Today’s Wonder of the Day was inspired by Ms. Noble's Grade 3 Class from Barrie. Ms. Noble's Grade 3 Class Wonders, “How are rocks made” Thanks for WONDERing with us, Ms. Noble's Grade 3 Class!

Do you like to know how things are made? For example, when you order a grilled cheese sandwich, do you like to know what kind of bread and cheese are going to be used? If you don't want a Swiss cheese on rye sandwich, then you probably have an interest in how your sandwich is constructed.

But what about the bread and the cheese? Are you curious about how those products are made? Sometimes it's easy to see how things come to be the way they are. For bread, it's easy to follow a recipe that shows how ground grains are combined with other ingredients to produce the bread that comes hot and fresh out of the oven.

For other things, though, it's not nearly as easy to figure out how they're made. Take rocks, for example. Can you look at a rock and determine how it came to be? Unless you're a geologist, the answer is probably "no." So how are those hard lumps of mineral matter made?

That's a bit of a trick question, though, because there are three main types of rocks: igneous, sedimentary, and metamorphic. And, of course, each type forms differently. Let's take a look at each type of rock and how it comes to be.

Igneous rocks form when melted rock cools into a solid. This can happen underground, where liquid rock is found in the form of magma, or above the ground, where lava is released during a volcanic eruption. Common examples of igneous rocks include granite, basalt, pumice, and obsidian.

While igneous rocks can form in a matter of minutes as lava erupts and cools quickly on Earth's surface, sedimentary rocks can take millions of years to form. When soil and surface materials erode over time, they leave layers of sediments.

Over long periods of time, layer upon layer of sediments form, putting intense pressure on the oldest layers. Under great pressure and heat, lower layers of sediments eventually turn into rocks. Common examples of sedimentary rocks include sandstone, limestone, and shale.

Metamorphic rocks are the products of rocks that have undergone changes. If you're familiar with the term metamorphosis as it describes the change a caterpillar goes through to become a butterfly, then you'll understand that the term also applies to rocks that change in form.

Metamorphic rocks may have started out as igneous, sedimentary, or even another type of metamorphic rock. Changes in these rocks are spurred either by collisions that occur at the boundaries of colliding tectonic plates or intense heat and pressure underground. Common types of metamorphic rocks include marble, soapstone, slate, and gneiss.

Although they might seem rather permanent, rocks actually change over the course of millions of years as part of what scientists call the rock cycle. For example, a volcano erupts, spewing lava that turns into igneous rock.

Over time, weather erodes that igneous rock, turning it into small pieces of sediment. In turn, those pieces of sediment become layers of compacted sediment that turn into sedimentary rock over the course of millions of years.

Over millions of more years, that sedimentary rock gets buried under other rocks and ends up deep underground. Heat and pressure deep in the Earth's crust turn the sedimentary rock into metamorphic rock, and the cycle can start all over again! Of course, rocks don't have to follow this exact progression. There's a nearly endless variety of ways rocks can turn from one type into another in a never-ending cycle.

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