Modeling Sedimentary Rock Formation
An Elementary Lesson
Teacher Directions:
In this activity, students will create a model of geologic time while engaging with an interactive story
about how sedimentary rock helps form fossil fuels. At the end of the activity, students will be able to
label the geologic layers formed when sediment deposits over time.
Materials Needed:
Container: Any clear container works, as long as the kids can see the layers. Clear, 16 ounce plastic cups
are an excellent option. Groups can label an extra one cup “Time, Heat, and Pressure” and after each
layer, compress the “sediment” down with the “Time, Heat, and Pressure” cup to model the effects of
time, heat, and pressure.
Sediment Layers: 6 sediment layers with contrasting colors. The following are suggestions. Use what
materials are available at minimal or no cost.
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Layer 1: Sand
Sea Life: Gold Fish Crackers
Layer 2: Sand mixed with Flour works well to show a color change
Layer 3: Sand and Potting Soil mixture
Swamp plants: ferns or grass clippings work well or use cut/torn pieces of green construction
paper
Layer 3: Potting Soil
Layer 4: Potting Soil mixed with either clay or Tree Bark mulch
Layer 5: Tree Bark mulch
Forest life: Bear shaped graham crackers and dry leaves work well. Around Halloween, bone
candy (like Sweet Tarts®) is available and can be mixed with the dried leaves
Layer 6: Regular dirt/soil or clay
Layer 4: (Suggestions for sediment layers: sand, sand mixed with potting soil, gravel, potting soilmix
together sand, clay, potting soil, gravel, etc.) create a good visual color scheme. Switch darker and
lighter sediment layers to achieve a good visual.
Sea life- goldfish snacks mixed with sea toys.
Extension:
Fossil pictures or examples can be displayed and discussed when creating layers.
Introduction: (Read to Students, Feel Free to Be Dramatic)
Today we are going to explore the history of our land and how sedimentary rock was formed. During
this investigation we will also see how fossils were created. Later on you will use this investigation to
see where fossil fuels were created.
The Earth was formed about 4.6 billion years ago. It was a red hot sea of molten rock then, all magma.
When the Earth started to cool, rocks were formed. The oldest rocks found are about 3.9 billion years
old and the processes of landform formation (weathering, erosion, deposition) started to shape our
Earth.
Our story takes place where the United States is today, very close to where we are right now. About 350
MYA (million years ago) our land we know today as the United States was mostly covered by a shallow
sea.
(Drop in sediment layer 1)
Strange sea life swam all around, some humongous alien looking creatures, some microscopic –you
need a microscope to see it.
(Add Sea Life)
Millions of years went by and the sea was abundant with life. When the animals would perish their
bodies would fall to the sea floor to be buried by layers and layers of sediment.
(Drop in sediment layer 2)
After another 50 million years the seas dried up.
(Drop in sediment layer 3)
Swampy land full of monstrous plants took over the land. These plants lived and died and when they
died they fell into the swamp waters and settled on the swamp floor.
(Add swamp plants)
The ferns were the size of trees back then. Time continued to move forward and millions of years of
weathering, erosion, and deposition brought many layers of sediment to cover the land.
(Drop in sediment layers 4 and 5)
Eventually, the swamps dried up and forests grew and mammals took over the land
(Drop in forest life).
When the animals died they were buried by sediment.
(Drop in sediment layer 6)
Most of the time, the animals decomposed and formed new soil, but sometimes the conditions were
just right and fossils of the animals were formed.
(Show fossil pictures)
Time went on and on and as the sediment layers continued to build up there was a lot of force pushing
the layers together and with heat and a lot of time these layers started to cement together forming
rocks, this type of rock is call Sedimentary Rock. Why do you think it is called that? *******
This has been a sedimentary rock story, giving the history of sedimentary rock formation. Revisit this
display when you learn about oil and coal formation so you can see where it happened.
Suggestions:
Using small post-it tabs, students can label the ocean layer at 350mya, the swamp layer at 300mya, and
the forest layer at 100mya those times coincide with oil and coal formation –oil in the ocean, coal in the
swamp)
The following pictures will be helpful to illustrate for students what the world looked like throughout
portions of the story.
A Geologic Cross-Section of Earth’s History
The United States ~ 350 Million Years Ago
Shallow, Inland Sea
Ancient Swamp
Mammals Rule the Land
Fossils
Sedimentary Rock Formations
Test Your Knowledge: Sedimentary Rocks
What layer is the oldest?
How do you know?
Sedimentary Rock Formation
Vocabulary
The process of sedimentary rock formation takes millions of years to complete only to begin
a new cycle of rock formation.
Sedimentary rock formation: begins with igneous, metamorphic, or other sedimentary
rocks. When these rocks are exposed at the earth’s surface they begin the long slow but
relentless process of becoming sedimentary rock.
Weathering: all rocks are subject to weathering. Weathering is anything that breaks the
rocks into smaller pieces or sediments. This can happen by the forces of like wind, rain, and
freezing water.
Erosion: the combination of weathering and movement of the resulting sediments is called
erosion.
Deposition: sediments that form from these actions (weathering and erosion) are often
carried to other places by the wind, running water, and gravity. As these forces lose energy
the sediments settle out of the air or water. As the settling takes place the rock fragments
are graded by size. The larger heavier pieces settle out first. The smallest fragments travel
farther and settle out last. This process of settling out is called deposition.
Lithification: the changing of sediments into rock. There are two processes involved in this
change. They are compaction and cementation.
Compaction: occurs after the sediments have been deposited. The weight of the sediments
squeezes the particles together. As more and more sediments are deposited the weight on
the sediments below increases. Waterborne sediments become so tightly squeezed together
that most of the water is pushed out.
Cementation: happens as dissolved minerals become deposited in the spaces between the
sediments. These minerals act as glue or cement to bind the sediments together.
Types of Sedimentary Rock
Breccia
Breccia is a clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The
spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds
the rock together. The specimen shown above is about two inches (five centimeters) across.
Chert
Chert is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO 2). It occurs
as nodules and concretionary masses and less frequently as a layered deposit. It breaks with a conchoidal fracture,
often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting
tools and weapons. The specimen shown above is about two inches (five centimeters) across.
Coal
Coal is an organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a
swamp environment. Coal is combustible and is often mined for use as a fuel. The specimen shown above is about
two inches (five centimeters) across.
Conglomerate
Conglomerate is a clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded
particles. The space between the pebbles is generally filled with smaller particles and/or chemical cement that bind
the rock together. The specimen shown above is about two inches (five centimeters) across.
Iron Ore
Iron Ore is a chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances)
combine in solution and deposit as a sediment. Hematite (shown above) is the most common sedimentary iron ore
mineral. The specimen shown above is about two inches (five centimeters) across.
Limestone
Limestone is a rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of
shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or
ocean water. Limestone is used in many ways. Some of the most common are: production of cement, crushed stone
and acid neutralization. The specimen shown above is about two inches (five centimeters) across.
Rock Salt
Rock Salt is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is also
known by the mineral name "halite". It is rarely found at Earth's surface, except in areas of very arid climate. It is often
mined for use in the chemical Industry or for use as a winter highway treatment. Some halite is processed for use as
a seasoning for food. The specimen shown above is about two inches (five centimeters) across.
Sandstone
Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering
debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas.
The specimen shown above is about two inches (five centimeters) across.
Shale
Shale is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering
debris. It typically breaks into thin flat pieces. The specimen shown above is about two inches (five centimeters)
across.
Siltstone
Siltstone is a clastic sedimentary rock that forms from silt-size (between 1/256 and 1/16 millimeter diameter)
weathering debris. The specimen shown above is about two inches (five centimeters) across.
Some Common Sedimentary Rocks
Name
Image
Color
Composition
Sandstone
Red or Gray
Sand grains cemented
together
Limestone
White to Gray
Calcite and sometimes
fossils
Shale
Dark Gray
Compacted mud
Conglomerate
Different
Colors
Rounded cobbles and
pebbles cemented
together