ROCK CYCLE

IGNEOUS ROCK Formed when –magma cools underground EX: granite –Or above ground EX: lava rock/pumice

SEDIMENTARY ROCK Repeated settling of eroded soil. Compressed layer by layer until it turns into rock. Ex: shale, limestone

METAMORPHIC ROCK Sedimentary or igneous rock that has morphed into another type of rock Due to intense pressure or heat EX: schist, gneiss

SOIL

What is soil? The loose covering of broken rock particles and decaying organic matter (humus) covering bedrock.

Why is soil important? Grow food Wood for building Plants provide oxygen Filter pollutants

How is soil created? Rock is chemically and physically weathered. Bacteria, fungi, lichens, & insects live in weathered rock. These organisms die and add nutrients to weathered rock. As soil builds, larger organisms can move in and colonize. Takes 100’s of years to create a few cm of soil.

What is a soil profile? Vertical sequence of soil layers (horizons). O Horizon- vegetation/ leaf litter on top of soil A Horizon- dark-colored thin layer; rich in organic matter; humus B Horizon- thick layer of subsoil; may be red or brown; clay based soil C Horizon- contains weathered parent rock; larger particles of rock; no organic matter R Horizon- unaltered parent bedrock O horizon R horizon

TYPES OF SOIL Polar soil –Form at high elevations & high altitudes –No distinct horizons- soil too thin –Under top few inches of soil, ground is permanently frozen- PERMAFROST.

Temperate soils –Vary depending on rainfall & type of vegetation –Tropical Grasslands- very thick, rich, humus –Forests- thinner, less fertile clay soil –Prairies- less rain, so soil not as thick, but still fertile.

Desert soils –Very thin A horizon –Very little organic matter –High in minerals –Soil is usually light colored and coarse textured.

Tropical soils –Intensely weathered due to high precipitation and temp. –Very little humus & very few nutrients –High concentrations of iron- when oxidizes causes characteristic red color.

SOIL TEXTURES Size of particles determines –Water holding capacity –How compacted soil is –Ability to support plant Sand- larger particles Silt- smaller particles Clay- smallest particles Loam- equal mix of sand, silt, and clay

SOIL FERTILITY Measure of how well soil can support plant life. Factors that affect fertility of soil: –Level of minerals & nutrients –Level of bacteria –Amount of precipitation –Topography –Acidity of soil

Farmers may adjust level of fertility by –Adding commercial fertilizers

–Crop rotation- alternating corn crop with legume (peas, beans, clover) to add nutrients back to soil

–Limestone- reduces acidity of soil

–Organic fertilizers- compost, mulch, peat moss

SOIL CONSERVATION Soil is easily eroded. Methods to prevent erosion include:

Contour Farming- plowing along slope instead of up and down it. Furrows btwn rows of crops collect water.

Terracing- series of platforms are built into slopes. Effective with steep slopes, slows water flow.

Shelter Belts- rows of trees planted along outer edges of s creating a windbreak to prevent wind erosion.

Strip-Cropping- Farmers plow so that plowed strips are separated by planted strips. Roots of planted strips hold soil in place.

Reduce Grazing Permits Put up fencing –Animals cannot compact and destroy plants