Transcript Evidence for Evolution I: The Geological Record

Homework Questions
PG 287
Q. 1: The chances of one individual being born with
a beneficial mutation is very low. How then is it
possible for mutations to play such a key role in
evolution?
ANSWER:
Evolution acts on such large time scales that even
though the chance of a beneficial mutation is
rare, there is enough time for many to occur and
proliferate.
Homework Questions
• PG. 287
Q3: Explain why harmful mutations do not
accumulate over time and cause harm to
populations.
ANSWER:
Harmful mutations cause harm to the individual
and evolution will select against individuals with
harmful mutations. These individuals will not
breed with others, causing the harmful mutation
to disappear from the population.
Homework Questions
• PG. 287
Q9: How do the genetic diversity of a population and
mutation rates limit the ability of breeders to create
organisms with desired traits?
ANSWER:
Hint: Think of the blue rose.
Breeders can only work with the genetic diversity that is
already present in the organisms population. If a trait does
not exist in an organisms genome, a breeder cannot just
create that mutation. Mutations are random and rare. This
means that beneficial mutations are unlikely to happen.
Homework Questions
• PG. 319
Q28: What is artifical selection, and why is it called
artificial?
ANSWER:
Artificial selection is directed breeding in which
individuals that exhibit a particular trait are
chosen as parents of the next generation. It’s
called artificial because it is controlled by human
choice, not by nature.
Evidence for Evolution I: The
Geological Record
How old is the Earth?
Creationism:
5 000 – 10 000 years
Science:
4.54 billion years
How do we know?
Creationism:
5 000 – 10 000 years
- various religious texts
Science:
4.54 billion years
- geology, paleontology
Scientific Methods for Dating
the Earth: Absolute Dating
Absolute Dating - determining a specific
age of an object or event
Absolute Dating: Radiometric Dating
• Radioisotope - an atom with an unstable
nucleus capable of undergoing decay
• Radioactive atoms give off particles over time
and change into another isotope
Example: Carbon-14
decays to Nitrogen-14
Radiometric Dating
• This decay occurs in a
predictable way
• The amount of time it
takes for 50% of these
isotopes to decay is
called its Half-Life
• After one half-life, 1/2
the C-14 isotopes remain
• After two half-lifes, ¼
(half of ½) remains
Radiometric Dating
• After two half-lifes, ¼
(half of ½) remains
• After three half-lifes,
how much C-14
remains?
– 1/8 remains (half of
¼)
Half-Life
• Carbon-14 is often used to age younger fossils:
it has a half-life of 5730 years (can age fossils
as old as ~60 000 years)
• Organisms take in C-14 throughout their life
and when they die they cannot take in
anymore
• Then the total amount of C-14 begins to decay
predictably
Carbon-14 undergoes decay
to form Nitrogen-14. By
comparing the amount of
Carbon-14 to Nitrogen-14, we
can determine the age of a
fossil using the half-life.
Half-Life
• Carbon-14 has a half-life of 5730 years
• Therefore after 5730 years, an object will have ½
the C-14 isotopes it once did
– How many years would it take for an object to have ¼
the C-14 isotopes it once did?
– What about 1/8?
C-14 Half-Life
After two half
lives, ¼ remains
After three halflives, 1/8 remains
Radiometric Evidence
• Other examples of radiometric
dating:
– potassium-argon: 700 million
year half life
– uranium-lead: 1.3 billion year
half life
• The oldest rock on Earth is dated
to 4.4 billion years
• Some solar system meteorites
have been dated to 4.5 billion
years
Labradorite
• Rock found in Labrador,
Newfoundland
• Incredibly old!
• 1.29 – 1.35 billion years
old!
Is Age Significant?
• Of course it is!
• Evolution is a process
that occurs over
hundreds of thousands
or millions of years
• Radiometric dating
suggests our planet is
not just millions, but
billions of years old
Scientific Methods for Dating
the Earth: Relative Dating
Relative Dating – the science of
determining events relative to each other
Relative Dating
• The method that was used before we could
use radioisotopes to date materials
• Some materials don’t have radioactive
isotopes so we must use relative dating
• Still useful today especially when used with
absolute dating
Relative
Dating
Absolute
Dating
Evidence for Evolution: The
Fossil Record
Fossil – ancient remains, impressions, or
traces of an organism that have been
preserved in rocks or other mineral
deposits
Fossil Formation
• Fossils only form in specific conditions
• Oxygen must be absent, to prevent the body from
being decomposed by microorganisms
• Hard shells and bones are more likely to be
preserved than soft-bodies organisms
• Organisms may be preserved whole in amber
Theory of Plate Tectonics
• The scientific theory
that describes largescale movements
and features of
Earth’s crust
• The Earth’s crust is
made of plates
• These plates move
around
• Move very slowly
Fossils and Plate Tectonics
• Fossils of the same
species have been
found in Africa, India,
and Antarctica, but
nowhere else on earth
• Plate tectonic theory
explains this
– How?
Pangaea
Fossils and Plate Tectonics
• Plate tectonic theory
explains this
– How?
• Species would have
lived together where all
three continents
connected at some
point in history
Fossils: Significance to
Evolution?
• Fossils give us a snapshot of early species
• They help us understand where new variations
have arisen
• They suggest transitions between species
The Fossil Record
- Fossilized species
often resemble
modern species
The Fossil Record
• Despite similarities to modern species, most
fossilized species are extinct today
• Example:
– Carcharodon megalodon  Great White shark
The Megalodon
The Fossil Record
• Sometimes, if we are lucky, fossil lineages can
be very detailed
• We can see many steps in the evolution of a
species
Example:
Whale
Evolution
Questions
• Textbook
• Page 313 #2, 3a
• Page 320 # 31, 32, 33abc