Erosion
What powerful force is constantly changing the shape of the Earth, transforming tall mountains into flat plains and carving deep canyons out of solid rock?
The Relentless Force of Nature
It is erosion! Every single day, water, ice, wind, and chemicals are slowly breaking down rocks, flattening hills, widening valleys, and deepening canyons all over the world.
Never! As Bill Nye the Science Guy explains, the process of erosion continues relentlessly. It happens day after day, year after year, for millions of years. The landscape you see today will never look exactly the same again.
Put Your Instincts to the Test
Think about what you already know about nature and the elements. Pick an answer for each question, then see if your instincts were right.
It washes away! The water slowly dissolves the solid material and carries it off downstream. Bill Nye the Science Guy demonstrates this by running a hose over a block of mineral salt, showing how liquid water can change the shape of solid objects over time.
Bare dirt with no plants! Plant roots act like natural nets holding the soil in place. Bill Nye the Science Guy shows this using a coin on top of wet sand. When water falls, the sand washes away everywhere except directly underneath the protective coin.
It expands and gets larger! This expansion is incredibly powerful. In the episode, Bill Nye the Science Guy fills a heavy glass bottle with water and freezes it using liquid nitrogen. The expanding ice easily splits the solid bottle right open.
Understanding the Science
Tap each card to reveal the core concepts behind how the Earth changes over time.
Key Concepts
The Process of Erosion
Tap to learn moreErosion is the slow, continuous wearing away of the Earth's surface. Bill Nye the Science Guy explains that every mountain, hill, and valley is constantly being shaped by natural forces. Even though rocks seem perfectly solid and unbreakable, they are actually breaking down bit by bit every single day. This process never stops, and it is responsible for creating many of the dramatic landscapes we see around the globe.
Water Erosion
Tap to learn moreFlowing liquid is one of the most powerful sculpting tools on our planet. When it rains, the water that falls erodes the earth by carrying loose soil away. In rivers and streams, the moving water picks up tiny grains of sand from the stream bed and carries them along. This sandy water acts just like a giant scouring pad. Over thousands of years, the friction wears its way deep into solid stone to carve massive canyons.
Ice Wedging
Tap to learn moreWhen the sun melts snow during the day, liquid water flows downward and fills the tiny cracks inside rocks. At night, when temperatures drop below zero, that water freezes and turns into solid ice. Ice takes up more space than liquid water, meaning it expands. This expansion acts like a wedge, forcing the rock apart and causing it to crack. Bill Nye the Science Guy demonstrates this by freezing a ball of wet modelling clay overnight until it splits open.
Wind and Sand
Tap to learn moreAs strong wind blows across dry landscapes like high deserts, it picks up sharp grains of quartz sand. The wind blasts this sand against solid rock formations. Every single particle of sand carries away a tiny bit of the mountain. Because the wind can only lift heavy sand particles a short distance off the ground, it usually erodes the base of rocks faster than the top, creating uniquely shaped formations known as mushroom rocks.
Wave Action
Tap to learn moreOcean waves are incredibly heavy and relentless. They constantly pound against coastal shorelines, bending the rock until it cracks. Eventually, pieces of the rock cliffs fall away, sometimes leaving isolated pillars standing in the water called sea stacks. The constant churning of the waves also rubs broken pebbles against one another for thousands of years, gradually grinding them down into the fine grains of sand that make up our beaches.
Chemical Erosion
Tap to learn morePhysical forces are not the only things breaking down rocks. Chemical erosion occurs when elements in the environment react with the minerals inside stones. For example, rainwater and oxygen combine to react with the iron trapped in rocks, turning it into iron oxide, or rust. This process leaves dark red streaks on the landscape and physically weakens the stone. This same process is what turned the copper on the Statue of Liberty bright green.
The Role of Living Things
Tap to learn moreLiving organisms play a complicated dual role in the shaping of the environment. On one hand, a tree can slow erosion down because its complex root system holds back loose soil and rocks during heavy rain. On the other hand, a tree can also speed erosion up. As strong tree roots grow deeper, they can physically wedge solid rock apart. Additionally, simple plants like lichen actively feed on chemicals inside rocks, breaking them down into soil.
Deep Time
Tap to learn moreBecause the Earth is so massive, these changes are incredibly difficult for humans to notice. Bill Nye the Science Guy points out that a canyon wall might only erode about half a centimetre every single year. However, if you multiply that tiny amount over a million or even fifteen million years, the cumulative effect is staggering. Understanding erosion requires scientists to think in terms of deep time, appreciating that slow, tiny changes add up to monumental transformations.
Try It: Freeze-Thaw Mountain Lab
Adjust the temperature slider below to simulate the changing of seasons. Watch what happens when water gets inside the mountain cracks and experiences multiple freeze-thaw cycles.
Apply Your Knowledge
Now that you understand how different natural forces break down our planet, it is time to match the elements to the specific erosion processes they cause.
Match the Concepts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are a city planner tasked with approving a brand new neighbourhood. A construction company wants to build several large, expensive houses on the side of a very steep, sandy hill with beautiful ocean views. Based on what you have learned about erosion and plant root systems, what advice would you give them to stop the houses from sliding down the hill during a heavy rainstorm?
What Has Changed Since This Episode Aired
This episode first aired in the 1990s. While the core science remains highly accurate, our modern understanding of how the Earth changes has expanded dramatically. Here are a few things scientists have discovered since then.
Updated: Yes, it is accelerating rapidly in certain areas. We have recently observed that a warming global climate is drastically accelerating erosion on Arctic coasts. As protective sea ice disappears earlier in the year, stronger ocean waves are free to crash directly into thawing permafrost cliffs, eroding them away at alarming rates—sometimes up to 20 metres in a single year!
Updated: Yes, we now know that microscopic life plays a huge role! The field of geomicrobiology has expanded massively since the 1990s. We now understand that billions of microscopic bacteria and fungi play a vital role in breaking down solid rock. They secrete specific organic acids, effectively "eating" the rock to extract vital minerals for survival.
Updated: Today, geologists use advanced lasers! Scientists now use LiDAR (Light Detection and Ranging) laser systems attached to drones and low-orbit satellites. This incredible technology allows us to map entire landscapes in 3D and measure erosion rates down to the exact centimetre, giving us a perfect picture of how landscapes change over time.
Test Your Understanding
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Results
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Reflection
Look around your own neighbourhood or a local park. Can you spot any signs of erosion at work? Think about a crack in the pavement with a weed growing out of it, or a patch of bare dirt where rainwater always washes down the street.
Episode Discussion
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