WEATHERING You need your spiral. We will be meeting in the Library tomorrow.

WEATHERINGYou need your spiral. We will be meeting in the Library tomorrow.

Why do we care about rocks…?

We can always take pointers from earth on how to be sustainable.

Rocks make soil

Why is soil important?Organisms, mainly microorganisms, inhabit the soil & depend on it for shelter, food & water.

Plants anchor themselves into the soil, and get their nutrients and water. Terrestrial plants could not survive without soil, therefore, humans could not exist without soil either.

Parent MaterialThe rock that has slowly broken down into smaller particles by biological, chemical, and physical weathering.

To form 2.5 cm (1 in.) it may take from 200-1000 years.

Soil Formation

Mechanical Weathering: no change in chemical composition--just disintegration into smaller pieces

Mechanical Weathering

Exfoliation:

Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands

(due to the lower confining pressure) resulting in exfoliation.

Sheet Joints(Exfoliation)

Stone Mountain, GA

Half Dome, Yosemite, CA

Exfoliated Domes, Yosemite

Stone Mountain, GA

Stone Mountain, Georgia, showing the product of exfoliation due to unloading

Frost Wedging: rock breakdown caused by expansion of ice in cracks and joints

Shattered rocks are common in cold and alpine environments where repeated freeze-thaw

cycles gradually pry rocks apart.

WeatheringThermal expansion due to the extreme range of temperatures can

shatter rocks in desert environments.

Repeated swelling and shrinking of minerals with different expansion

rates will also shatter rocks.

Agents

Water

Wind

Geological processes

Role of Physical Weathering

1) Reduces rock material to smaller fragments that are easier to transport

2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering

Surface Area and Weathering

Chemical Weathering

A plant’s roots or animal cells undergo cell respiration and the CO2 produced diffuses into soil, reacts with H2O & forms carbonic acid (H2CO3). This eats parts of the rock away. CHANGES THE COMPOSITION

Olivine/pyroxene to clay

+ H2CO3 (acid)

Feldspars to clay

+ H2CO3 (acid)

Quartz to quartz (!)

+ anything

This photo of Lime Sink was taken on 20 July 1932, over a week after the drawdown, which occurred over the night of 9-10 July.

‘Karst’ landforms develop in areas underlain with limestone

Five main factors that affect the rate of weathering.

Climate: Soil forms faster in warm, wet climates, because heat and moisture speed most physical, chemical and biological processes.

Organisms: Plants and decomposers add organic matter to soil over time

Topography: Hills and valleys affect exposure to sun, wind and water and they influence how soil moves (erosion)

Parent materials: Its attributes influence properties of the resulting soil.

Time: soil formation can take decades, centuries or millennia.