DO NOW

What is stratigraphy? Write a statement about the age of the various layers (and fossils that may be found in those layers) you observe in the strata model below.

Paleontology

What similarities are exhibited by these horses? What differences?

Fossils, defined

• The remains or impression of a prehistoric organism preserved in petrified form or as a mold or cast in rock.

Paleontology Essays Debrief

• Fossils can be formed in many ways:– Mineral replacement– Cooled ash/lava encasing

an organism– Arctic Ice (mammoth)– Tree Sap (insects)– Footprints (“trace fossils”)

• Bones are a typically fossilized tissue.

• The theory of Pangea/plate tectonics suggests that changes in land connections allowed some living organisms to move to new areas.

• This changed the “environment” in which certain things lived.

How do you think the movement of plates affected GROUPS of organisms

living in Earth’s past?

There are a few ways to determine age of fossils:– Indirectly, based on where it was found (“relative”

dating)… “younger vs. older”– Directly, based on the fossil itself (“absolute”

dating) using elements that make up the fossil• Go chemistry!• Radiometric Dating types:

1. Radiocarbon Dating (fairly young organic material; uses Carbon-14)

2. Potassium-Argon Dating (rocks)

3. Uranium-Lead Dating (realllly old rocks)

Dating Fossils

• Radioactive Isotope: Elements that undergo steady decay and can be useful for determining the age of objects.– Examples: C-14

• Half-Life is a measurement of time involving radioactive isotope decay

• One half-life is the amount of time it takes for half of the atoms in an object to change into something else (which varies for each element/substance). This change is considered to be the “decay”.

• Scientists can apply the concept of half life and calculate approximate age by looking at how much “stuff” is left in the object (usually a fossil, rock, or something they are interested in dating… haha. Get it?).

Let’s model decay!

Fossil = a rock of M&Ms

What do you understand from this diagram? How does half life apply?

So, if you have a fossil (or rock surrounding it), how can you

know how old it is?

Title a new page: Carbon 14 Dating

No problemo!The half life of iron-59 is 45.1 days. If you start with a

36g sample, how long will it take until you only have 1.13g left? How many half-lives did that process take?

No. of Half Lives Time Amount of Sample Left

Try this…

The half life of Iodine-131 is 8.1 days. How much of a 20g sample will be left after 32.4 days? What does 131 refer to?

Isotopes Commonly Usedfor Radiometric Dating

IsotopesHalf-life(years)

Effective Dating Range(years)

Dating Sample Key Fission Product

Lutetium-176 Hafnium-176 37.8 billion early Earth

Uranium-238 Lead-206 4.468 billion 10 million to origin of Earth

Uranium-235 Lead-207 704 million 10 million to origin of Earth

Rubidium-87 Strontium-87 48.8 billion 10 million to origin of Earth

Potassium-40 Argon-40 1.277 billion 100,000 to origin of Earth

Carbon-14 Nitrogen-14 5730 ± 40 0-100,000

Note: the half-life durations listed in the text sections of this tutorial are rounded off foruranium-238 and potassium-40.

Your Tasks

• Continue The Half Life of M&Ms Lab

• Begin practice set “Radioactive Isotopes, Atoms, Radioactive Dating and Half Life”– Complete at least 5 of the practice problems

• Due Monday (yes, both!)