Absolute Age

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Absolute Age

• The actual age of a fossil or rock formation

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What are atoms?
The smallest unit of matter that makes up
everything on Earth.
What are elements?
Matter that is made up of the same atoms.
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What is a radioactive element?

• The atoms of many elements exist in different
  forms.
• Most of these forms are stable and do not change.
  
• But some of these forms are said to be unstable
  elements.
• Its these unstable elements that are called
  radioactive.

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What are some examples of radioactive elements?

• Carbon -12 (stable) Carbon-14 (unstable)
• Potassium 39 (stable) Potassium-40 (unstable)

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What is radioactive decay?

• Radioactive (unstable) elements want to be
  stable.
• The atoms of an unstable element (parent
  material) break down to become atoms of another
  element (daughter material).
• This process of an unstable element breaking down
  to become a stable element is called RADIOACTIVE
  DECAY

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What is radioactive dating?

• Radioactive dating is how scientists use
  radioactive elements to determine the absolute
  age of fossils rocks.

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Why are radioactive elements used to determine
the absolute age of rocks fossils?

• The radioactive decay of unstable elements,
  always happens at the same rate (speed).
• If you know how fast it breaks down, then you can
  figure out how much time has passed by.

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What is a half-life?

• The time it takes for a radioactive element to
  decay (become stable) is measured in half-lives.
• A half Life is the amount of time it takes for
  half of the radioactive atoms (unstable atoms) in
  a sample to change into a stable element.
• Different radioactive elements have different
  half-lives.

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What are some examples of radioactive elements
half-lives?

• Carbon-14 changes into Nitrogen-14
• half-life of 5,730 yrs
• Potassium-40 changes into Argon-40
• Half-life of 1.3 billion yrs
• Urianium-235 eventually changes into Lead-207
• Half-life of 704 million yrs
• Urianium-238 eventually changes into Lead-206
• Half-life of 4.5 billion yrs

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Half-life Example

• The half-life of C-14 is about 5700 years.
• (Every 5700 years, HALF of the C-14 changes!)
• You have 60 grams of Carbon-14.
• After 5700 years pass, how much C-14 would you
  have? N-14?
• Now you have 30g of C-14 30g of N-14
• Another 5700 years go by.
• How much C-14 would you have? N-14?
• 15g of C-14 45g of N-14
• This would continue until all the unstable
  element becomes stable.

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How is absolute age found from radioactive dating?

• In radioactive dating, scientists first find out
  how much radioactive element is in the sample.
• Then, they compare the radioactive amount to the
  stable amount.
• The ratio between stable and unstable lets
  scientists know how many half-lives the fossil or
  rock has gone through, and therefore, how old
  they are.

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Radioactive dating can only be used on what?

• Absolute age can only be determined for igneous
  rocks
• Any fossils that have some organic parts
  remaining
• for example original remains, carbon film, bones
  that are only partially petrified.

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When does radioactive decay begin?

• In non-living things, radioactive decay starts as
  soon as the magma or lava hardens.
• OR
• In living things, every time an organism dies a
  stopwatch starts ticking.
• Death starts the stopwatch.
• Science can read it.

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Why cant we find the absolute age of sedimentary
rocks or of fossils made from sediments?

• Sedimentary rocks and fossils made from sediments
  are formed from millions of pieces of particles
  that come from rocks of all different ages.
• Radioactive dating would find the ages of the
  particles not the age of the whole rock.
• Wed never know how old the rock really is!

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How do scientists date sedimentary rocks?

• To date sedimentary rocks, scientists find the
  age of any intrusions or extrusions that are near
  the sedimentary rock.
• So, any layer of sedimentary rock above an
  intrusion or extrusion, is YOUNGER! Any
  sedimentary layer found below an extrusion is
  older.
• (RELATIVE AGE!!!)

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How old is the Earth?

• The oldest rocks ever found on the Earth have
  been dated at about 4.0 billion years old, but
  scientists believe the Earth is really
• 4.6 billion years old.

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How do we know how old the Earth is?

• Scientist believe the Earth and the moon formed
  at the same time.
• Scientist have dated moon rock brought back to
  Earth by astronauts.
• Therefore the Earth is believed to be at least as
  old as the moon rocks.