THE ROCK CYCLE – THE ROCK CYCLE –

It has no start. It has no start. It has no finish.It has no finish.

Rocks that get broken up, Rocks that get broken up, This cycle will replenish!This cycle will replenish!

The Earth is active. Even more so The Earth is active. Even more so than an antsy 6than an antsy 6thth-grader! In fact, as -grader! In fact, as you are reading this:you are reading this:

Volcanoes are erupting. Volcanoes are erupting. Earthquakes are shaking. Earthquakes are shaking. Mountains are being pushed Mountains are being pushed up and being worn down. up and being worn down. Rivers are carrying sand Rivers are carrying sand and and mud to the sea. mud to the sea. Huge slabs of Earth’s surface, Huge slabs of Earth’s surface, called tectonic plates, are called tectonic plates, are slowly moving – about as fast slowly moving – about as fast as your fingernails grow. as your fingernails grow.

The three main types of The three main types of rock in the Earth’s crust rock in the Earth’s crust are are igneous, sedimentary, igneous, sedimentary, and metamorphic. and metamorphic. They are They are constantly changing. Rocks constantly changing. Rocks change shape and change shape and composition in a variety of composition in a variety of ways. ways.

The The rockrock cyclecycle is the process by is the process by which one rock type changes into which one rock type changes into another.another.

Processes that change rock:Processes that change rock:

* * Weathering and Erosion – Weathering and Erosion – Weathering is the process which Weathering is the process which breaks rocks into smaller bits. breaks rocks into smaller bits. Erosion is the removal and Erosion is the removal and transport of material by wind, transport of material by wind, water, or ice. water, or ice.* * Deposition – Deposition – The process by The process by which material is dropped or which material is dropped or settles; makes layers that lead to settles; makes layers that lead to formation of sedimentary rock formation of sedimentary rock

* * Heat and Pressure - Heat and Pressure - Earth Earth movements can push all types of movements can push all types of

rock deeper into the Earth. These rock deeper into the Earth. These

rocks are then subjected to rocks are then subjected to massive temperatures and massive temperatures and pressures causing the crystalline pressures causing the crystalline structure and texture to change. structure and texture to change. Yields metamorphic rocks. Yields metamorphic rocks.

* * Cooling – Cooling – Leads to the formation of Leads to the formation of igneous rocks that contain minerals igneous rocks that contain minerals randomly arranged in crystals. The randomly arranged in crystals. The size of the crystals tells you whether size of the crystals tells you whether the rock cooled slowly or quickly the rock cooled slowly or quickly Remember: Remember: Big crystals Big crystals = cooled slowly = cooled slowly underground = underground = IntrusiveIntrusive Small crystals Small crystals = cooled quickly = cooled quickly after a volcanic eruption = after a volcanic eruption = ExtrusiveExtrusive

It should be noted that the It should be noted that the rock rock cyclecycle is a is a modelmodel used by scientists used by scientists to describe rocks’ changes on the to describe rocks’ changes on the Earth. Rocks rarely undergo the Earth. Rocks rarely undergo the complete process shown in the complete process shown in the traditional diagrams. Sedimentary traditional diagrams. Sedimentary rocks can become igneous rocks, rocks can become igneous rocks, and metamorphic rocks can become and metamorphic rocks can become sedimentary rocks. It can take sedimentary rocks. It can take billions of years for changes to billions of years for changes to occur! occur!

So, the next time you pick up a So, the next time you pick up a rock, just think, you’re holding a rock, just think, you’re holding a part of Earth’s geologic history. part of Earth’s geologic history. And that And that totally totally rocksrocks!!

Credits:Credits:

http://www.moorlandschool.co.uk/earth/http://www.moorlandschool.co.uk/earth/rockcycle.htmrockcycle.htm

Holt Science & Technology Earth Science. Texas: Holt, Rinehart and Winston, 2001.

http://library.thinkquest.org/J002289/