Download Weathering and Erosion

WEATHERING AND SOIL
TRUE OR FALSE: THE EARTH’S
SURFACE HAS STAYED THE SAME
FOR THOUSANDS OF YEARS
TRUE OR FALSE: THE EARTH’S SURFACE
HAS STAYED THE SAME FOR THOUSANDS
OF YEARS
The Earth’s surface is always
changing!
WEATHERING
The breakdown of the materials of Earth’s
crust into smaller pieces.
WEATHERING
Two forms of weathering:
 Mechanical: is a process in which only physical
changes occur in rock materials. While there
are many types and causes of mechanical
weathering, each results in the breakdown of
rocks and sediments into smaller pieces. (does
not change the composition of the rock)
 Chemical: occurs when new substances form
due to chemical interactions between rock
materials and water, air, or biota.

WATER CAUSES WEATHERING
What evidence of
weathering do you see
in this picture?
WEATHERING: WATER

water can cause great chemical changes in
rock over long periods of time.

Turn to pg. 152 in text and read about
dissolving by acids….
WEATHERING: OXIDATION

Most iron-bearing rocks and sediments will
oxidize in the presence of atmospheric oxygen.
Rust, or iron oxide, is a product of chemical
weathering with which most students are
familiar. When any element reacts with oxygen,
a new substance called an oxide forms.
WIND CAUSES WEATHERING
Why wasn’t this mass
of land weathered
away?
What evidence of
weathering do you see
in this picture?
ICE CAUSES WEATHERING
Describe how ice
causes weathering?
PLANTS CAN CAUSE WEATHERING
WHAT AFFECTS WEATHERING RATES?

The rate at which a particular rock weathers
depends its environment and its chemical
makeup. Environmental conditions such as
frequent temperature changes and high rates of
precipitation can speed up the weathering
process. Rocks that are made up of mostly
minerals that are resistant to both chemical and
mechanical weathering, such as quartz, will
weather much more slowly than rocks that are
made up of mostly softer and more chemically
reactive minerals, such as feldspar minerals.
DISCUSSION

How does weathering break down or change
rock?
 Weathering
breaks down rock into smaller pieces
and can also change its chemical makeup.

What is the result of a rock undergoing
mechanical weathering?
 Mechanical
weathering will break a rock apart,
increasing its surface area. Smaller rocks, sand,
and clay can result from weathering.
DISCUSSION

Why is the surface area of a rock important?
 The
amount of surface area affects the rate at
which a rock will weather.

How does chemical weathering differ from
mechanical weathering?
 Mechanical
weathering breaks rock into smaller
pieces. The type of rock does not change. Chemical
weathering causes changes in the chemical
makeup of the rock.
DISCUSSION

How can pollutants create acid rain?
 Certain
chemical pollutants released into the
atmosphere dissolve in rain droplets, forming acids.

How does chemical weathering change rock?
 Chemical
weathering changes the composition of
the rock. Chemical weathering can occur as a result
of exposure to water, acid, or air.
CHALLENGE QUESTION

Why is weathering slower in cold, dry places?

Rate of weathering depends on temperature
and moisture. Cold, dry places have little water
to act as a weathering agent and do not have
the temperature changes that promote quick
mechanical weathering.
SOIL
Soil is made up of living and nonliving material
spread as a very thin layer over the entire
surface of the planet we call earth.
 Soil must provide nutrients, water, and air and
helps to support the plant.
 Soil can be thought of as a mini ecosystem,
complete with water, air, microorganisms,
worms, burrowing animals, plants, and rock
materials.

organic substances are those that are
associated with living things and contain
compounds of the element carbon.
 Inorganic components of soil are any elements
that were not once part of living organisms.
They include sediments, water, and air. The
sizes of sediments and the amount of pore
space within a soil help determine important
physical properties of soil.

FORMATION OF SOIL

Five important factors in the formation of soil
are parent material, climate, topography, biota,
and time.
FORMATION OF SOIL
1. Parent Material: the rock or sediment that
weathers to form soil.
 2. Climate: A region's climate can be described
by its average annual precipitation and its
average seasonal temperatures. The climate in
which a soil forms impacts its characteristics
and the rate at which rocks undergo chemical
weathering to form soil.

FORMATION OF SOIL
3. Topography: Topography greatly influences
how soils form. In flat landscapes, soil is not
eroded or transported as it is in steeply sloped
landscapes.
 4. & 5. Biota/Time: The action of various living
organisms—including bacteria, plants, worms,
and burrowing animals—helps speed weathering
and the decomposition of organic matter. Soil
formation is a constant, slow process. It can take
many thousands of years for a mature soil to
form as a result of weathering and
decomposition.

REMEMBER….

Soil is a combination of materials. One part of
soil is rock that has been broken down over
time by wind, water, and chemical processes.
HORIZONS

Many mature soils consist of three layers,
called horizons. The A-horizon is the topmost
layer and contains most of a soil's organic
matter—often referred to as humus. The Bhorizon has less organic matter and more clay
minerals that leach downward due to the action
of water infiltrating the soil. The C-horizon is the
lowest layer and blends into the bedrock. It
often contains larger fragments of bedrock that
are still undergoing chemical weathering.
OBSERVING AND MEASURING SOIL PROPERTIES

Some properties of soils can be observed by
using senses while other soil properties are
measured using laboratory techniques.
Properties that can be observed with the
senses include color, structure, and
consistency. Laboratory techniques are used to
measure infiltration, soil moisture, pH, fertility,
and temperature. Some properties can be both
observed and measured, such as texture.
FACTORS OF SOIL FERTILITY
Soil depth -room for roots to grow
 Availability of water
 Drainage- reduce flooding
 pH
 Minerals
 Organic matter

SOIL PROPERTIES THAT SUPPORT LIFE

Preserving a soil's fertility is a major part of soil
conservation. Nutrients in soil can take many
lifetimes to develop, but they can be depleted by
poor farming practices in only a few years.
Farmers use techniques such as crop rotation to
preserve soil fertility. Legume crops such as
peas, beans, or lentils actually enhance soil
fertility. Bacteria that grow on the roots of these
crops convert atmospheric nitrogen into a form
that can be used by plants. Use the questions
below to assess understanding of relationships
between soil properties and life.
SOIL TYPES AND LOCATIONS
Different types of soils form in different
locations. Factors that control this distribution
include differences in local climate and
latitude, rock types, topography, and biota.
 Turn to page 164 and look at the map. Note
the legend at the left.

DISCUSSION

What is the role of parent material in creating
soil?
 Parent

material is the starting material of soil.
Why do soils form rapidly in warm, moist
climates?
 Rocks
are subjected to faster rates of chemical
weathering due to warm temperatures and
chemical reactions with water.
DISCUSSION

How do biota aid in soil formation?
 Some
organisms create passages for air and water
to move into the soil, which speeds up weathering,
and others aid in the decomposition of organic
matter.

What are soil horizons?
 Soil
horizons are layers that form as soils mature.
Each layer has certain characteristics based upon
its age, its position, organic content and moisture
movement through it.
DISCUSSION

List soil properties that can be observed and
measured.
 Properties
that can be observed include color,
texture, structure, and consistency. Properties that
can be measured include texture infiltration, soil
moisture, pH, fertility, and temperature.

How are soil nutrients related to life?
 Plants
are the food source for most living organisms,
and plants depend on nutrients that they obtain
from soils. If soils do not provide adequate nutrients,
farmers have to add them to the soil before planting
crops.
DISCUSSION

Are soils the same everywhere? Why?
 Soils
vary from place to place because of the
effects of parent material, climate, biota, and
topography.