Evidence for Evolution I: The Geological Record. How old is the Earth? Creationism: 5 000 – 10 000...
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Transcript of Evidence for Evolution I: The Geological Record. How old is the Earth? Creationism: 5 000 – 10 000...
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 half-lives, 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 large-scale 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
How old are my fossils?
• How would you date my fossils?
• These fossils are from the Ordovician and Silurian Period
• Between 250 – 540 million years old!
Questions• Textbook• Page 313 #2, 3a• Page 320 # 31, 32, 33abc