Chapter 2: Weathering & Soil

Lesson 1: Weathering

Weathering & Its Effects Weathering: The physical & chemical processes that change the Earth’s surface over time * changes Earth’s surface * this process breaks, wears, abrades, and chemically alters rocks and rock surfaces * Also changes the chemical makeup of a rock often making it easy to break rock down * Over time, will break rocks into smaller pieces, or sediments, like boulders (large rock) to clay (the most microscopic rock)

Causes of Mechanical Weathering Mechanical (Physical) Weathering: When physical processes naturally break rock into smaller pieces * The chemical makeup of a rock will not be changed by mechanical weathering Causes of Mechanical Weathering Ice Wedging Abrasion Plants Animals * Frost wedging Water enters cracks in rocks and freezes at 0 °C. Water expands as it freezes and widens the crack. Repeated freezing and thawing breaks rocks apart Grinds rock away by friction or impact When a plant grows in the crack of a rock the roots eventually grow, cracking the rock. Animals living in soil make holes in soil making it easy for water to enter causing weathering. Animals also break down rock by digging.

Types of Mechanical Weathering wetting & drying exfoliation plant roots

Chemical Weathering Chemical Weathering: Changes materials that are part of a rock into new material

Chemical Weathering Water & Chemical Weathering * most substances dissolve in water * minerals in rocks dissolve very slowly in water * when a rock dissolves in water, it breaks up into smaller parts Dissolving by Acids * quickest way for rock to dissolve * acids attract atoms away from rock minerals and dissolve them in the acids * Scientist use pH, a property of solutions, to classify chemical liquids as acidic, basic, or neutral Examples * Carbon Dioxide in the air forms a weak acid when it reacts with rain water which dissolves rock * Acid forming chemicals enter the air from natural sources such as volcanoes producing acid rain causing more chemical weathering than usual

pH 2-3 pH 4.5 pH 5.6 WEATHERING & EROSION vinegar Normal water acid rain pH 4.5 WEATHERING & EROSION

Chemical Weathering Oxidation Combines the element of oxygen with other elements and molecules oxygen needed for oxidation comes from the air adding oxygen to a substance produces an oxide 1886 today

What affects the weathering rates Environment: determines the rate at which rocks weather both type of weathering depends on water and temperature mechanical weathering requires repeated cycles of wetting and drying or freezing and thawing chemical weathering occurs most rapidly in warm, wet places type of rock also affects the weathering rate weathering is quicker on minerals with low hardness, size, and number of holes

Can weathering help plants? Water pools on the surface of rocks and attaches to the grains of soil. A greater surface area means more water, along with any substance the water contains, sticks to surfaces. Soils can hold higher concentrations of moisture and nutrients are better for plant growth

Types of Chemical Weathering Hydrolysis Oxidation Carbonic Acid

Surface Area Greater surface area increases the rate of weathering rates. Surface area is the amount of rock surfaces exposed to the atmosphere Weathering creates more surface area

Lesson 2: Weathering & Soil

What is soil? Soil: the components of soil is a mixture of weathered rock, sediments, decayed organic matter, water, and air. * changes Earth’s surface * this process breaks, wears, abrades, and chemically alters rocks and rock surfaces * Also changes the chemical makeup of a rock often making it easy to break rock down * Over time, will break rocks into smaller pieces, or sediments, like boulders (large rock) to clay (the most microscopic rock)

What is soil? Organic Inorganic Description: remains of something that was once alive Description: Materials that were never alive Examples: Leaves Dead insects Waste products Sand Silt Clay Decomposition changes once living material into dark colored organic matter. This matter helps hold nutrients in the soil

Formation of Soil Parent material: rock or sediment that weathers or forms the soil. Effect: Wind and water carry particles to a different location, Climate: the average weather of an area. Effect: amount of precipitation and temperature speeds/slows weathering Topography: the shape and steepness of the landscape. Effect: the shape of the area determines how much water reaches the soil Biota: all organisms living in a region. Effect: animals burrowing, decomposition, and wastes affects soil & rock composition Time: Soil formation is a slow process Effect: 1,000 year old soil is considered young!

Soil Horizons O HORIZON- This is the top layer of soil that is made up of living and decomposed materials like leaves, plants, and bugs. This layer is very thin and is usually pretty dark. A HORIZON- This is the layer that we call "topsoil" This layer is made up of minerals and decomposed organic matter and it is also very dark in color. This is the layer that many plants roots grow in. B HORIZON- This is the layer that we call "subsoil". This layer has clay and mineral deposits and less organic materials than the layers above it. This layer is also lighter in color than the layers above it. C HORIZON- This is the layer that we call "regolith“. This layer is made up of slightly unbroken rock and only a little bit of organic material is found here. Plant roots are not found in this layer.