Warm-UpWarm-Up

How would you describe the difference between a new tombstone and one that is

100 years old?

Rocks & WeatheringRocks & Weathering

The Effects ofThe Effects of Weathering Weathering

• Weathering is the process that breaks down rocks and other substances at Earth’s surface

Sierra Nevada Mtns. ~20 myo Appalachian Mtns. ~250 myo

TwoTwo Types of Weathering Types of Weathering

• Mechanical (physical)

• Chemical

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)

– rock is physically broken into smaller pieces without changing what the rock is composed of

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)– rock is physically broken into smaller pieces without changing

what the rock is made of

Examples:• Abrasion—grinding

away of rock by other

rock particles carried

by water, ice, wind,

or gravity

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)– rock is physically broken into smaller

pieces without changing what the rock

is made of

Examples:• Ice wedging—water freezes

and expands, acting like a

wedge that pushes open

cracks in rocks

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)– rock is physically broken into smaller pieces without changing

what the rock is made of

Examples:• Exfoliation—layers

of rock crack and

flake off when

pressure is removed

from the rock

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)– rock is physically broken into smaller pieces without changing

what the rock is made of

Examples:• Plant growth—roots

grow into cracks in

rocks and pry cracks

farther apart

Two Types of WeatheringTwo Types of Weathering

• Mechanical Weathering – (also called physical weathering)– rock is physically broken into smaller pieces without changing

what the rock is made of

Examples:• Animal action—animal

burrowing breaks apart

rocks in the soil

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals

– rock is broken down by chemically changing the minerals that makes up the rock into new minerals

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals– rock is broken down by chemically changing the minerals that

makes up the rock into new minerals

Examples:• Water—water

dissolves minerals

in some rocks

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals– rock is broken down by chemically changing the minerals that

makes up the rock into new minerals

Examples:• Oxidation—oxygen

reacts with minerals

(iron) in some rocks

(“rusting”)

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals– rock is broken down by chemically

changing the minerals that makes up the rock into new minerals

Examples:• Carbonic acid—carbon

dioxide and water form carbonic acid which reacts with minerals (marble & limestone) in some rocks

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals– rock is broken down by chemically changing the minerals that

makes up the rock into new minerals

Examples:• Living organisms—

plant roots & lichens (plant-like organisms) produce weak acids that can dissolve some minerals in rocks

Two Types of WeatheringTwo Types of Weathering

• Chemical Weathering – rocks are made of minerals– rock is broken down by chemically changing the minerals that

makes up the rock into new minerals

Examples:• Acid Rain—burning

fossil fuels releases chemicals into the air that react with water to form acids which can dissolve rocks

Rate of WeatheringRate of Weathering

• How fast rocks are broken down depends on:

-Type of rock

-Climate

Rate of WeatheringRate of Weathering

• How fast rocks are broken down depends on:

-Type of rock• some rocks are made

of minerals that

dissolve easier

Example:

limestone contains calcium

that dissolves easily

Rate of WeatheringRate of Weathering

• How fast rocks are broken down depends on:

-Type of rock• some types of rock

are permeable (they contain tiny holes that absorb water), so they weather faster

Example: marble is more permeable than slate

Marble 1897Slate 1856

Rate of WeatheringRate of Weathering

• How fast rocks are broken down depends on:

-Climate• Mechanical & chemical

weathering occur faster in places that are wet (have more rain)

Example: pyramids in Egypt have weathered slowly because of dryness of desert

Egypt ~4500 yo

Mexico ~1800 yo

Rate of WeatheringRate of Weathering

• How fast rocks are broken down depends on:

-Climate• chemical weathering occurs

faster in places that are hot

Example: granite weathers ten times faster in hot climates than cold

Mojave Desert

Connecticut