The Rock Cycle and Soils

Chapter 4

Addendum

What is a Rock?

Solid mass of minerals or mineral–like matter

1. Three types of rocks:

a. Igneous Rock (from “ignis” in Latin, meaning fire)b. Rock begins as liquid (magma) beneath the earth’s surface, and form when magma/lava cool and hardens.

Igneous rock begins as magma.

(1) Rocks that forms from lava (magma on earth’s surface) are extrusive.

(a) Rocks that form from magma cooled under the surface are intrusive

http://geology.com/

How are magma & lava the same, and how are they different?

Same

Both terms used to describe molten rock

Composition can be the same

Different

Magma is melted material beneath the Earth’s surface

Lava is melted material at the Earth’s surface

b. Sedimentary Rocks(1) Form when sediments become

compacted and cemented together.

They are called clastic sedimentary rocks.

Explain Compaction & Cementaion

Compaction- process that squeezes sediments together

Cementation- occurs when dissolved minerals are deposited/distributed in the tiny spaces among sediments

Or

(2) Compounds are chemically bonded to form rocks. They are called chemical sedimentary rocks.

Rock Salt

Salt flats in Turkey

Salt Flats Boneville, Utah

Gypsum

Or

(3) Compounds are passed through, or used by an organism then form rock. They are called organic sedimentary rocks.

coal

Sedimentary rocks are a result of…

Weathering

Erosion and deposition

Compaction and Cementation

c. Metamorphic rock (“meta meaning change, “morph” meaning form)

(1). Formed when chemical reactions, heat, pressure, radioactive decay or friction change existing rock into a rock with different chemical and physical properties.

(2) Temperatures increase and the rock becomes flexible (not

melting). The atoms rearrange themselves to more heat tolerant materials become denser (more atoms per unit area).

Marble

Slate

Gneiss

(3) Rocks can undergo metamorphism (change) two main ways

(a) Contact metamorphism- when rock comes into contact with magma in the ground and the heat from the magma will change the composition of the rock and creating a new metamorphic rock

(b) Regional Metamorphism- when enormous pressure builds up in rock, that is buried underground and the temperature increases (due to the pressure). This extreme pressure and heat causes the rock to become deformed and chemically changed forming new metamorphic rock

2. Recyling Rock a. Earth is very dynamic – changes occurring all the time. (Ex. Movement of tectonic plates, volcanoes, mountain formation, weathering) which affect rock composition, size, shape, and location.

b. There is no definite sequence to the process.

c. Major factors that cause change: temperature, pressure, friction, weathering, time, and composition of rock.

Granite weathering to clay > particles travel down stream – settling > into layers cementation > sedimentary (shale) –heat and pressure > metamorphic (slate) where could it go from here?

Example of Rock Cycle:(tables in text pages 74, 79, and 84)

Shells containing Calcite (CaCO3) weathering to calcite particles > particles settling on sea floor into layers > cementation and compaction > sedimentary (Chalk, Limestone) –heat and pressure > metamorphic (Marble) where could it go from here?

Example of Rock Cycle:

Granite heat and pressure > metamorphic (gneiss) where could it go from here?

Example of Rock Cycle:

Plant matter Decomposition and layering Peat compaction and cementation Lignite Bituminous coal heat and pressure > metamorphic Anthracite coal where could it go from here?

Example of Rock Cycle:

3. Soil Formation a. Results from the

continuous weathering (mechanical and chemical) of rocks (into smaller and smaller pieces) combined with living organisms, water, air, and decaying organic material (humus).

b. Parent Rock is the bedrock from that when weathered breaks down and begins the process of soil formation. Takes 100’s to 1000’s of years to form 10cm of soil.

c. Extremely important to organisms, this is the source of nutrients and water for all living things. (absorbed by plants ›plants eaten by animals › plants and animals die and decay › nutrients returned to soil)

d.Soil Composition (1) 80% are rock

particles. There are 3 basic particle sizes.

(a)Sand (0.05mm to 2mm size) – good drainage and aeration, doesn’t store water well; unsuitable for plants

(b) Silt (0.002mm to 0.05mm size)

(c) Clay (0.002mm and smaller) – hold water well, doesn’t drain well, few air spaces; unsuitable for plants

(2)Percentage of the 3 particle sizes in the mixture determines the soil type and characteristics of soil.

Ex. sandy at the beach, red clay in the piedmont of NC.

(3) Loamy soil has equal parts of all 3 particle sizes and is the optimal soil type

The Soil Texture Triangle

e. Soil Horizons / Soil Profile

(1) As weathering progresses, distinct soil

layers form. The more time involved the more mature the soil. Take’s 1000’s of

years to form mature soil.

(2) Layers: (a)O layer – organic

material (Ex. dead leaves, twigs)

(b) A layer – upper layer / topsoil

i.Dark colored; most fertile ii.Where most organisms

exist and composed of humus

(c) B layer – subsoil i. Mostly clay ii. 100,000 years to

form

(d) C layer – partially weathered bed rock and extends to parent rock

(e) R layer – bed rock

f. Causes of Soil Mismanagement

(1) Plants planted in the wrong climate and location, can increase the rate of erosion_(topsoil washing away)

(2) Clearing vegetation for construction, mining, agriculture on land and in bodies of water

(3) Overuse of fertilizers and pesticides adding chemicals to the soil

(4) Pollution from factories and automobiles (contribute to sulfuric acid and carbonic acid content of the soil)

(5) Compaction from cars, farm animals, machines.

Review Questions:

1. Explain why ultimately YOU and your health are related to the soil.

Because our food is grown in soil.

2. You are planting a vegetable garden in your back yard and you live in the Piedmont of North Carolina. What will you want to do to prepare the soil for your vegetable garden and why?

Our soils are heavy clay. Organic matter needs to be added to the soil to loosen it up and make it more fertile.

3. Why is soil considered a potentially renewable resource and therefore important to conserve? Give several reasons and one possible method of conservation of soil.

It takes many years for soil to form from parent rock. Soil should be conserved because it takes to long to be replenished and we need it to grow our food.

Soil Lab

Use auger to obtain soil sample

Determine the composition of each soil horizon in your sample using the feel method and soil pyramid

Create a soil profile

Write a lab report and correctly identify the soil type in each horizon.