Do now: Read 4.2

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.

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

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

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

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

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

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?

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