Transcript Absolute Age

Absolute Age
Finding a rock’s birthday
Absolute Age?
• Give an example of an absolute age of a
rock layer…
•That rock layer is 200 million years old.
•Remember, absolute age is the exact
age of a rock layer.
Absolute Age
• Think of determining the absolute age of a
rock layer as finding the rock layer’s
birthday.
• Often impossible to do
• Uses Radiometric Dating
Matter?
• What is MATTER?
•Anything that has mass and takes up
space.
Can you think of some things that could
be called matter?
You
Water
Me
Rocks
Books
Cars
Air
Hair
What are atoms?
• All matter is made up of ATOMS.
• Atoms are so small that we cannot see
them.
• Rocks and Rock layers are made of atoms
too since they are types of matter.
What do atoms look like?
• We’re not sure.
• They are too small to see even with
microscopes.
• We think they look something like this:
Particles
Do all atoms look the same?
NO !!!
There are over
110 ways that
atoms can look
Atoms…
• Stable atoms– they don’t change, they
stay the same.
• Unstable or Radioactive atoms– they
turn into stable atoms over time.
How do unstable atoms decay?
•Over time the
atoms give off:
1.Particles
2.Energy
This is called
RADIOACTIVE
DECAY
Radioactive Decay
• This change from a radioactive atom to a
stable atom is called radioactive decay
How fast do elements decay?
• A certain atom will decay at a constant
speed. The speed never changes for that
type of atom.
• HALF-LIFE = the time it takes for half of
the radioactive element in a substance to
decay into its stable element.
Radioactive decay
The make-up of the intrusion or
extrusion changes.
Newintrusion
elementor extrusion’s make-up has
The
As changed
time goesbecause
by, the of this decay. We will
redsoon
element
decays
see
that we can determine the exact
Here’s
the
andtime
becomes
the
blue
it
was
born
by
seeing
how
much
of
Half-Life
element.
each of the elements is left.
Radioactive
element
What can we date?
• IGNEOUS, METAMORPHIC, FOSSILS
ONLY – because they have a true
birthday.
• Once it’s born, the radioactive elements
start to decay and the clock starts.
What can we date?
• Sedimentary rocks cannot be dated
because they are made of sediment (tiny
pieces of rocks with all sorts of different
birthdays). We would find lots of birthdays
of the sediment, and not the rock layer.
Why not Sedimentary Rocks?
Radioactive
Radioactive Dating
Dating would
would say
say
these
rock
particles
are
these
rocksee
particles
are 50
100
Do you
the problem???
million
million years
years old
old
Let’s say this Sedimentary rock
is actually 20 million years old.
Here are the elements used in
radioactive dating
Radioactive Decay of Potassium-40
100
% of element in rock
90
Potassium-40
80
70
60
50
40
30
20
Argon-40
10
0
0
1.3
2.6
3.9
TIme gone by (in billions of years)
5.2
Potassium – Argon Dating
• Potassium to Argon Dating: It takes
potassium (radioactive element) 1.3 billion
years for half of it to turn into argon (stable
element). Useful for dating the oldest rocks
because of the long half-life.
Potassium
Potassium
1.3 billion years
ROCK
(half-life)
ROCK
Argon
Carbon 14 Dating
• Carbon 14 Dating is useful for dating plant
and animal remains that lived from 500 to
50,000 years ago.
• It cannot be used for very old fossils or
rocks.
Carbon 14 Dating
• Carbon 14 to Nitrogen 14 Dating: All
plants and animals contain Carbon 14
(radioactive element). As the organism
grows, more Carbon 14 is added to it.
When the organism dies, the Carbon 14
starts to decay into Nitrogen 14 (stable
element).
• It is used to date fossils, wood, and bone.