Download Seafloor Spreading

Seafloor Spreading
Chapter 10, Section 2
Mapping the Ocean Floor
• Pre-WWI
– Ropes were lowered from boats to measure
depth.
• 1940’s/1950’s
– Developed use of sound waves to map depth
of the ocean floor.
• Found that the ocean floor actually had a series of
ridges and valleys (mid-ocean ridges).
Seafloor Spreading
• Developed by Harry Hess in the 1960’s.
• Proposed that:
– Hot, less dense material beneath the ocean floor rises
toward the surface at mid ocean ridges
– As the material approaches the surface it moves
sideways, pulling the ocean floor apart at the center
of the mid ocean ridge
– Magma erupts from the resulting cracks and cools to
form new ocean crust
– Through time the new ocean crust moves away from
the center of the mid-ocean ridge becoming cooler
(and thus more dense) and sinks
Support for Seafloor Spreading
• 1968 – Glomar Challenger
– Research vessel that drilled into the ocean
floor to obtain rock samples.
– Discovered that the youngest ocean crust was
closest to the center of the mid-ocean ridge.
Support for Seafloor Spreading
• Magnetic Reversals
– At the time that rocks with iron-bearing
minerals form, the direction of Earth’s
magnetic field is recorded in the orientation of
the minerals.
– Scientists have found that many reversals
have occurred in the magnetic field and are
recorded in strips of the ocean floor that run
parallel to each other.