Transcript DO NOW Monday 9/20

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?
Dating Fossils
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)
• 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 Used
for Radiometric Dating
Isotopes
Half-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 for
uranium-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!)