PRINCIPLES OF RELATIVE DATING

• uniformitarianism 


  the present is the key to the past, which is based on the principal that natural laws have remained the same throughout time
• "the key of understanding the past, is understanding the present"
• different types of rocks provide hints about earth's past

  • igneous
  • metamorphic
  • sedimentary
• igneous


  records of volcanic activities, specific age of a material
• metamorphic 


  movement of plates, how continues drifted away from one another
• sedimentary


  climate records, previous environmental conditions, holds fossil
• most of the rocks exposed at the surface of earth are SEDIMENTARY
• sedimentary


  formed from particles of older rocks that have been broken apart by water or wind
• law of superposition


  • sedimentary rocks are formed particle by particle and bed by bed
  • layers are piled one top of the other
  • bed must be older than any bed top of it
  • rock layers at the bottom are older than those on top of them
• law of lateral continuity


  • laterally continous and may be broken up or displaced by later events
  • this can happpen when a river or stream erodes a portion of the the rock layers
  • faulting occur
  • any rock layer that is separated by a valley or any feature caused by erosion are originally continous
• law of original horizontality


  • rock layers formed in a horizontal position
  • any disturbance such as folding and faulting must have have been happened after the formation of the deviated rock layers
• law of cross-cutting 


  • any rock or fault that cuts across other rocks is younger than those cuts across
• principle of inclusion


  • any inclusion such as fossils or other rock materials found in a rock layers are older than the rock that contains it
• principle of unconformity 


  • surface that reflects a time of nondeposition or erosion
  • presence of unconformity in rock layers means that there is missing record of time
  • break in time
• law faunal succession 


  • fossils found in a rock layer occur in a definite sequence and in predictable manner even though they are found in different locations