Transcript The Rock Cycle

Rocks and Rock Cycle
Mrs. Reese
Do rocks change over time?
The Earth is 4 billion years old and people only
live for 100 years so most people do not get to
see very many dramatic changes to their
surroundings. The evidence of change is
found in many of our landforms made from
rock. Change happens over many years
(hundreds, thousands, and even millions of
years.)
WATER EROSION
WIND EROSION
VOLCANIC ACTIVITY
What is a Rock?
• A rock is a solid material made up of one or
more minerals or other substances such as
once-living organisms that occurs naturally.
Why are rocks important?
Glimpse at the past…
Rocks are a fascinating way to discover
information about the history of the Earth.
The Cambrian period (490 million years ago)
was characterized by an interesting diversity
of life in the seas. Life had not yet evolved
upon land. The highest forms of life existing at
this time were the trilobites (marine
arthropod), which reached lengths up to two
feet.
How do geologist classify rocks?
• Geologist can classify rocks based on various
characteristics such as color, texture,
arrangement of grains, composition (what
minerals it has), density, and how the rock
forms.
How many groups of rocks are
there?
• There are THREE main groups: Igneous,
Metamorphic, and Sedimentary.
How are igneous rocks formed?
• Igneous rocks are formed from molten
magma or lava cooling and hardening. The
word, igneous means "fire".
What happens when the magma
cools slowly or quickly?
• If the magma cools and hardens inside the
earth it is called "intrusive" igneous rock.
These rocks cool slowly and have large
crystals.
• When the lava comes out of the earth's crust
through a volcano, it is called "extrusive“
igneous rock. If it cools off quickly, the crystals
that form are very small, the rock will take a
glassy appearance, or the rock will be porous.
PUMICE
(EXTRUSIVE)
OBSIDIAN
(EXTRUSIVE)
GRANITE
(INTRUSIVE)
Weathering
All rocks are subject to weathering.
Weathering is anything that breaks the rocks
into smaller pieces or sediments. This can
happen by the forces of wind, rain, chemical
reactions, and freezing water.
Sediment Sizes
Erosion
• The combination of weathering and
movement of the resulting sediments is called
erosion.
Deposition
• The sediments that form from these actions
are often carried to other places by the wind,
running water, and gravity. As these forces
lose energy the sediments settle out of the air
or water. As the settling takes place the rock
fragments are graded by size. The larger
heavier pieces settle out first. The smallest
fragments travel farther and settle out last.
This process of settling out is called
deposition.
Compaction and Cementation
Compaction occurs after the sediments have
been deposited. The weight of the sediments
squeezes the particles together. As more and
more sediments are deposited the weight on
the sediments below increases. Waterborne
sediments become so tightly squeezed
together that most of the water is pushed out.
Cementation happens as dissolved minerals
become deposited in the spaces between the
sediments. These minerals act as glue or
cement to bind the sediments together.
Clastic Sedimentary Rocks
The most common set of sedimentary rocks consist of
the granular materials that occur in sediment: mud and
sand and gravel and clay.
Sand is made of quartz, and mud is made of clay
minerals. As these sediments are steadily buried over
geologic time, they get packed together under pressure
and low heat, not much more than 100°C. In these
conditions the sediment is cemented into rock: sand
becomes sandstone and clay becomes shale. If gravel or
pebbles are part of the sediment, the rock that forms is
conglomerate.
Organic Sedimentary Rocks
Sediment can form in the sea as microscopic
organisms. Dead plankton steadily shower their
dust-sized shells onto the seafloor, where they
accumulate in thick layers. That material turns to
two more rock types, limestone (carbonate) and
chert (silica).
Another type of sediment forms where dead plant
material builds up into thick layers. With a small
degree of compaction, this becomes peat; after
much longer and deeper burial, it becomes coal.
Chemical Sedimentary Rocks
Ancient shallow seas sometimes allowed large
areas to become isolated and begin drying up.
In that setting, as the seawater grows more
concentrated, minerals begin to come out of
solution (precipitate), starting with calcite,
then gypsum, then halite. The resulting rocks
are limestone, dolomites, gypsum, and rock
salt.
SHALE (Sedimentary)
FORMED FROM CLAY-IT HAS VERY FINE GRAINS.
CONGLOMERATE (Sedimentary)
COARSE GRAINS
SILTSTONE (Sedimentary)
MADE FROM SILT AND HAS VERY FINE GRAINS.
SANDSTONE (Sedimentary)
MADE FROM SAND AND HAS MEDIUN COARSE GRAINS.
LIMESTONE (Sedimentary)
MADE FROM CALCITE(CHALK) AND HAS VERY FINE GRAINS.
COAL (Sedimentary)
MADE FROM DEAD PLANT SEDIMENTS AND HAD FINE GRAIN.
GYPSUM (Sedimentary)
MADE FROM EVAPORATION OF WATER WITH CONCENTRATED
MINERALS.
How are metamorphic rocks
formed?
Metamorphic rocks are formed when other
kinds of rocks are changed by great heat and
pressure inside the earth. The word
"metamorphic" means changed.
Think of metamorphic rocks as recycled rocks.
When igneous, sedimentary or even
metamorphic rocks get buried deep beneath
the surface of the earth, over millions of years
the heat and pressure inside the earth change
them into another rock.
CHANGED
SLATE
PHYOLLITE
CHANGED
GRANITE
GNEISS
CHANGED
PERIDIOTITE
SOAPSTONE
Rock Cycle
• The rock cycle is a continuous cycle in which
forces inside the Earth and at the surface
build, destroy, and change the rocks in the
crust.
Rock Cycle