The Rock Cycle

This section addresses, in whole or in part, the following Georgia GPS standard(s):

S6E5c. Describe processes that change rocks and the surface of the Earth.
S6E5e. Explain the effects of physical processes (plate tectonics, erosion, deposition, volcanic eruption, gravity) on geological features including oceans (composition, currents, and tides).
S6CS5a. Observe and explain how parts are related to other parts in systems such as weather systems, solar systems, and ocean systems including how the output from one part of a system (in the form of material, energy, or information) can become the input to other parts.

This section addresses, in whole or in part, the following Benchmarks for Scientific Literacy:

The formation, weathering, sedimentation, and reformation of rock constitute a continuing "rock cycle" in which the total amount of material stays the same as its forms change.
Sediments of sand and smaller particles (sometimes containing the remains of organisms) are gradually buried and are cemented together by dissolved minerals to form solid rock again.
Sedimentary rock buried deep enough may be reformed by pressure and heat, perhaps melting and recrystallizing into different kinds of rock. These re-formed rock layers may be forced up again to become land surface and even mountains. Subsequently, this new rock too will erode. Rock bears evidence of the minerals, temperatures, and forces that created it.
The earth is mostly rock. Three-fourths of its surface is covered by a relatively thin layer of water (some of it frozen), and the entire planet is surrounded by a relatively thin blanket of air. It is the only body in the solar system that appears able to support life. The other planets have compositions and conditions very different from the earth's.
Rock is composed of different combinations of minerals. Smaller rocks come from the breakage and weathering of bedrock and larger rocks. Soil is made partly from weathered rock, partly from plant remains-and also contains many living organisms.

This section addresses, in whole or in part, the following National Science Education Standards:

Some changes in the solid earth can be described as the "rock cycle." Old rocks at the earth's surface weather, forming sediments that are buried, then compacted, heated, and often recrystallized into new rock. Eventually, those new rocks may be brought to the surface by the forces that drive plate motions, and the rock cycle continues.

The rock cycle explains how one type of rock can be transformed into another in nature.

View the diagrams of rock cycle below.

U.S. Geological Survey public domain image of the rock cycle.

Here is another diagram of the rock cycle. How is it like the one above? How is it different?

Magma cools and crystallizes to form igneous rock.
Igneous rock undergoes weathering (or breakdown) to form sediment. The sediment is transported and deposited somewhere (such as at the beach or in a delta, or in the deep sea).
The deposited sediment undergoes lithification (the processes that turn it into a rock). These include cementation and compaction.
As the sedimentary rock is buried under more and more sediment, the heat and pressure of burial cause metamorphism to occur. This transforms the sedimentary rock into a metamorphic rock.
As the metamorphic rock is buried more deeply (or as it is squeezed by plate tectonic pressures), temperatures and pressures continue to rise. If the temperature becomes hot enough, the metamorphic rock undergoes melting. The molten rock is called magma. This completes the cycle.

Now if you look at the processes going on in the middle of the diagram, note that:

Any rock type can undergo weathering (breakdown) to form sediment, followed by transportation and deposition of the sediment. Both metamorphic and sedimentary rocks can undergo weathering.
Igneous rocks can undergo metamorphism (as a result of heat and pressure) to form metamorphic rocks.

Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA

Page created February 16, 2005
Links updated October 13, 2008