Warm-Up How would you describe the difference between a new tombstone and one that is 100 years old?

Rocks & Weathering

The Effects of Weathering Weathering is the process that breaks down rocks and other substances at Earth’s surface Sierra Nevada Mtns. ~20 myoAppalachian Mtns. ~250 myo

Two Types of Weathering Mechanical (physical) Chemical

Two 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 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 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 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 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 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 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 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 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 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 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 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 Weathering How fast rocks are broken down depends on: -Type of rock -Climate

Rate 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 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 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 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