© Phil Degginger / Alamy- Derelict lands degraded by mining can be restored by filling
in and grading the land to its natural contours and then
planting vegetation to hold the soil in place.
4 Soil Properties and Processes 309
- Soil is the uppermost layer of Earth’s crust and supports
terrestrial plants, animals, and microorganisms. Soil is formed
from parent material—rock that is slowly fragmented into
small particles through biological, chemical, and physical
weathering processes. - Soil is composed of mineral particles, organic matter, water,
and air. Soil horizons are the horizontal layers into which
many soils are organized, from the surface to the underlying
parent material. - Soil organisms provide ecosystem services such as
maintaining soil fertility and preventing soil erosion. Soil
organisms carry out nutrient cycling, the pathway of
nutrient minerals or elements from the environment through
organisms and back to the environment.
5
Soil Problems and Conservation 312- Sustainable soil use is the wise use of soil resources,
without a reduction in the amount or fertility of soil, so soil is
productive for future generations. Soil used in a sustainable
way renews itself by natural processes year after year. - Water, wind, ice, and other agents cause soil erosion, the
wearing away or removal of soil from the land. Soil erosion
reduces fertility because essential minerals and organic
matter are removed. Erosion causes sediments and pesticide
and fertilizer residues to pollute nearby waterways. - Good soil conservation practices promote sustainable soil use.
In conservation tillage, residues from previous crops partially
cover the soil to help hold it in place until newly planted seeds
are established. Crop rotation, the planting of different crops
in a field over a period of years, decreases the insect damage,
disease, and mineral depletion that occur when one crop is
grown continuously. Contour plowing, which matches the
natural contour of the land, helps control erosion of land with
variable topography. Strip cropping produces alternating
strips of different crops along natural contours. Terracing
reduces soil erosion on steep slopes. A shelterbelt is a row of
trees planted as a windbreak to reduce soil erosion.
Summary
1
Plate Tectonics and the Rock Cycle 298- The lithosphere, Earth’s outermost rigid rock layer, is
composed of plates that float on the asthenosphere, the
region of the mantle where rocks become hot and soft.
Plate tectonics is the study of the processes by which the
lithospheric plates move over the asthenosphere. Plate
boundaries are often sites of intense geologic activity:
earthquakes, volcanoes, and mountain building.
2. Rocks are aggregates
of one or more minerals.
The rock cycle shows
how rock slowly
cycles from one form
to another. The three
categories of rock are
igneous, metamorphic,
and sedimentary rock.
✓✓THE PLANNER
2 Economic Geology: Useful Minerals 302
- Minerals are metallic or nonmetallic elements or compounds
of elements that occur naturally in Earth’s crust. Highly
developed nations consume a disproportionate share of
the world’s minerals, but as developing countries become
industrialized, their needs for minerals increase. - Minerals are extracted through surface or subsurface mining.
Surface mining removes the overburden: the overlying
soil, subsoil, and rock strata. Strip mining, a type of surface
mining, produces a spoil bank when the overburden from
a new trench is put into an excavated trench. Subsurface
mining extracts resources from deep underground deposits. - Processing minerals often involves smelting, melting the ore
in a blast furnace to separate impurities from the metal.
3
Environmenal Implications
of Mineral Use 306- Surface mining destroys vegetation across large areas,
increasing erosion. Open-pit mining uses huge quantities of
water. Mining also affects water quality. Acid mine drainage
is pollution caused when dissolved toxic materials wash from
mines into nearby lakes and streams.
318 CHAPTER 12 Mineral and Soil Resources