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large breaks in the sedimentary rock record that can be used to measure long periods of geologic time.
a stone tool that has been worked only on one side (face).
a principal in geology that states that all natural laws are constant, that the present processes of today are the same as those acted in the past, that geologic change is slow and of a uniform rate, and that the earth is fundamentally the same today as it was at the time of its formation; proposed by Charles Lyell (1797-1875).
Upper Paleolithic

[syn. New Stone Age or Neolithic] the time period of tool approximately dated between 40,000 years ago to the present; tools associated with this time period deal with plant domestication and agriculture, and more diverse in their manufacture and utility than seen in previous eras.