Continental Drift

Convection Currents, and

How Heat Works

Chapter 5

Convection and the MantleLets first discuss what heat is: Heat is the movement or vibration of molecules within a substance. The faster they move the hotter the substance is.

It is important to know that heat will always move from warm to cold

Types of Heat Transfer

Radiation, Conduction and Convection

Radiation- The transfer of heat energy through space. No direct contact with anything. Example: Sun and fire.

Conduction- The transfer of heat between objects that are touching. Examples: a spoon in a hot cup of tea. Your hand touching the hot handle of a pot on a stove.

Convection- The movement of heat through a fluid (gas or liquid). The movement depends on the temperature and the density of the fluid. Hot substances usually rise and cooler ones sink (Think of a hot air balloon). Examples: Heating water in a pot. Ocean currents. Movement of air through the atmosphere.

Radiation

Conduction

Convection

Drifting Continents

Alfred Wegener theorized that the continents were once all together and have since drifted apart.

This idea he called continental Drift.

He believed that about 300 million years ago all the landmasses were together in one super continent called Pangaea.

While developing his theory he looked at evidence such as land features, fossils, and evidence of climate change.

Wegener’s Theory Rejected

At the time Wegener could not show evidence of how the continents moved so his theory was rejected. The scientist at he time believed that mountains formed from the cooling of the Earth. Wegener said that if that was true then there would be mountains all over the Earth. Wegener proposed that mountains formed from the collision of continents.

We now know that the continents move by means of convection currents in the mantle.

Convection Currents in the Earth

Heat from the Earth’s core cause convection currents in the mantle just like water in a pot on the stove. Hotter substances rise to the surface and cooler ones sink, in this case magma.

Sea Floor Spreading

In the mid- 1900’s scientists used sonar to map the ocean floor’s topography. They discovered “Mid ocean ridges” which are like mountains on the sea floor.

In sea-floor spreading, the floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyer belts.

Wow, look at this mid- ocean ridge

Evidence for Sea- Floor Spreading

There are several types of evidence to support the theory of sea floor spreading including: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.

Subduction

The sea floor plunges down in what are called deep ocean trenches. This usually happens at the continental crust.

The Theory of Plate Tectonics

Section 5

Plate Tectonics

Plate- A section of the lithosphere which moves over the asthenosphere carrying pieces of crust.

Plate tectonics- the theory stating that pieces of the lithosphere are in constant motion driven by convection currents in the mantle.

Fault- Breaks in the earth’s crust where rocks have slipped past each other.

Plate Boundaries

Three Types:

Divergent- The area where two plates move apart or diverge.

Convergent- The area where two plates come together or meet.

Transform- The area where two plates move past one another in opposite directions.

Divergent boundary- where two plates move apart, most occur along mid- ocean ridges.

Rift valley- when divergent boundaries occur on land

Convergent boundary- A place where two plates come together.

Transform boundary- An area where two plates slip past on another in opposite directions.

Can you identify the different boundaries here?