Introduction

Physical Weathering  Takes place over tens to hundreds of years  Processes that take place in the surface environment of the Earth  Causes solid rock to be broken down into loose pieces of minerals and rocks

Chemical Weathering  Rocks from deep in the Earth (are at higher temperature and pressure)  When these rocks are brought near the surface (different chemical environment). The change in conditions makes some of the minerals chemically unstable  Some minerals may breakdown chemically

 Physical weathering and chemical weathering act together. However, they will be studied separately.

Physical Weathering  Breaks rocks apart without changing their mineral composition

Ice Wedging  Water seeps into cracks in rocks  Temp. drops, water freezes & expands  The expansion puts enormous pressure on the surrounding rocks  Frozen water acts like a wedge, making cracks wider

 After repeated freezing and thawing, the rocks break apart.  Expansion and contraction of water also causes potholes in streets.

Plant Roots  Plants take root in cracks of rocks  Roots become larger and exert pressure  Cracks in rocks become larger and rocks break apart

Chemical Weathering  Minerals in the rock dissolve in water forming a weak acid (Acid Rain)  Acidic water makes some rocks dissolve even faster  Rocks made of the mineral calcite (for example, limestone, are most easily dissolved by acidic water  Without water, chemical reactions that weather rocks happen slowly

Biological Processes in Weathering  Lichens

Lichens (continued)  Among the first organisms that establish themselves on bare rocks  Produce a diluted acidic solution which break down the minerals in rocks slowly

Weathering of the mineral material in soil  Microorganisms are present in the soil in amazingly large numbers

 Larger animals, like earthworms and rodents also live in the soil

 As plants and animals die, they add organic material to the soil

 This organic material decays and is converted into carbon dioxide  Carbon dioxide forms more weak acid (carbonic acid) promoting more weathering

The Earth Systems and Weathering

Formation of karst landform

 Formed by chemical weathering  Carbon dioxide is produced naturally by animals, the use of fossil fuels and the decay of organic matter in soil  Some of this carbon dioxide is dissolved in surface waters forming an acid  In areas where pure limestone bedrock and lots of rainfall, karst topography often develops

 Happens both on rock surfaces and cracks and fractures in limestone, as acidic groundwater percolates downward

 Leads to large underground networks of caverns

 Sometimes whole blocks of homes will collapse, forming a sinkhole

Copy Chart The Atmosphere The Biosphere The Geosphere The Hydrosphere

 In boxes, write how karst topography occurs in each of the four Earth Systems