fossils

• what are fossils

  remains of organisms from thousands of years ago which are found in rocks
• what do fossils show us

  evidence of how organisms have adapted over time
• what is the difference between newer and older rocks/fossils

  -older rocks contain fossils of simpler organisms(more different to species today)

  -new rocks contain fossils of more similar fossils to organism today
• what are the three ways fossils form in rocks

  -gradual replacement by minerals

  -from cast and impressions

  -from preservation
• what is gradual replacement by mineral 


  -most fossils happen this way

  -things that don’t decay easily like teeth, bones, shells last a long time when buried

  -eventually replaced by minerals forming rock like substance

  -surrounding sediments also turns to rock and fossil stays distinct inside
• what is casts and impressions in fossil formation 


  -sometimes fossils are formed when organisms are buried in soft material like clay

  -clay hardens around organism and leaves cast of itself

  -animals burrow or plant roots can be preserved in casts

  -footprint can also be pressed into soft materials leaving impressions
• what is preservation in fossil formation 


  -happens in places where no decay happens

  -in amber(sap) and tar pits there is no oxygen or moisture so decay doesn’t happen

  -in glaceries it’s to cold for decay

  -this preserves organism until found in sap, tar and ice
• what are the problems of fossil records 


  -record is incomplete

  -fossilisation is a rare process

  -early life forms were made soft bodied so fewer traces

  -fossils destroyed by geological activity