Sedimentary rock is a form of rock that is made when tiny particles of rocks and minerals are pushed and pressed together to form one rock. Sedimentary rock is usually made by water, wind, and erosion.
Erosion is the breaking down of mountains and other rock formations by strong winds and ice melting at the tops of mountains; sending water flowing over the rocks below. The erosion wears the surface off the rocks; breaking them into tiny pieces scientists call sediment.
The sediment comes together at the bottom of a mountain or on the floor of a river, lake or stream and is forced or packed together.
It takes time
It takes time for sedimentary rocks to form. And unlike other non-living things, sedimentary rocks can ‘grow’ as more sediment is forced onto an existing sedimentary rock. This is why:
- Sedimentary rock often looks like it has many different layers. In fact, it does!
- Sedimentary rocks often have fossils.
Fossils are shapes of plants or animals left in a rock after the plant or animal dies and rots away. The reason sedimentary rocks have fossils is that leaves and bugs and other plants and animals can get trapped in between the layers of sedimentary rock as new layers are formed. There is enough air and water flowing through the sediment as it forms into a rock to rot the plant or animal; leaving only the impression of it.
Make your own rocks and fossils
Okay, so it won’t actually be a rock, but…
Here is what you need:
- Three or more colors of clay or craft dough
- Small shell
- Chocolate chips, peanut butter chips, white chocolate chips, chopped nuts
- Clear glass measuring cup
- 4 or 5 Hardback books
- Butter knife
- Small dish
Here is what you do
- Place a piece of clay on a flat surface and press the coin or shell into the clay to make an impression, but be careful to not press it completely thru the clay
- Remove the shell, coin, or another item
- Repeat the process with each piece of clay
- Set the clay in a sunny location and leave it for several days until it has hardened
- Is the impression still there?
Now let’s make a sedimentary rock…or two
Here is what you do
- Place a layer of chocolate chips in the clear glass measuring cup, followed by a layer of peanut butter chips, followed by a layer of white chocolate chips.
- Place the cup in a sunny location or on top of a heating vent in your house –taking care not to mix the chips
- Leave the cup in a sunny location or on top of the heating vent until the chips begin to melt—but NOT to the point of becoming liquid
- Place the cup on a table or shelf where it can set for a few hours at room temperature
- When the chips have hardened, loosen the edges with the butter knife and remove from the measuring cup
- Do you see the different layers?
While a true sedimentary rock takes much longer to form, this gives you an idea of how it happens.