I can: describe what happens during Sea Floor Spreading DO NOW: What is a Mid- ocean Ridge?

Vocabulary Sonar Sea-floor spreading Deep-ocean trench Subduction Mid-ocean ridge

60 years ago, in the 1950’s, Sonar was invented.

Sea-Floor Spreading Sonar - a device that bounces sound waves off under-water objects and then records the echoes of these sound waves. The time it takes for the echo to arrive indicates the distance to the object.

Bats use it!

So do dolphins So do dolphins!

Sonar brought Wegner’s theory back to life!

Mid-Ocean Ridge

Mid-Ocean Ridge – the longest chain of mountains in the world---these are divergent plate boundaries (seafloor moves apart.

Harry Hess : American Geologist

Harry Hess No! Harry Hess, not Harry Potter!

Sea-Floor Spreading Harry Hess 1960

An American geologist who studied mid-ocean ridges. He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.

Sea floor spreads as if there are 2 conveyor belts on either side

I can: Explain the evidence for sea floor spreading DO NOW: 1.What is subduction? 2.What is a deep-ocean trench?

Subduction is a process where the ocean floor sinks back into the mantle at a deep ocean trench.

Sea floor spreads as if there are 2 conveyor belts on either side

VERY ACTIVE

Pillow Rock forms when magma cools in water. This is evidence of volcanic activity!

Think-Pair-Share: How can we know for sure that the sea floor is actually spreading?

Sea Floor Spreading Evidence 1.Age of rocks at the mid-ocean ridge 2.Magnetic clues in rocks

Evidence 1: Age of Rocks Scientists have collected rock samples at the mid- ocean ridge Youngest rocks located at the ridges. Rocks are increasingly older as you move farther from the ridge Older rocks Older rocks Magma

How is this Possible? Propose a mechanism (the way in which this happens) Older rocks Older rocks Magma Evidence 1: Age of Rocks

I can: Explain the evidence for sea floor spreading DO NOW: 1.What information from rocks at the mid-ocean ridge gives evidence for sea-floor spreading? 2.How is this possible? Describe the mechanism.

1.Magma rises up to the ridge 2.Rock layers near the ridge are pushed away 3.Molten rock cools down creating new sea floor Older rocks Older rocks Magma Sea Floor Spreading: Mechanism

DO NOW: 1.What information from rocks at the mid-ocean ridge gives evidence for sea-floor spreading? 2.How is this possible? Describe the mechanism. This shows you the age of the sea floor. The red areas are new rocks and the blue areas are the oldest oceanic rock.

Evidence 2: Magnetic Clues A magnet has a north end and a south end with a magnetic field—Invisible lines of magnetic force

-The Earth is a giant magnet -Compass needle points to the north pole (following the magnetic field) -Magnetic field protects Earth from solar wind (high energy particles form the sun) Evidence 2: Magnetic Clues

Magnetosphere -magnetic field that protects the earth Solar wind -high energy particles from the sun that flow into the space

-Earths magnetic force field can reverse (Magnetic reversal) -Happens every thousand years North South Normal magnetic polarity South to north Reversed magnetic polarity North to South Evidence 2: Magnetic Clues

-Molten rock contains magnetic minerals and iron that line up with Earth’s magnetic field -Earth’s magnetic field is recorded in the rock when it cools down Evidence 2: Magnetic Clues

What would the magnetic field recorded in these rocks look like if the sea-floor is spreading? -We know that the Earth’s magnetic field reverses every thousand years -This magnetic field is recorded in the rocks as they move and the sea-floor spreads Draw a diagram of the sea floor to show this. Evidence 2: Magnetic Clues

What would the magnetic field recorded in these rocks look like if the sea-floor is spreading?

Normal magnetic polarity Reversed magnetic polarity

Evidence 2: Magnetic Clues

Iceland is spreading open on the Mid- Atlantic Ridge!

Can you see where the Mid-Atlantic Ridge bisects Iceland? This is a rift valley!

Sea Floor Spreading Evidence Age of rocks at the mid-ocean ridge Magnetic stripes

If new crust is being added to Earth’s surface, is Earth getting bigger?

Subduction is a process where the ocean floor sinks back into the mantle at a deep ocean trench.