GEL Week 2- Sea floor spreading (2)

How is continental drift shown?

Tech improvements in the 1950s led to the creation of sonar, and showed deep parts of the ocean floor.

What did sonar mapping reveal?

Sonar mapping of the ocean floor revealed:

trenches

mid-ocean ridges

seamounts and guyots

Trenches

near land, deep structures in the ocean

Mid ocean ridges (MOR)

A mountain range found in every ocean

Seamounts and Guyots

volcanic islands or former islands existing near the ocean floor

Oceanic crust

Oceanic crust is covered by sediment. It is thick near the continents, and thin (or absent) at the MOR.

What are some additional characteristics of oceanic crust?

Oceanic crust is basaltic. There is high heat flow at the MOR

Who was Harry Hess and why was he significant?

Harry Hess was a princeton geologist and coined the term “sea-floor spreading” in 1962

Sea floor spreading

The spreading of the sea floor contributing to the continents moving away from each other

What is the process of seafloor spreading?

1- New crust erupts at the MOR (new basalt, no sediment)

2- material comes behind it, moves away from ridges in either direction (gathers sediment)

3- At trenches, the sea floor dives back into the mantle

How was Hess’ theory proved? How can we prove the rocks were moving?

Paleomagnetism

What is paleomagnetism?

Studying alignment of magnetic minerals with respect to the magnetic field of the Earth

How does paleomagnetism work?

As molten materials cool, magnetic materials align with the magnetic field.

How can we study paleomagnetism and why?

Study layered lava flows, see what the magnetic field was like in different layers to disocver what the magnetism was like at the time using radioactive decay

What did studies from lava flows reveal?

Studies revealed reversals in polarity. North and south poles switch, a magnetic reversal

How are reversals recorded?

Reversals are recorded globally in lava flows

Where do magnetic reversals occur?

Magnetic reversals show up in oceanic crust

Proof of sea floor spreading

Polarity reversals are symmetric across the MOR

Age increases away from the MOR on both sides