#rockcycle #earthscience #ngscience @NGScience In science, there are lots of cycles. Put simply, a cycle is a pattern that repeats over and over. For example, the Earth rotates on its axis in a regular cycle, giving us day and night. It also revolves around the Sun in a yearly cycle, which creates the seasons.
Matter moves in cycles too—like water changing from solid to liquid to gas and back again.
There are life cycles as well: a frog lays eggs, which hatch into tadpoles, grow into froglets, and eventually become adult frogs, ready to start the cycle again.
But there's another repeating pattern on Earth—something we often don’t think of as moving in cycles. It’s a slow, powerful process that shapes mountains, builds up new land, and breaks down the Earth's surface bit by bit. Unlike the fast-paced cycles of weather or life, this one unfolds over thousands—or even millions—of years.
It’s called the rock cycle.
All of the rock on Earth goes through a natural cycle too.
But unlike the quick changes we see in weather or life cycles, the rock cycle moves much, much slower. Let’s take a look...
There are three main types of rock that are all connected in a never-ending cycle: igneous rock, sedimentary rock, and metamorphic rock. Each type forms in a different way, but over time, one type can change into another.
Igneous rock forms when melted rock cools and hardens. This melted rock is called magma when it's deep underground, and lava when it reaches the Earth's surface during a volcanic eruption. When magma cools slowly beneath the surface, it forms rocks like granite. When lava cools quickly after a volcano erupts, it forms rocks like basalt.
Over time, the layers are pressed together, in a process called cementation. This process forms sedimentary rocks like sandstone and limestone.
If sedimentary or igneous rocks are buried deep underground, heat and pressure can cause them to change, creating metamorphic rocks. For example, limestone can turn into marble, and shale can become slate.
If metamorphic rocks are pushed even deeper, they may melt into magma again. And when that magma cools, it forms new igneous rocks, and the cycle continues.
The rock cycle takes a long time—thousands to millions of years—but it’s always happening. Rocks are constantly being formed, broken down, changed, and formed again in a repeating natural process.
Just like the cycles we see in the movement of the Earth, the states of matter, and life cycles, the rock cycle is another way Earth keeps things moving and changing. And even though it takes much longer, it’s still part of the endless pattern of cycles that shape our planet.
Quiz: The Rock Cycle
1. True or False. The rock cycle is a fast-moving process, similar to weather cycles.
Answer: False
2. Which of the following rocks forms when magma cools slowly beneath Earth’s surface?
A) Basalt
B) Sandstone
C) Granite
D) Slate
Answer: C) Granite
3. ________ rocks are formed when layers of sediment are pressed and cemented together.
Answer: Sedimentary
4. What causes metamorphic rocks to form from sedimentary or igneous rocks?
Answer: Heat and pressure deep underground cause the rocks to change into metamorphic rocks.
5. Which type of rock is formed from lava that cools quickly after a volcanic eruption?
A) Marble
B) Basalt
C) Shale
D) Granite
Answer: B) Basalt
6. When magma reaches Earth’s surface, it is called ________.
Answer: lava
7. True or False. Metamorphic rock can melt back into magma, continuing the rock cycle.
Answer: True
8. List the three main types of rocks in the rock cycle.
Answer: Igneous, sedimentary, and metamorphic
9. Name a metamorphic rock and describe how it forms.
Answer: Examples: Marble forms when limestone is exposed to heat and pressure deep underground. Slate forms when shale is subjected to heat and pressure over time.
10. The process of layers of sediment being pressed together to form sedimentary rock is called ________.
Answer: cementation
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