8.1 Science

• How do fossils form?

  • Fossils are the remains or evidence of once-living organisms.

  • Help us understand how organisms have changed over time.

  • Most soft parts are broken down quickly, and only hard parts (bones, shells, teeth) fossilize.

  • Some fossils form from impressions that are filled in & hardened.

    Fossil types:

• Mineralization: Minerals fill in small spaces and replace tissues.

• Carbonization: Pressure drives out the organism's liquid & gases; the carbon outline remains.

• Molds & casts: Sediments encase hard parts.

• Trace evidence of an organism.

• Original material: Cells are buried in a deoxygenated environment where bacteria can't break them down (trapped in amber).

What can a fossil tell us about time?

• The fossil record contains all the fossils and shows change over time.

• Relative-age dating: Use the layers of rock to determine if one fossil is older than another.

• Absolute-age dating: Carbon decays at a specific rate, so we can put a number to a fossil that has been carbonized.

• Relative and absolute ages create the geologic time scale: a chart that divides Earth's history into different time units

• Eons- 4 hundreds of millions years

• Eras (hundreds of millions of years) are the largest divisions.

• Epochs (short term) are the smallest, reflecting changes in climate, geology, or life.

• Scientists have found 5 times in the fossil record where fossils in the lower layers no longer appear in layers above: mass extinction events.

• Environmental changes cause extinction events.

• Sudden changes: tectonic plate movement, sea level changes, mountain forming.

  How do fossils change over time?

• Fossils show common ancestors of modern organisms that shared similar body plans & structures.