Download Earth Layers and Continental Drift

Layers of Earth and
Convection Currents
How have geologists learned
about Earth’s interior structure
and what causes convection
currents in the mantle?
Earth’s Interior
Geologists have used two main types of
evidence to learn about Earth’s interior.
1. Direct evidence from rock samples (drilled from
deep inside Earth)
2. Indirect evidence from seismic waves (produced
by earthquakes; speed gives clues to the material)
Three main layers of Earth vary greatly in size,
composition, temperature and pressure. They
are the crust, mantle and core.
The Layers of Earth
Crust
Mantle
Core
• Solid rock, outer “skin”, includes dry land and ocean floor
• CRUST: 2 types: Oceanic (more dense basalt) or Continental
(less dense granite)
• Layer of solid, hot rock 40 km beneath the surface; divided into layer
• LITHOSPHERE = solid upper mantle + crust about 100 km thick
• ASTHENOSPHERE = hot, soft, “taffy-like” part; the plates move on it
when driven by convection currents; under increased pressure
• Lower Mantle = solid, extends to the core
• Outer Core (liquid/molten Fe and Ni)
• Inner Core (dense ball of solid Fe and Ni)
• Movement of liquid outer core creates Earth’s
magnetic field
Layers of Earth
Two Types of Crust
Oceanic Crust
Continental Crust
Rock Type
Basalt
Granite
Color
Dark
Light
Composition
Low Si, High Fe
High Si, Low Fe
Density
High
Low
6-7 km, avg.
40 km, avg.
Floats lower in the mantle
– form basins that fill
with water
Floats higher in the
mantle
Average
Thickness
Depth
(general)
Convection and the Mantle
Heat Transfer: 3 Types are...
Radiation – transfer of energy through empty space, has no
direct contact between the heat source and an object (Ex:
sunlight warming Earth’s surface)
Conduction – heat transfer by direct contact of particles of
matter (Ex: metal spoon heating up in a pot of hot soup)
Convection – transfer of heat by the movement of a heated fluid
(includes liquids and gases); Heat transfer is caused by
differences in temperature and density within a fluid (Ex: Water
on a stove – water heats at the bottom of the pan, becomes less
dense and rises; away from the heat source the water cools,
becomes more dense and sinks; the process begins again) This is
a Convection Current, or flow that transfers heat.
Density – measure of how much mass there is in a volume of a
substance
Convection Currents in the Mantle
The heat source is the Earth’s core and from the
mantle itself. These currents have been acting
like a conveyor belt moving the lithosphere
above for the past four billion years