B40b SEAFLOOR SPREADING Atlantic Getting Bigger
SEAFLOOR SPREADING • Idea that the ocean bottom is getting larger. • Atlantic Ocean • Proposed by Harry Hess • Evidence in rocks on ocean floor.
mid-ocean ridge found running down center of Atlantic Ocean series of mountains on either side MID-ATLANTIC RIDGE
1 - youngest rocks nearest the ridge oldest rocks next to continents identical pattern on both sides THEREFORE: new rocks are forming ROCK AGES (B3, Figure 9)
2 - oldest rocks on ocean floor = 200 million years old oldest rocks on continents = 4.6 billion years old THEREFORE: new rocks are forming (B3, Figure 9)
rocks on ocean bottom reflect earth’s magnetic reversals THEREFORE: new rocks are forming MAGNETIC REVERSAL INDICATORS (B3, Figure 10)
ASSIGNMENT • Draw a section of the ocean floor and mantle flanking the mid-Atlantic ridge. • Use different colors to represent different rock ages. • Label: mid-Atlantic ridge and direction of plate movement.