The Rock Cycle Sixth Grade Science Unit 2 Lesson 7

The Earth began as a mass of molten material that cooled to form igneous rock

That igneous rock weathered to form Earth’s landscape.

Then the plate movements we’ve been learning about began to take their turn in shaping Earth’s surface.

In Time, the ROCK CYCLE IS “BORN.”

Igneous rock is made… Igneous rock is exposed to mechanical and chemical weathering Igneous rock becomes gravel, pebbles, sand, silt, clay Over time, layers of these materials are made and cover Earth’s crust Until they become…

…SEDIMENTARY ROCK. Sedimentary rock can contain fossil remains of plants and animals Sediment created by weathering, and the fossil record it holds, have made it possible for scientists to piece together what we know about the history of Earth.

Sedimentary Rock, over time, is subjected to heat and pressure… It then becomes some type of METAMORPHIC ROCK

Metamorphic Rock, over time, can then be subjected to heat and pressure as in a subduction zone. It will then melt to become magma Magma will eventually either cool or go to the surface in some sort of eruption Then the rock material is back to IGNEOUS ROCK

Rock Cycle

Formation of Igneous Rock Scoria & Pumice Basalt Obsidian

Igneous Rock Pumice Basalt Scoria

IGNEOUS ROCK Scoria and pumice are violently shot out of a volcano by force and pressure below ground. They are very light weight because they cool with lots of air bubbles. Pumice is the lightest and will float in water.

Basalt is formed by lava that cools slowly outside the volcanic eruption.

Obsidian forms from lava that cools very fast outside the volcanic eruption.

When magma cools underground, it cools more slowly than magma cooling above ground.

Igneous rock cools at different rates; slow cooling forms large crystals & fast cooling forms small or no crystals

This is most often the combination of rocks we find around us.

All of these processes are going on at the same time on all of the materials on Earth’s crust..

Igneous rock weathers to sediments and the sediments form sedimentary rocks. Heat and pressure transform sedimentary rock into metamorphic rock. Sedimentary & metamorphic rock is melted to form igneous rock. Weathering occurs continuously throughout the cycle.

The Rock Cycle is caused by : Heat Pressure Weathering

It’s A Cycle That Continues to Repeat Itself Over & Over

Weathering

Weathering’s Connection 1. Precipitation falls on part of Earth’s crust 2. Water weathers crust materials 3. Weathered materials result in erosion 3. Eroded crust materials transported to body of water 4. Transported materials fall out of suspension 5. Materials form a layer on the bottom of water 6. Materials may be affected by vulcanism 7. Tectonic forces move material to subduction zone 8. Melted material forced again to surface by eruption CYCLE REPEATS

Granite Weathering: sometimes erosion creates interesting shapes.

Granite Tombstones Weather: Although it’s very hard, names carved into granite will disappear due to weathering.

Weathering & Erosion Leave Harder Materials Behind

Soil Particles Eroded To Expose Root Systems

Silt and Eroded Materials Transported by Water

Sediments Suspended In Water

These Were Igneous Intrusions underground until weathering exposed them.

Sedimentary Layers

Sediments Will Fill In Low Areas

Weathering Is Also Done By Wind.

Fossils Are Preserved In Sedimentary Layers

Sedimentary Layers of Rock Scientists have gotten the information that we have explaining the geologic history of the Earth from sedimentary layers deposited over thousands/millions of years. Sedimentary is the only type of rock that preserves fossilized evidence of previous life on Earth.

Gneiss (metamorphic) Granite (igneous)

Metamorphic Rock Granite is an igneous rock that is changed to gneiss, a metamorphic rock, when subjected to enough heat and pressure.

Shale (sedimentary) turns to Slate (metamorphic) with heat & pressure

HOMEWORK: Make a detailed, labeled diagram of the rock cycle that explains how each type of rock is created.