Download Sea-floor Spreading Section 4-4

Sea-floor Spreading
• Mid-ocean ridge- Undersea mountain
chain where new ocean floor is
produced.
Alfred
Harry
Wegener
Hess
• Harry Hess- came up with the theory
of sea-floor spreading.
• Sea-floor spreading- at the mid-ocean
ridge, magma rises from the mantle and
erupts. The magma spreads out,
pushing older rock to both sides of the
ridge.
Picture of Sea-Floor
Spreading
Evidence for sea-floor
spreading:
• 1. Molten material- presence of rocks
that can only form when molten material
hardens quickly after erupting under
water. (Pillow Lava)
• 2. Evidence from magnetic stripes in
the rock of the ocean floor.
• 3. Drilling Samples- Glomar
Challenger (drilling ship) brought up
rock samples from the ocean floor and
found that the farther away from the
ridge the samples were taken, the older
the rocks were. Youngest rocks were in
the center of the ridges.
Subduction at Deep-Ocean
Trenches:
• Deep-ocean trench- deep underwater
canyons where old ocean floor
eventually sinks.
• Subduction- process by which the
ocean floor sinks beneath a trench and
back into the mantle.