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