Earth’s Structure Notes
Stratigraphic Superposition-this means that each layer of
rock in the earth is older than the layer above it.
Fossils-recognizable remains or body impressions of an
organism that lived in the past.
The earth is about 4.6 billion years old.
The crust is the outermost layer of the earth. It is the
thinnest layer of the earth. The thickest layers of the
crust are usually around mountain ranges.
The mantle is just below the crust. This means it is more
dense than the crust.
The lower mantle is molten, meaning the rocks are so hot
that they flow like magma.
The core of the Earth is at the center and is the most
dense.
The core is made of iron and nickel.
The crust is broken into two types: continental and
oceanic.
Continental crust is the land where we live and oceanic
crust is the part of the crust underneath the oceans.
Scientists believe that about 200 million years ago all the
continents were attached as a supercontinent called
“pangeae”
Eventually the continents broke apart and began drifting
away from each other. This is called “continental drift”.
The reason for continental drift is probably “convection
currents” of rock and magma that flow in a circular
pattern below the crust.
Below the crust, the mantle breaks apart into thick slabs
of rock called tectonic plates.
These plates move in three ways:
1. Divergent boundaries-two plates move away from
each other.
2. Convergent boundaries-two plates move toward
each other.
3. Transform boundaries-Two plates slide past each
other.
A fault is a crack in the earth’s crust. Faulting occurs
when bodies of rock slide past each other with
vertical or horizontal movement at a plate boundary
often resulting in earthquakes.
A volcano is a mountain formed from lava and rocks
made from materials that have emerged from inside
the earth.
Magma is liquid material inside the earth.
Volcanoes typically appear at convergent plate
boundaries.
Magma reaches the earth’s surface through a hole
called a vent.
When magma reaches the earth’s surface, we call it
lava.
When lava cools and hardens, it turns into igneous
rock.
Rock Cycle
There are three types of rocks: igneous,
sedimentary, and metamorphic
Igneous rocks are formed from melted magma or
lava
There are two types of igneous rocks: intrusive and
extrusive.
Intrusive igneous rocks are formed from magma in
the earth
Extrusive igneous are formed from lava on the
earth’s surface.
Sedimentary rocks are formed when little particles
of weathered igneous rocks begin to stick together
as they tumble down streams, rivers, etc.
Metamorphic rocks are formed when the actual
structure of a rock is changed by heat and pressure
in the earth.