Transcript fossil - Northwest ISD Moodle

Evolutionary
Evidence
Part 1: Fossil Record
Bellringer
• In your science journal, write and
respond to the following question:
–How do scientists learn about
organisms of the past when
studying fossils?
Objectives:
• I can define fossil and explain why fossils are
important pieces of evolutionary evidence.
• I can identify the different types of fossils.
• I can explain how fossils are formed.
• I can describe two methods to determine the age
of fossils.
• I can explain why the fossil record is incomplete
• I can analyze components of the fossil record
and determine the sequence in which the
organisms appear.
What are the different types of evidence used
to support the evolutionary theory?
There are several places we
can see indirect evidence of
evolution/evolutionary
relationships:
 fossils,
 biogeography,
 similarities in
anatomy,
 biochemistry/DNA,
 and embryology.
What is a fossil and why is it
important?
• A fossil is any preserved evidence of an
organism that lived long ago found in the
Earth’s rocks.
• Plants, animals, and bacteria can form
fossils.
• The fossil record shows that some species
from long ago are extinct today. Other
species alive today are similar to those in
fossils.
Why does the fossil record not provide as
much evidence as the other components of
evolutionary evidence?
• There are missing links even in fossil
record.
• Approximately 99% of the species that
have ever lived are now extinct, but only a
tiny percentage of that was preserved as
fossils.
• Most organisms decompose before they
have the chance to become fossilized.
What are the different types of
fossils?
TYPES OF FOSSILS
Fossils Types
Formation
A trace fossil is any indirect evidence
Trace fossils
Casts
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
left by a decayed organism, they make
a replica, or cast, of the organism.
A mold forms when an organism is
Molds
Petrified
fossils
Amber-Preserved
or
frozen fossils
buried in sediment and then decays,
leaving an empty space.
Petrified-minerals sometimes penetrate
and replace the hard parts of an organism
At times, an entire organism was
quickly trapped in ice or tree sap that
hardened into amber.
What are the different types of
fossils?
• Trace fossils – footprints, burrows, feces
• Molds and casts – impressions or a mold filled
with sediment
• Replacement – original material replaced with
mineral crystals
• Petrified or Permineralized – empty pores are
filled in by minerals
• Amber – tree sap preserved
• Original material – mummification or freezing
What are transitional fossils
and why are they important?
• Charles Darwin predicted that scientists
would find fossils that would show
organisms that were intermediates
between different species.
• Scientists today have found thousands of
transitional fossils that contain features
shared by different species.
• Scientists have found intermediate species
for the evolution of mollusks, modern
horses, whales, and humans.
What are the classes of
transitional fossils?
• 2 major classes of transitional fossils:
– Derived traits
– Ancestral traits
• Derived traits are newly evolved features,
such as feathers, that do not appear in the
fossils of common ancestors.
• Ancestral traits are more primitive
features, such as teeth and tails, that do
appear in ancestral forms.
Who studies fossils?
• Paleontologists, scientists who study ancient life, are
like detectives who use fossils to understand events
that happened long ago.
• They use fossils to determine the kinds of organisms
that lived during the past and sometimes to learn
about their behavior.
How are fossils formed?
• For fossils to form, organisms
usually have to be buried in mud,
sand, or clay soon after they die.
• Fossils are not usually found in other types of rock because of the ways
those rocks
form.
• Most
fossils
are found in sedimentary rocks.
rocksthe
form
at relatively
low temperatures
and
pressures
• These
For example,
conditions
under which
metamorphic rocks
form
often
that
may
damage
to the
organism.
destroy
anyprevent
fossils that
were in the
original
sedimentary rock.
How are fossils formed?
• Fossils do not form in igneous or
metamorphic rock; they will not survive the
heat or pressure involved in the formation
of these kinds of rocks.
• Fossils are formed in sedimentary rock.
Why is it that not all organisms become
fossils?
• Few organisms become fossilized because, without
burial, bacteria and fungi immediately decompose
their dead bodies.
• Occasionally, however, organisms do become fossils
in a process that usually takes many years.
“How fossils form”
Right click the above
link and open the
hyperlink to look at an
interactive lesson on
fossil formation
What are the methods in which scientists
use to determine the age of a fossil?
• Relative dating
• This method is used to
determine the age of rocks
by comparing them with
those in other layers
• This method basically
indicates that the fossils
found closer to the surface
are younger, and the fossils
found in deeper strata are
• This method does not
more primitive (older)(in
give a specific age of
undisturbed ground)
the fossil or rock.
What are the methods in which scientists use to determine the age of a fossil?
RELATIVE DATING
What are the methods in which scientists
use to determine the age of a fossil?
• Using this principle of relative dating,
scientists can determine relative age and
the order of appearance of the species
that are preserved as fossils in the layers.
• The law of superposition states that
younger layers of rock are deposited on
top of older layers.
What are the methods in which scientists use
to determine the age of a fossil?
• Radiometric dating
• This method uses the decay of radioactive isotopes of
atoms to measure the absolute age of a rock.
• To find the specific ages of rocks, scientists use
absolute dating, also called Radiometric Dating.
• As specific atoms decay they emit radiation and lose
electrons, which causes them to turn into a different
element.
• So- these atoms change from one thing into
something else over time- and they do this at a
constant rate.
What are the methods in which scientists use
to determine the age of a fossil?
• The half-life of a radioactive atom is the time it takes
for half of that atom in a sample to decay and turn into
another element.
• Radioactive isotopes are found in igneous and
metamorphic rock, not sedimentary, and cannot be
used to date fossils.
• If you know what the unstable atom is (Carbon 14)
and you know what it turns into as it decays
(Nitrogen 14).
• And you know the rate at which the unstable atom
decays/turns into something else
It takes 5,730 years for ½ of Carbon 14 to
turn into Nitrogen 14
• You can measure the amount of the unstable atom
in the rock….and compare that to the amount of the
new atom
• This will tell you the age of the sample rock.
Most radioactive isotopes have rapid rates of
decay (that is, short half-lives) and lose their
radioactivity within a few days or years.
Some isotopes, however, decay slowly, and several of these
are used as geologic clocks. The parent isotopes and
corresponding daughter products most commonly used to
determine the ages of ancient rocks are listed below:
Parent Isotope
Stable Daughter
Product
Currently Accepted
Half-Life Values
Uranium-238
Lead-206
4.5 billion years
Uranium-235
Lead-207
704 million years
Thorium-232
Lead-208
14.0 billion years
Rubidium-87
Strontium-87
48.8 billion years
Potassium-40
Argon-40
1.25 billion years
Samarium-147
Neodymium-143
106 billion years
What is stasis?
• Stasis is the term used to describe a
period of time during which organisms
don’t seem to change their forms during a
lengthy presence in the fossil record.
What Fossils can show us
• Gradualism- evolution at a slow and more
steady rate
OR…..
• Punctuated Equilibrium- stable environments followed
by rapid change periods. (predation pressure, food
supply and climate
What can an incomplete fossil
record indicate?
• The sudden disappearance of many life
forms in the fossil record suggests that
a mass extinction occurred. For those
species that survived a mass extinction,
new ecological niches became available.
This may have led to rapid evolution,
which would appear to be a “sudden
appearance” in the fossil record of many
different species, also known as adaptive
radiation
What is adaptive radiation?
• Adaptive radiation - the evolutionary
division of a group of organisms into
diverse groups over a short period of
geologic time