Download Dynamic Earth Chapter 5 Highlights Weathering and Soil Formation

Dynamic Earth
Chapter 5 Highlights
Weathering and Soil Formation
A. Highlights for Section 1 pages 113-119
 Slow and continuous breaking down of rocks and other materials on Earth’s
surface = weathering
o Rocks on Earth’s surface are broken down by 2 types of weathering:
 Mechanical weathering – forces break rock into smaller pieces
but do not change chemical make-up of rocks
 Chemical weather – chemical make-up of rocks changed
 Mechanical Weathering
o Rocks broken into different shapes and smaller pieces
 Temperature changes – cause particles on surface of rock to
crack or flake off
 Exfoliation – pieces of rock break off in curved sheets or slabs
parallel to rock’s surface
 Frost action – water seeps into cracks and freezes. It expands
and breaks rock.
 Gravity pulls loosened rocks into landslide = smaller pieces
made
 Wind blown sand causes abrasions---wearing away of rocks
 Running water may cause abrasions
 Chemical Weathering
o Changes occur in mineral composition or chemical make-up of rocks
 Water dissolves most of minerals that holds rock together
 Water can form acids that speed decomposition
 Oxidation = oxygen chemically combines with another substance
to produce an entirely new one
 Carbonation = carbonic acid may react with other substances in
rocks—dissolving them
 Rain = sulfur oxides dissolve in rain water to produce sulfuric
acid. This corrodes or wears away rocks.
 Plants = form acids that dissolve certain minerals in rocks
 Rate of weather depends on several factors
o Moisture
o Exposure on Earth’s surface
 Stable rock = minerals in rock resist chemical weathering
M. Highlights for Section 2 pages 120-122
 Soil is formed when rocks are continuously broken
down by weathering until they become small pieces
o Soil that remains on top of its parent rock--residual soil
o Soil that is moved away from its place of origin--transported soil
o Layer of rock beneath soil---bedrock
 Certain bacteria in soil cause the decay of dead
plants and animals into substances they are made of
o Decaying material---humus – very important for
growth of plants
R. Highlights for Section 3 pages 123-126
 Pieces of weathered rock and organic material or
humus are 2 main ingredients of soil
o Air and water fill spaces between soil particles =
pore spaces
 As soil forms, it develops separate soil layers called
horizons
o Each horizon is different
o Cross section of soil horizons called soil profile
 Soil that developed 3 horizons is called mature soil
o Uppermost layer of mature soil is called a
horizon---soil is called top soil
 Consists of humus and other organic
materials
 Humus supplies minerals for plant growth
 Most fertile part of soil
o Water that soaks into ground washes some
minerals from a horizon into 2nd layer of soil---B
Horizon
 Process called leaching
 Soil in B Horizon---subsoil
o Third layer of soil is called C Horizon
 Composition similar to parent rock