READ: Important Vocabulary Terms

These are the most important vocabulary terms to learn this week. Please make sure you understand these terms. 

• The principle of uniformitarianism is the idea that the present is the key to the past. If we can understand a geological process now and we find evidence of that same process in the past, then we can assume that the process operated the same way in the past.
  
• Stratigraphy: the study of rock layers. 
  
• Relative age means age in comparison with other rocks, either younger or older. 
  
• Law of Superposition: New rock layers are always deposited on top of existing rock layers. Therefore, deeper layers must be older than layers closer to the surface. 
  
• Law of Lateral Continuity: Rock layers extend laterally, or out to the sides. They may cover very broad areas, especially if they formed at the bottom of ancient seas. Erosion may have worn away some of the rock, but layers on either side of eroded areas will still “match up.”
  
• Law of Original Horizontality: Sediments were deposited in ancient seas in horizontal, or flat, layers. If sedimentary rock layers are tilted, they must have moved after they were deposited.
  
• Law of Cross-Cutting Relationships: Rock layers may have another rock cutting across them. The cut rock layers are older than the rock that cuts across them.
  
• Unconformities: a gap in the sequence of rock layers.