Evidence for Evolution I: The Geological Record

How old is the Earth? Creationism: – years Science: 4.54 billion years

How do we know? Creationism: – 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 ~ 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