Earth's Surface Changes
Discover how weathering, erosion, and powerful forces shape and reshape the Earth's surface over time.
Weathering and Erosion
The Earth's surface is always changing. Rocks that seem permanent are actually being slowly broken down and moved. Two key processes are responsible: weathering and erosion.
Weathering
The breaking down of rocks where they are (they stay in place).
- 1.Physical weathering: Water gets into cracks and freezes, expanding and splitting the rock.
- 2.Chemical weathering: Rainwater (slightly acidic) slowly dissolves rock over thousands of years.
- 3.Biological weathering: Plant roots grow into cracks and push rocks apart.
Erosion
The moving of broken rock and soil from one place to another.
- 1.Water erosion: Rivers and rain carry rock and soil downhill.
- 2.Wind erosion: Wind blows sand and small particles to new places.
- 3.Ice erosion: Glaciers (huge rivers of ice) carve out valleys as they move.
Inquiry Question: Look around your local area. Can you see any signs of weathering or erosion? Think about cracked footpaths, worn-down steps, or gullies in the soil after rain.
Types of Rocks
There are three main types of rocks, and they are all formed in different ways. Rocks are constantly being recycled in the rock cycle.
Igneous
Formed when hot, melted rock (magma or lava) cools and hardens.
Examples: Granite, basalt, obsidian
"Fire rock" (ignis = fire)
Sedimentary
Formed from layers of sediment (sand, mud, shells) pressed together over millions of years.
Examples: Sandstone, limestone, shale
Often contains fossils!
Metamorphic
Formed when existing rocks are changed by extreme heat and pressure deep underground.
Examples: Marble, slate, quartzite
"Changed rock" (meta = change)
Fossils
Fossils are the preserved remains or traces of plants and animals that lived millions of years ago. They are most commonly found in sedimentary rock.
When an animal dies, it can be buried by layers of sediment. Over a very long time, the sediment hardens into rock and the remains are preserved as a fossil. Fossils help scientists learn about life in the past.
Natural Disasters that Change Earth's Surface
Some changes to Earth's surface happen suddenly and powerfully. These natural events can reshape the landscape in hours or even minutes.
Earthquakes
The Earth's outer layer (crust) is made of huge pieces called tectonic plates. When these plates move and bump into each other, the ground shakes.
Effects: Cracking of the ground, landslides, and damage to buildings.
Volcanoes
A volcano is an opening in the Earth's crust where hot, melted rock (magma) pushes up from deep underground. When it reaches the surface, it is called lava.
Effects: New rock and land is formed when lava cools. Ash can cover large areas.
Floods
Heavy rain or melting ice can cause rivers to overflow. Water carries soil and rock, reshaping the land.
Effects: Erosion of river banks, new sediment deposits, changed landscapes.
Landslides
When soil and rock on a hillside become unstable (often from rain or earthquakes), they can slide downhill rapidly.
Effects: Dramatic reshaping of hillsides and valleys.
Key Vocabulary
Weathering
The breaking down of rocks in place by water, wind, ice, or living things.
Erosion
The movement of broken rock and soil from one place to another by water, wind, or ice.
Fossil
The preserved remains or trace of an ancient living thing, found in rock.
Sediment
Small pieces of rock, sand, mud, or shells that settle in layers.
Magma / Lava
Hot, melted rock. Called magma underground and lava when it reaches the surface.
Tectonic Plates
Huge pieces of Earth's crust that move very slowly, causing earthquakes and volcanoes.
Worked Examples
A sandstone cliff near the beach is getting smaller each year. Is this weathering or erosion?
Step 1: The waves crash against the cliff, breaking off small pieces (weathering).
Step 2: The water carries the broken pieces away (erosion).
Answer: It is both. Weathering breaks the rock down, and erosion carries the pieces away. They work together.
A scientist finds a fossil of a fish on top of a mountain. How did it get there?
Step 1: The fish must have died in water and been covered by sediment (forming sedimentary rock).
Step 2: Over millions of years, tectonic plates pushed the rock upward, forming a mountain.
Answer: The land was once under the sea. Slow movement of tectonic plates pushed the seabed upward over millions of years.
What type of rock is formed when lava from a volcano cools down?
Step 1: Lava is melted rock that has come to the surface.
Step 2: When melted rock cools, it hardens into solid rock.
Answer: Igneous rock is formed when magma or lava cools and hardens. The word "igneous" comes from the Latin word for fire.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Which type of rock is most likely to contain fossils?
Question 2
What is the difference between weathering and erosion?
Question 3
Granite is formed when magma cools slowly underground. What type of rock is granite?
Question 4
What causes earthquakes?
Question 5
Tree roots growing into a crack in a rock is an example of:
Key Concepts Summary
- ●Weathering breaks rocks down in place; erosion moves the pieces to new locations.
- ●The three rock types are igneous (from cooled magma), sedimentary (from compressed layers), and metamorphic (changed by heat and pressure).
- ●Fossils are preserved remains of ancient life, mostly found in sedimentary rock.
- ●Earthquakes are caused by moving tectonic plates; volcanoes release magma from inside the Earth.
- ●Earth's surface is constantly changing, both slowly (erosion) and suddenly (earthquakes, eruptions).