The Fossil Record

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The Fossil Record

• The estimated age of the Earth is about 4.5
  billion years (thats 31.5 billion in dog years).
  
• About 1 billion years after thatsome life stuff
  started happening (prokaryotesin case yer
  interested).
• So, for about 3-4 billion years, life has been
  evolving.
• 3 BYA the party startsCyanobacteria (forms
  stromatolite fossilsremember that for high
  school bio)
• 2.7 BYA Eukaryotes show upthey bring snacks.

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• 2.2 BYA we get some atmospheric O2. This is the
  result of photosynthesis (from the
  cyanobacteriaaka blue-green algae).
• From about 2.5-1.2 BYA its pretty quiet.
• About 1.2 BYA we get us some metazoansmulticellul
  ar organisms.
• The longest period of time in the geologic time
  table is called the Precambrian Time (technically
  its a supereon).
• Okso how do we figure this all out?

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The Endosymbiont Theory

• Theres a really cool theory which postulates
  that mitochondria and chloroplasts were organisms
  that were food for other larger organisms.
• Eventually these organisms became interdependent
  and could not live without each othera symbiotic
  relationship.
• Living inside the larger organisms, the
  chloroplasts produced food and oxygen, and the
  mitochondria used food and oxygen to produce ATP.
  

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One Way To Visualize This Stuff
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Dating Fossils Rocks

• Fossils are the petrified remains of once-living
  organisms. There are a few kinds
• Mineralization the bone or tissue is replaced by
  minerals (there are several types).
• Molds and Casts
• Trace fossils tracks and burrows.

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How Old?

• There are two types of datingrelative and
  absolute.
• Relative Dating Sediment builds up over timeif
  the layers are undisturbed, the older stuff is on
  the bottom (this is called Superposition).
• You cant get an actual time in years this way,
  but you can say fossil A is older or younger than
  fossil B.

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• Absolute Dating Radioactive isotopes are used to
  figure out an actual age in years.
• Isotopes are elements that are radioactive and
  unstable. They decay at a measurable rate. When
  this happens, they breakdown into another
  element.
• By measuring the ratio of isotope to breakdown
  product, we calculate the age of the rock.
• The time it takes for half of an isotope sample
  to break down is calledhalf-life.

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Some Isotopes Used for Absolute Dating

• Parent-------Daughter
• Carbon-14gtNitrogen half-life 5,730 years
• Potassium-40gtArgon-40 HL 1.3 bill. Yrs.
• Uranium-235gtLead-207 HL 700 mill. Yrs
• That means for example that if you had 100 grams
  of U-235, after 700 million years had passed
  youd have 50 grams left (along with 50 grams of
  Lead-207)
• That also meansyou cant use C-14 to calculate
  the age of dinosaurs fossils. Why? Cuzit
  breaks down too quickly! You can use other
  isotopes though?

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As the amount of Parent Decreases the amount of
Daughter Increases!
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Try This

• Carbon-14 has a half-life of 5,730 years.
• If you had a 10 gram sample of C-14, how many
  years would take for there to be 2.5 grams left?
• If you had a 20 gram sample of C-14, how much
  would remain after 22,920 years?