Changes to the Earth’s surface
The changing Earth
• The surface of the Earth is always changing.
The Rock cycle
• The rock cycle shows how rocks change back and forth between sedimentary, igneous, and metamorphic rocks.
The rock cycle - Igneous• Igneous rocks form when
melted rock cools and solidifies.
• The crystal size in an igneous rock is determined by how fast the rock cooled.
• How fast the rock cooled is determined by how close to the surface the rock was, and how large the chamber was.
• Igneous rocks can be extrusive or intrusive
The rock cycle - Igneous
• Examples of igneous rocks include:– Obsidian– Granite– Basalt– Pumice– Rhyolite
The rock cycle – Sedimentary
• Sedimentary rocks are formed by weathering, erosion, deposition, compaction, and cementation of other rocks.
The rock cycle – Sedimentary
• Examples of sedimentary rocks include:– Sandstone– Limestone– Flint– Shale– Coal– Limestone
The rock cycle – metamorphic
• Metamorphic rocks form when heat and pressure deep beneath earth’s surface cause one type of rock to change into another type of rock.
The rock cycle – metamorphic
• Examples of metamorphic rocks include:– Gneiss (from Granite)– Quartzite (from
Sandstone)– Schist– Slate (from Shale)– Marble (from Limestone)
Energy in the rock cycle
• What types of energy are needed to form each type of rock?– Igneous– metamorphic– Sedimentary
Rock cycle
• Heat energy is important in the formation of igneous and metamorphic rocks.
• Where does that heat come from?
Heat energy
• The earth gets hotter the deeper down you go, but why?– Radioactive decay
Kinetic energy
• Some of the heat energy in the mantle is transformed into kinetic energy in the form of convection currents that form in the mantle.
Kinetic energy
• Convection currents move the plates of the crust back and forth.
• A place where 2 plates meet is called a fault.
Kinetic energy Potential energy
• Kinetic energy of the moving plates can be converted into potential energy when two plates collide and “stick” together.
• The potential energy builds up until it is finally converted back into kinetic energy and the plates “slip”
Plate boundaries
• Plates that pull apart are called divergent plates
• Plates that push together are called convergent plates
• Plates that slide past each other are called transform plates.
• What do you think would happen to the earth at each type of boundary?
Plate movement
• As plates slide over, under, or past each other, they change the surface of the earth.
Plate movement
• Plates that push together can cause the earth to “crumple” and form mountains.
Plate movement
• When continental and oceanic plates collide, they can produce volcanoes.
Plate movement
• When plates “slip”, “smash” or “pull” apart they produce earthquakes.
• During an earthquake, potential energy is converted to kinetic energy.
• (Remember that this mechanical energy started as heat energy inside the earth.)
Plate movement• Some of the heat energy
from the earth reaches the surface (as in a volcano.)
• Some heat energy is transformed into mechanical energy in the form of convection currents, moving plates, earthquake waves, flowing lava, etc…
Energy to infinity and beyond!
• Earthquakes, volcanoes, and mountain formation all occur when the heat energy from inside the earth makes its way to the surface. (Either as heat energy or mechanical energy.)
Energy to infinity and beyond!
• Earthquakes and volcanoes can change earths surface very rapidly.
• Mountains building is a slow and gradual process that changes earths surface.
• These changes all occur because energy from earths interior transfers to the earth’s surface.
Changes to Earth’s surface
• Some changes to the Earth’s surface are not caused by energy from the interior of the earth.
• These changes can come from weathering, erosion, deposition, gravity, glaciers, and other “agents” of change.
Weathering
• Weathering occurs when rock on the surface of the earth breaks down into smaller pieces.
• Weathering can be mechanical or chemical.
Mechanical Weathering
• Mechanical weathering is when mechanical energy creates weathering. This mechanical energy could come from:– Moving water/wind
(abrasion)– Freezing ice– Burrowing animals– Growing plant roots
Chemical weathering• Chemical weathering occurs
when chemical energy causes weathering to occur.
• Things that could cause chemical weathering include:– Acid rain– Oxygen (oxidation)– Living things making acids to
break down rock. (like lichens)
Erosion and deposition
• Erosion occurs when water, wind, or ice move weathered rock particles from one place to another.
• Deposition is when those particles being carried by erosion get laid down somewhere.
Weathering, erosion, and deposition
• Weathering, erosion, and deposition are important parts in the process of soil formation.
Gravity
• Gravity changes the surface of the earth. Particles that weather and erode in the mountains get carried to the valleys.
• Gravity moves particles and sediment downhill.
Gravity
• Gravity can cause several types of “mass movement” downhill including:– Landslide– Mudflow– Slump– Creep
Gravity – Mass movement
• Landslides occur when rock and soil move quickly down a slope
• Mudflows occur when water, rock, and soil move downhill. (Usually during heavy rain.)
Gravity – Mass movement
• Slumps occur when an entire section of a hillside suddenly slides down a slope but stays together.
• Creeps occur when rock and soil moves downhill very slowly.
Glaciers• Glaciers move slowly
across the land. As they move, they shape the land in many ways.
Glaciers
• Glaciers create features in the earth such as:– U-shaped valleys– Cirques– Horns– Drumlins
Weathering Erosion and Deposition
• Weathering, erosion deposition and gravity can change the surface of the earth gradually or rapidly.
Rapid change
• Flash floods, landslides, mudflows, earthquakes, volcanoes can all change the earth rapidly.
Gradual change
• Mountain formation, mountain destruction, weathering, erosion, creep, and glacial activity are all gradual changes to earth’s surface.
Mountain building
• The average mountain that is actively being built is moving upward at a rate of 6 mm/year and being eroded downward at a rate of 1 mm/year.
• A mountain that takes 5 million years to build might take 100 million years to erode away.
Mountain building
• As a mountain erodes away, the roots of the mountain push upward.
• For every 5 mm of the mountain that erode away, the roots push up 4 mm.
• The taller the mountain, the faster erosion occurs.
