5.7A The student can explore the processes that led to

the formation of sedimentary rock and fossilfuels

Explanation:

Although students have studied the changing surface of Earth in prior grades, this is the first time students will consider changes to Earth’s surface that occurred millions of years ago, and how those impact the formation of sedimentary rocks and fossil fuels.

Key Concept 1: Sedimentary rock is formed over millions of years from the deposition of sediment in layers.Sediment layers on top apply pressure to those on the bottom, compacting them into sedimentary rocks. Sedimentary rock represents one of three rock groups formed on Earth. In fifth grade, students focus only on sedimentary rock formation because fossil fuels are formed within these rock layers. Sediments are loose particles of inorganic material, such as pebbles or sand. These sediments wash down slopes into bodies of water, such as rivers, lakes, or oceans, where they settle to the bottom.

Layer after layer of sediment is deposited, after which two processes can occur that form sedimentary rocks:

(1) Compaction, where the particles are squeezed together by the weight of the layers of sediment above them, and

(2) Cementation, where the minerals in water fall out of suspension around the particles and act as glue, sticking the sediments together. Sandstone and shale are examples of sedimentary rock.

Key Concept 2: Fossil fuels are formed over millions of years from the deposition of organic materials in layers.

Sometimes organic matter (remains of dead plants or animals) sinks in water, and is buried in layers of sediment. The organic material begins to decay from the pressure and heat generated from the layers above them, and can become fossil fuels. Coal, oil, and natural gas formed millions of years ago, and are burned today as energy sources for electric power plants, furnaces, stoves, cars, etc.

Two types of ancient sedimentary rock formations are the sources of all fossil fuels.

Coal Formation - First, in ancient swamps, prehistoric plants and trees began to die 300 million years ago during the Carboniferous period, long before dinosaurs appeared. In the swamps, plant remains were covered with soil, layer upon layer. A thousand years of heat and pressure slowly turned these compacted, decayed plant layers (organic matter) into peat. It took hundreds of millions of years more for heat and pressure deep within Earth to turn peat into coal.

Oil and Gas Formation - A second type of sedimentary rock formation occurred at the bottom of ancient oceans and seas when tiny marine animals called “plankton” died, sank, and were covered with layers of sand. Millions of years of heat and pressure turned this organic matter into oil and natural gas trapped in layers of sedimentary rock.

Nonrenewable Resources - Because the remains of ancient plants and animals are sources for these fuels, they are called fossil fuels. Nature is not replenishing this supply of fuel, so coal, oil, and natural gas are considered nonrenewable resources. The pollution produced from burning fossil fuels has led to an increased interest in alternative energy sources, which is studied in more detail in a subsequent scope.

Key Concept 3: Fossil fuels are formed in sedimentary rock layers when materials are compressed and heated deep under the Earth’s surface.

Geologists who look for sources of fossil fuels study sedimentary rock layers and have learned that rock layers tell a story about the events that led to fossil fuel formation.

Other things students should know:

  • Oldest layer of rock formations (and oldest fossils) are the bottom layer
  • Youngest layer of rock formations (and youngest fossils) are the top layer
  • Heat, pressure and millions of years are necessary for sedimentary rock and fossil fuel formation
  • Five steps are:
  • Weathering
  • Erosion
  • Deposition
  • Compaction (compression)
  • Cementation (solid rock)

(They learned a song and dance to help them remember!)

  • The Sun’s energy contributes to fossil fuels by providing the energy to the plants/animals that are trapped in the rock layer, which can be burned later

(4th Grade) TEKS 4.7A- The student can examine properties of soils, including texture and color, capacity to retain water, and the ability to support the growth of plants.