relative dating

• Method 1 is evolutionary change in fossils. As geological time has progressed organisms evolve and become more complex. 
• Stratigraphic methods are relative data using rock layers themselves. 
• Method 2 is original horizontality. Most rocks were deposited horizontally. If layers are no longer horizontal it suggests something has moved them after they were deposited. 
• Method 3 is lateral continuity. Layers of sediment initially extend laterally in all directions. Rocks that are separated by a valley or other feature must have been continuous.   
• Method 4 is the principle of superposition. The rocks at the bottom are always the oldest. 
• Method 5 is included fragments. Fragments from older rock can be found within younger rock. For example: xenoliths and pebbles in conglomerate.  
• Method 6 is cross cutting relationships. Features that cut through rocks are younger than the rocks they cut through. Faults are younger than they displace. Unconformities are formed due to erosion after beds were deposited. The unconformity cuts across older beds. Folds are formed after the rocks have been layered down due to compression. Faults are formed after rocks have been subject to tension, compression or shear forces.