LAYERS OF THE EARTH
There are three main layers of the Earth:
(1) relatively thin, rocky crust
(2) thick silicate mantle of hot plastic rock
(3) dense core-composed mainly of iron; liquid outer core (huge), solid crystalline
inner core (small)
By careful mapping of the patterns of many earthquakes that travel to different
depths, seismologists have peeled away the Earth’s outer layers and looked at
various levels within it.
This is due to the different ways rock layers of different density and
stiffness propagate the waves at different speeds.
The Earth’s internal structure is determined by the varying velocity of
earthquake waves. (two kinds: push-and-pull, shake)
Two major types of terrain on Earth: high, dry continents and low, wet floor
Wegner came up with the theory of moving continents.
He based his concept of
continental drift not only on the similar shapes of the present continental edges
but also the striking match of certain rocks, geological formations, fossils along
the borders of continents on opposite sides of the Atlantic.
Concluding that, all the continents were once, 200 million years ago, part of a
single landmass, Pangea, that drifted apart due to plate tectonics.
Sea floor spreading: new sea floor is forced at a rift in the mid-ocean ridge,
turning cold and heavy as it spreads away from its source in two directions; the
sea floor eventually sinks and disappears in a deep-ocean trench, where it is
consumed, Its material is then recycled and born again as new floor emerges from
The continents are implanted with moving plates, driven by heat from below, and
continental drift is a consequence of the motion of plates carried along by the sea-
The effects of continental drift account for most of our world’s familiar surface
phenomena, such as mountains, earthquakes and ocean basins.
The ozone layer is created by the sun’s ultraviolet rays
The ozone layer is a layer of O3, which blocks radiation from the Sun.
It protects us by absorbing most of the Sun’s ultraviolet emission and keeping its
destructive rays from reaching the ground. If there were no ozone shield, plants,
animals, and humans could not even exist on the land.
We punch holes through the ozone layer with chemicals used in our everyday