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Changing Earth
Surface

Explore how weathering, erosion, and deposition reshape our planet over time, and learn to use evidence to explain these powerful processes.

Earth & Space Science

What Is Earth's Surface?

Earth's surface is the outermost layer of our planet: the mountains, valleys, plains, coastlines, and ocean floors we see around us. This surface is not permanent: it is constantly being shaped and reshaped by natural forces.

Three Agents of Change

Weathering
The breaking down of rocks into smaller pieces by physical, chemical, or biological processes: without moving the pieces.
Erosion
The transport of weathered material by water, wind, ice, or gravity from one location to another.
Deposition
The dropping or settling of eroded material in a new location, building up landforms like deltas and sand dunes.

Why Does It Matter?

Understanding how Earth's surface changes helps us predict natural hazards (landslides, coastal erosion), protect communities, and manage natural resources like soil and water. Scientists use evidence from rock layers, fossils, and landforms to reconstruct Earth's history.

The Rock Cycle Connection

Igneous Rock Sedimentary Rock Metamorphic Rock Sediment Weathering & Erosion Compaction & Cementation Heat & Pressure Melting & Cooling Heat & Pressure

Constructive vs. Destructive Forces

Constructive Destructive
Definition Build up or add material to Earth's surface Break down or remove material from Earth's surface
Examples Volcanic eruptions, deposition, mountain building Weathering, erosion, landslides
Result New landforms: mountains, islands, deltas Worn-down landforms: canyons, valleys, cliffs
Speed Can be fast (eruption) or slow (sediment buildup) Can be fast (earthquake) or slow (river erosion)

Types of Weathering

Physical
Rock breaks into smaller pieces without changing its chemical makeup. Caused by ice wedging, temperature changes, plant roots, and abrasion.
Chemical
Rock's chemical composition changes, forming new minerals or dissolving. Caused by acid rain, oxidation (rust), and reactions with water.
Biological
Living organisms break down rock. Tree roots crack stone, lichens produce acids, and burrowing animals loosen soil.

Four Agents of Erosion

Erosion Transport Water Rivers, waves, rain runoff Wind Deserts, coastlines Ice (Glaciers) Carves valleys, moves boulders Gravity Landslides, rockfalls

Deposition: Where Sediment Settles

Source Delta Sediment carried by current Fast current Slow current

Slow vs. Rapid Changes

Slow Changes Rapid Changes
Timescale Thousands to millions of years Seconds to days
Examples Weathering, soil formation, canyon carving Earthquakes, volcanic eruptions, landslides
Visible? Not within a human lifetime (usually) Dramatic and immediately visible
Evidence Rock layers, fossils, worn landforms Rubble, ash layers, shifted ground

How to Use Evidence

1
Observe the landform. Describe exactly what you see: shape, size, material, location.
2
Identify the process. Determine which force (weathering, erosion, or deposition) could produce that feature.
3
Connect evidence to process. Explain how the evidence (rock layers, shape, sediment type) matches the process.
4
Consider the timescale. Was this a slow change (millions of years) or a rapid event (days)?
5
Write a claim with reasoning. State your conclusion and cite specific evidence to support it.

Example: The Grand Canyon

Youngest Limestone Sandstone Oldest Colorado River ~1.8 km deep

Example: Volcanic Island Formation

Sea Level Ocean Floor Magma Eruption New Island Constructive Force

Example: Glacial Valley Shape

V-Shaped Valley Carved by a river U-Shaped Valley Carved by a glacier Wide, flat floor Narrow point vs.

Evidence from Rock Layers

1
Superposition: In undisturbed layers, the oldest rocks are on the bottom and the youngest are on top.
2
Fossils: Different organisms in different layers tell us about past environments and how conditions changed.
3
Unconformities: A gap in rock layers shows a period where erosion removed material before new layers were deposited.
4
Cross-cutting: A feature (like a fault or intrusion) that cuts across layers is younger than the layers it cuts through.

Common Mistakes

✕ Confusing Weathering and Erosion
Weathering breaks rock apart in place. Erosion moves the broken pieces. They are related but different processes.
✕ Ignoring Slow Changes
Students often focus only on dramatic events. Most of Earth's surface was shaped by slow, gradual processes over millions of years.
✕ Claiming Without Evidence
Saying "erosion caused this" is not enough. You must cite specific evidence (rock type, shape, layers, fossils) to support your claim.

Question 1 of 5

A scientist finds a deep canyon with exposed rock layers and a river at the bottom. Which process most likely formed this canyon?

Question 2 of 5

Which of the following is an example of a constructive force?

Question 3 of 5

A geologist observes a wide, U-shaped valley with steep walls and a flat floor. What evidence does this shape provide about the valley's formation?

Question 4 of 5

A student says: "Weathering and erosion are the same thing." What is the best correction?

Question 5 of 5

A river deposits large amounts of sediment at its mouth, forming a fan-shaped landform. What is this landform called, and what process created it?