SEAFLOOR SEAFLOOR SPREADINGSPREADING

Atlantic Getting Bigger

B40b

SEAFLOOR SEAFLOOR SPREADINGSPREADING

• Idea that the ocean bottom is getting larger.

• Atlantic Ocean

• Proposed by Harry Hess

• Evidence in rocks on ocean floor.

MID-ATLANTIC RIDGEMID-ATLANTIC RIDGE• mid-ocean ridge

• found running down center of Atlantic Ocean

• series of mountains on either side

ROCK AGESROCK AGES• 1 - youngest rocks nearest the ridge

• oldest rocks next to continents

• identical pattern on both sides

• THEREFORE: new rocks are forming

(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)

MAGNETIC REVERSAL MAGNETIC REVERSAL INDICATORSINDICATORS

• rocks on ocean bottom reflect earth’s magnetic reversals

• THEREFORE: new rocks are forming

(B3, Figure 10)

ASSIGNMENTASSIGNMENT• 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.