We Need More Evidence!

Purpose: Prove to yourself that Earth’s continents really

are moving apart.

Trust No One.• So far you have heard three pieces of evidence

suggesting that Earth continents are moving.– Animal Fossils– Plant Fossils– Landforms

• BUT is that good enough? What do you think?• Be a SKEPTIC, discuss other explanations for these

so called pieces of evidence.

Some more evidence• One good thing about scientists is

that they don’t give up until they find the truth. (At least the good, honest, and true scientists don’t.)

• SO, let us see what they came up with.

Evidence 1• I am going to show you two videos discussing

scientific evidence that the continents are moving. Please answer the following:

1. Describe in detail what the scientists observed?

2. Where did they observe it? How big was it?

3. What evidence did they find proving that what they observed was the cause of the continents moving apart?

Sea-Floor Spreading

• Other pieces of evidence suggested that the continents of Africa & S. America had been attached.

• However, those pieces of evidence did not explain HOW they MOVED APART.

• Sea-Floor Spreading provides a cause for the movement of the continents.

Sea-Floor Spreading• Mid-Atlantic Ridge

– 1 Mile High– 12,000 Miles Long– Part of larger 50,000 mile world-wide

underwater mountain chain.• Age of rocks get older the further you get

from the ridge AND younger the closer you get to the ridge.

SO…

• If the sea-floor is spreading, does that mean the Earth is getting larger?

• Choose a side, either yes or no.

• Come up with some ideas to support your choice.

Even the Earth Recycles!

• Subduction

–The Process through which the crust plunges back into the Earth.

• Some absorbed by Mantle.

• Some forced upward becoming…

–Volcanoes

–Mountains

Can a Lil’ Crack Do All That?

• Purpose: Can a crack in the sea floor cause entire continents to move or is there more to it?

What do you think?• Based on what you know so far about the

Earth’s Interior, do you think there could be more going on inside the Earth than just Sea-Floor Spreading?

• Spend the next three minutes thinking about what else could be causing the continents to drift?

Could we somehow make a model?

• No, we can’t melt rocks, but can we do something else?

How About A Demonstration?

• I will call you to the front. 10 at a time. While I am calling groups up please read pages 376-380. Take Notes.

Explain What You Observed

• What is heat?

• What does it do to the water?

• How does the water change?

• How does all of this relate to the way the water moves?

• How does this relate to the movement of the Earth’s Crust?

Why Does This Motion Occur?• Convection Currents (Hypothesis)

–The movement of materials due to differences in temperature.

•High Temp=Higher Energy=

Spread Out=Less Dense=Float

•Low Temp=Lower Energy= Condense=More Dense= Sink

The Continents get Carried Away

What Happens When the Plates Move?

• Earthquakes

• Volcanoes• Mountain Building

But Why?

• Please discuss some ideas for why the movement of Earth’s plates leads to:

–Earthquakes

–Volcanoes

–Mountains

How About A Video?• Don’t Forget About Tomorrow’s Lunch Time Review