The Amazing Adventure of Sea‑floor Spreading

What Is Sea‑floor Spreading?

Deep under the ocean, the Earth’s crust is not solid rock that never moves.
It is broken into huge tectonic plates that move over a hotter, weaker part of the Mantle. The mantle is mostly solid rock, but it can deform very slowly.
At mid-ocean ridges, hot material rises and cools into new crust while the plates move apart, so the ocean floor spreads.

How It Works

1. Magma Rises – Hot, melted rock (magma) climbs up through cracks in the crust.
2. New Rock Forms – When the magma touches the cold ocean water, it solidifies into new rock.
3. The Plates Move – New crust forms as the plates move apart, and older crust lies farther from the ridge.

The Atlantic widens by a few centimeters in many places each year, but the rate varies along the ridge.

The biggest crack is the Mid‑ocean Ridge. It is a long underwater mountain chain that circles the globe. The longest part is the Mid‑atlantic Ridge, which runs right through the middle of the Atlantic Ocean.

Why It Matters

• Creates New Ocean Floor – Every few million years, the sea floor gets fresh rock.
• Moves Continents – As the ocean floor spreads, the continents on top of the plates drift slowly.
• Makes Earthquakes And Volcanoes – The moving plates sometimes get stuck, and when they finally slip, they cause earthquakes. The magma that rises can also form underwater volcanoes.

Quick Quiz

1. What Is The Thick Layer Of Mostly Solid Rock Beneath Earth’s Crust Called?
   a) Crust b) Mantle c) Core d) Atmosphere

2. Which Underwater Mountain Chain Is The Longest Mid‑ocean Ridge?
   a) East Pacific Rise b) Mid‑Atlantic Ridge c) Southwest Indian Ridge d) Mariana Trench

3. How Fast Does The Atlantic Ocean Spread Each Year?
   a) 2–5 meters b) 2–5 centimeters c) 20–50 centimeters d) 0.2–0.5 centimeters

Great job! You now know how the ocean floor is always on the move. 🌍✨.