1. Do now:
Read 4.2

2. You will learn to explain seafloor spreading.
Module F: 4.2
Seafloor Spreading
Objectives:
You will learn to explain seafloor spreading.
You will learn to recognize how age and magnetic clues support the theory of seafloor spreading.

3. Clues on the Ocean Floor
- invention of ____________________ allowed the construction of accurate maps of the ______ floor
- using sound waves, researchers discovered an ___________ system of _______, or __________, and valleys like those found on the ____________
echo-sounding devices
ocean
underwater
ridges
mountains
continents

4. Seafloor Spreading!!! Harry Hess
- Early 1960s: __________ proposed this theory
- the idea that _______ from Earth’s _______ rises to the surface at mid-ocean ridges and cools to form new ________, which new magma slowly pushes away from the ridge
magma
mantle
seafloor

5. Evidence for Seafloor Spreading!!!
1. Age Evidence
__________________
____________
2. Magnetic Clues

6. 1. Age Evidence
- there were no rocks older than
___________ years, however, some ___________ rocks are almost
_________ years old
- youngest rocks were at
_________________
- age of rocks became ______ farther from the ridges on both sides
180 million
continental
4 billion
mid-ocean ridges
older

7. 2. Magnetic Clues - magnetic data is recorded by a ______________
- rocks on the ______ floor showed magnetic reversals
- the magnetic alignment of the rocks reverses back and forth in strips ________ to the mid-ocean ______
magnetometer
ocean
parallel
ridge

9. LET’S REVIEW!
The invention of _____________ allowed the construction of accurate maps of the ocean floor.
What are mid-ocean ridges?
Who discovered the idea of seafloor spreading?
What is a trench? When is one formed?
What two pieces of evidence proved the theory of seafloor spreading to be correct?

10. Homework!!! Read section 4.2 and do questions #1-5 Due Wednesday
Notes Packet due Thursday
Study for 4.2 quiz Thursday