Third Grade Earth Science
Studying the earth can be really useful. This is because when we study the earth, we come across patterns or cycles. These patterns help us understand what has happened to the earth, its present state, and what may happen to it in the near or distant future. Think of it like a puzzle. You won't be able to fit all the pieces together unless you have all the details. It can take a lot of observation of the earth or the same patterns over and over before we realize what all the details are or what it is we are looking at. As you read about and do the following experiments, remember that earth science is a science that requires a lot of patience.
Rocks and Minerals
A good part of the earth is made up of rocks and minerals. We see them all around as little bits of rock, we see giant boulders here and there, and we also see big mountains made of rock. While they may all just look like rocks to you, they are actually very different. Every rock has a story to tell, and every rock is still within its own story called the rock cycle.
To understand the rock cycle, we must first look at what rocks are made of. Rocks are mostly made of minerals, crystals, little bits of rock, bits of sand, and fossils. We can see what a rock is made of by studying what it looks like on the outside and on the inside. Through studying and comparing the different materials that make up rocks, scientists have been able to classify rocks into three different categories.
The first category is igneous. These rocks are formed when magma (hot, molten rock; also known as lava) that is boiling and bubbling deep within the earth cools and solidifies. There are two types of igneous rock because there are two ways that the magma can cool. Extrusive igneous rocks are formed when the magma is pushed towards the surface of the earth. This happens when volcanoes erupt or when the magma pushes up from underground. The magma cools very quickly when it's on the surface of the earth because the temperature on the surface is much cooler than the temperature below. This rapid cooling forms extrusive igneous rocks which are characterized by a very fine or glass like texture.
Intrusive igneous rocks, on the other hand, are formed when the magma cools while still inside the earth. Even though the temperature below is hot enough to boil and melt rock, as the magma moves along, it slowly cools over time (thousands of years.) The effect of this slow cooling is that the minerals in the earth stick to the rock and grow, making space for themselves within the rock face. As a result, intrusive igneous rocks are characterized by a very grainy or coarse texture.
Second on the list of rock categories is sedimentary. This type of rock is formed out of other rocks, bits of sand, and fossils. These materials are compacted together deep within the earth. Through constant pressing together, the materials stick towards each other and form a rock. We call it sedimentary because it's made out of different bits and parts, or sediments!
There are three types of sedimentary rock. Their classification is based on the material that has been compacted together. The first type of sedimentary rock is biologic. This is sedimentary rock that is made up of once living things. For example, when animal shells or bits of dead animals from the sea become compressed or compacted together for millions of years, they can form limestone, a type of sedimentary rock. When plants are compacted for millions of years, they form coal, which is also a type of sedimentary rock.
Page Two: Different Categories of Rocks (Third Grade Earth Science continued)
