Fossils

1
Fossils

• Fossils are found in Sedimentary rocks
• They help provide information of life forms that
  lived thousands of years ago.

2
Types of Fossils

• Petrified Minerals have filled in where an
  organisms once was
• Molds A hollow area that an organism has left.
  
• Cast A copy of the shape of the organism
  (opposite of a mold)
• Carbon Film a thin coating of carbon that is
  left behind when gases have been release by the
  decaying fossil (like a leaf print on a rock)
• Trace An imprint that an organism left behind
  (like a footprint)

3
Bones

• A fossil bone should have different canals and
  webbed structure of the bone.
• You can even try a tongue test. The porous nature
  of some fossil bones will cause it to slightly
  stick to your tongue if you lick it, though you
  might want to have a glass of water handy if you
  feel compelled to try this. 

4
Petrified Fossils

• Fossils in which minerals replace all or part of
  an organism.
• How does this happen?
• Water rich in dissolved minerals seeped into
  spaces, evaporated, leaving the hardened minerals
  behind.
• Example petrified wood

5
Molds and casts

• Most common type of fossil.
• Both copy the shape of the organism.
• A mold is a hollow area of sediment in the shape
  of the organism.
• A cast is a copy of the shape of an organism.

6
Carbon Films

• Carbon film is an extremely thin coating of
  carbon
• How does this happen?
• All organisms are made of carbon. When they are
  buried, the materials that make up the organism
  evaporates. These gases escape leaving carbon
  behind.

7
Trace Fossils

• Trace fossils provide evidence of the activities
  of ancient organisms.
• Examples
• A footprint provide clues about the size and
  behavior, the speed, how many legs it walked on,
  lived alone or with others.
• A trail or burrow can give clues about the size
  and shape of the organism, where it lived, and
  how it obtained food.

8
How old is it?

• Relative Age Its age when compared to others (
  I am older than you)
• Absolute age Its actual or real age
• We use radioactive dating to find this
• Unconformity a gap in the the geological record
  (like from erosion)

9
Laws of Geologic History
10
Law of Superposition

• The oldest layer is at the bottom and the
  youngest layer is at the top.

11

• Law of Crosscutting - In a series of horizontal
  sedimentary beds, if there is an inclusion which
  cuts vertically through them, it must be younger
  than the sediment beds.

12
Law of Inclusions - The intruding rock (Rock A)
must have been there first to provide the
fragments in the younger rock (Rock B)