Download rock cycle_pangea - Northside Middle School

Many forces cause the surface of the Earth to change over time. However,
the largest force that changes our planet’s surface is the movement of
Earth's outer layer through the process of plate tectonics. This process
causes mountains to push higher and oceans to grow wider.
As shown in this diagram, the rigid outer layer of the Earth, called the
lithosphere, is made of plates which fit together like a jigsaw puzzle.
These solid but lightweight plates seem to "float" on top of a more
dense, fluid layer underneath.
Motions deep within the Earth carry heat from the hot interior to the
cooler surface. These motions of material under the Earth's surface cause
the plates to move very slowly across the surface of the Earth, at a rate
of about 2 inches per year. There are several different hypotheses to
explain exactly how these motions allow plates to move.
Interesting things happen at the edges of plates. Subduction zones form
when plates crash into each other, spreading ridges form when plates pull
away from each other, and large faults form when plates slide past each
other.
Subduction Zone
Spreading Ridge
Faults
This map illustrates the break-up of the supercontinent, Rodinia, which formed 1100
million years ago. The Late Precambrian was an "Ice House" World, much like the
present-day.
Animals with hard-shells appeared in great numbers for the first time during the
Cambrian. The continents were flooded by shallow seas. The supercontinent of
Gondwana had just formed and was located near the South Pole.
By the Devonian the early Paleozoic oceans were closing, forming a "prePangea". Freshwater fish were able to migrate from the southern hemisphere
continents to North America and Europe. Forests grew for the first time in the
equatorial regions of Artic Canada.
Vast deserts covered western Pangea during the Permian as reptiles spread
across the face of the supercontinent. 99% of all life perished during the
extinction event that marked the end of the Paleozoic Era.
The supercontinent of Pangea, mostly assembled by the Triassic, allowed land
animals to migrate from the South Pole to the North Pole. By the end of the
Triassic Era, Pangea began to split apart.
By the Early Jurassic, south-central Asia had assembled. A wide Tethys ocean
separated the northern continents from Gondwana. Though Pangea was intact, the
first rumblings of continental break up could be heard. Dinosaurs spread across
Pangea.
The supercontinent of Pangea began to break apart in the Middle Jurassic. In the
Late Jurassic the Central Atlantic Ocean was a narrow ocean separating Africa from
eastern North America. Eastern Gondwana had begun to separate form Western
Gondwana.
During the Cretaceous the South Atlantic Ocean opened. India separated from
Madagascar and raced northward on a collision course with Eurasia. Notice that
North America was connected to Europe, and that Australia was still joined to
Antarctica.
The bull's eye marks the location of the Chicxulub impact site. The impact of a 10
mile wide comet caused global climate changes that killed the dinosaurs and many
other forms of life. By the Late Cretaceous the oceans had widened, and India
approached the southern margin of Asia.
50 - 55 million years ago India began to collide with Asia forming the Tibetan
plateau and Himalayas. Australia, which was attached to Antarctica, began to
move rapidly northward.
20 million years ago, Antarctica was coverd by ice and the northern continents were
cooling rapidly. The world has taken on a "modern" look, but notice that Florida and
parts of Asia were flooded by the sea.
When the Earth is in its "Ice House" climate mode, there is ice at the poles. The
polar ice sheet expands and contacts because of variations in the Earth's orbit. The
last expansion of the polar ice sheets took place about 18,000 years ago.
If we continue present-day plate motions the Atlantic will widen, Africa will collide
with Europe closingthe Mediterranean, Australia will collide with S.E. Asia, and
California will slide northward up the coast to Alaska.
The next Pangea, "Pangea Ultima" will form as a result of the subduction of the
ocean floor of the North and South Atlantic beneath eastern North America and
South America. This supercontinent will have a small ocean basin trapped at its
center.
Rocks are not all the same!
The three main types, or classes, of rock are sedimentary, metamorphic,
and igneous and the differences among them have to do with how they
are formed.
Sedimentary
Sedimentary rocks are formed from particles of sand, shells,
pebbles, and other fragments of material. Together, all these
particles are called sediment. Gradually, the sediment
accumulates in layers and over a long period of time hardens
into rock. Generally, sedimentary rock is fairly soft and may
break apart or crumble easily. You can often see sand,
pebbles, or stones in the rock, and it is usually the only type
that contains fossils.
Examples of this rock type include conglomerate and
limestone.
Metamorphic Rocks
Metamorphic rocks are formed under the surface of the
earth from the metamorphosis (change) that occurs due
to intense heat and pressure (squeezing). The rocks
that result from these processes often have ribbonlike
layers and may have shiny crystals, formed by minerals
growing slowly over time, on their surface.
Examples of this rock type include gneiss and marble.
Igneous
Igneous rocks are formed when magma (molten rock
deep within the earth) cools and hardens. Sometimes the
magma cools inside the earth, and other times it erupts
onto the surface from volcanoes (in this case, it is called
lava). When lava cools very quickly, no crystals form and
the rock looks shiny and glasslike. Sometimes gas
bubbles are trapped in the rock during the cooling
process, leaving tiny holes and spaces in the rock.
Examples of this rock type include basalt and obsidian.
Rocks take different forms at different times. A long time ago our earth was very volcanic. As these
volcanoes cooled and vast oceans swept over the earth, the cooled lava was broken or crushed into small
pieces. These small pieces were cemented together to become sedimentary rocks. These rocks were
buried and the heat and pressure changed them into metamorphic rocks. They might even have melted
and become igneous rocks once more. As you can tell a rock may change many times and the rock you
hold today may look entirely different to someone a long time from now.
Look at the diagram below and see if you can trace a rock through the rock cycle.
http://www.scotese.com/earth.htm