain rock
or fossil.