Chapter 10.1 Harry Hess

Question 1

Harry Hess: Seafloor Spreading

Answer 1

The theory of seafloor spreading:
- Magma from active volcanoes at the underwater mountain ridges was forming a “new” crust and pushing the seafloor outwards.
- This theory provided the mechanism for how continental drift occurs.

Question 2

Evidence: Age of the seafloor

Answer 2

Rocks near the ridges were relatively young, while rock near the trenches were relatively old.

Question 3

Evidence: Sediment Thickness

Answer 3

The layer of sediment near ridges were thinner (young rock = less time for sediments to accumulate)
The layer of sediment near trenches were thicker. (older rock = more time)

Question 4

Evidence: Magnetic Striping

Answer 4

• Earth’s magnetic North and South flip around every 300,000 years.
• Molten rock that rises at ridges will align in the direction of the Earth’s magnetic field at that time.