Earth Materials

Once students understand how weathering and erosion act on Earth’s surface, students turn toward the energy within Earth’s interior that powers plate tectonics, which in turn shapes Earth’s surface and, along with weathering and erosion, contributes to the cycling of Earth materials. 

• Many changes to Earth’s surface are powered by energy deep within Earth, which flows outward to the surface because of heat transfer. 
• Convection in the mantle causes Earth’s tectonic plates to move and interact with one another.
• The lithosphere is broken into slabs of solid rock called tectonic plates, which are constantly moving and interacting to create many of the landforms of the planet.
• As the tectonic plates move and interact with one another, they contribute to the cycling of Earth materials over time.
  
  

• How is Earth’s structure related to the transfer of energy from the interior of the planet outward toward the surface?
• How is the movement of Earth’s mantle similar to the movement of wind and deep ocean currents?
• What causes the heat imbalance that causes convection in the mantle?
• How does the thermal energy in the mantle’s convection change matter?
• What is one way that tectonic plates interact?
• What is the relationship between the formation of mountain ranges and the movement of the tectonic plates?
• How is the movement of tectonic plates related to the cycling of Earth materials?
  
  

Misconception: Earth’s surface is static and unchanging.

Fact: Earth’s surface is constantly changing through a variety of processes, including plate tectonic movement, weathering, and erosion.

Misconception: Weathering and erosion are the same.

Fact: Weathering describes the breakdown of rock into smaller pieces. Erosion describes the transport of those smaller pieces and other sediment by wind or water.

Convection : heat transfer in fluids (liquids and gasses) where warmer, less-dense fluid rises, allowing cooler, denser fluid to take its place; causes a tumbling motion in the fluid

Convergent Boundary : a plate boundary formed when two tectonic plates move toward one another perpendicular to the fault line

Crust : Earth’s outermost layer; the hard rock layer of the planet that makes up the continents and holds the oceans

Divergent Boundary : a plate boundary formed when two tectonic plates move apart from one another perpendicular to the fault line

Igneous Rock : a category of rock formed when hot liquid rock (either magma of lava) cools into solid form

Inner Core : the hottest layer inside Earth; made of a mixture of solid iron and nickel

Mantle : the layer of Earth between the outer core and the crust; mostly molten, semi-solid rock called magma that is so soft it moves in convection currents, like liquid water

Metamorphic Rock : a category of rock formed in chemical reactions where one type of rock is changed by pressure or heat into a new type of rock with different properties

Outer Core : the outer layer of Earth’s core; made of liquid iron and nickel metal

Rock Cycle : the processes that form, break down, and re- form rock from one category to another

Sedimentary Rock : a category of rock formed from layers of sand, soil, clay, gravel, and other sediment that built up in one location over time

Tectonic Plates : drifting slabs of solid rock, called plates, that make up Earth’s surface

Transform Boundary : a plate boundary formed when two tectonic plates slide past each other in parallel, grinding along their sides as they move

Collecting Rocks

For his job, Dr. Randy Keller has traveled to every continent on the planet, including Antarctica, where he would camp out for two months at a time. He has taken a research vehicle and descended into the deep, dark ocean. From the darkness, he saw brightly lit organisms swim past his window. He has also traveled to Hawaii, where he saw lava flow down a hillside and then cool into solid rock in front of his eyes.

Dr. Keller is a geologist who studies volcanic rocks to learn more about Earth’s structure. A volcano is a structure formed around a hole in Earth’s crust that releases magma, which is molten, semi-solid rock. When magma reaches Earth’s surface, it is called lava.

Dr. Keller studies volcanic rock to answer several questions. How old is the volcano? How deep within Earth’s interior did the lava come from? What did the lava interact with on its way to the surface?

One of the challenges to studying geology is that many changes on Earth happened a long time ago. Another challenge is that the deepest any machine has drilled into the planet is 12 kilometers—nowhere near the center. Most of what we know about the inside of our planet comes from scientists who study volcanic rock, earthquakes, and meteorites.

Cycling of Earth Materials

Sometimes, the movement of the tectonic plates causes vents to open up in Earth’s crust. The vents allow magma from the mantle to seep through, forming volcanoes.

The vents that allow magma to escape and form volcanoes are typically found on the edges of moving tectonic plates. Volcanoes also form on the ocean floor where the crust is thinner, and so can crack more easily. Volcanoes produce the newest land on Earth. The islands of Hawaii were built up from volcanoes on the ocean’s floor that erupted and cooled to form habitable land.

When volcanic eruptions reach Earth’s surface, they bring with them mounds of volcanic material that eventually cool and harden into a kind of rock called igneous rock. The word igneous means “from fire.” Igneous rock forms when magma or lava from Earth’s mantle cools into solid form. This kind of rock is what Dr. Keller focuses on. Volcanoes form because of Earth’s tectonic plates.

In addition to igneous rock, there are two other categories of rock: metamorphic rock and sedimentary rock. Metamorphic rocks are rocks formed in chemical reactions where one type of rock is changed by pressure or heat into a new type of rock with different properties. The movement of Earth’s tectonic plates can cause rocks to get pushed down deep into the crust. There, the heat and pressure of all the weight on top of them cause the chemical reactions. Sedimentary rocks are formed from layers of sand, soil, clay, gravel, and other sediment that built up in one location over time. The pieces of sediment are carried by the wind and rain to settle on the ground or in the lakes and oceans. Over thousands or millions of years, the pressure of more and more layers of sediment compresses the layers of sediment into solid rock. Because of this, the oldest sediment forms the bottom-most layers of the rock. Newer layers replace older layers at the top.

Rocks are always changing. The changes often happen slowly, over thousands or millions of years, but nearly all of the crust that you see today will someday be returned to Earth’s mantle. All of the rocks that are on Earth today are made of the same matter that existed when dinosaurs roamed. But the matter is reshaped and re- formed over millions of years into new rocks with different properties. For example, rocks break down into sediment. That sediment can collect in layers. Over time, heat and pressure can compress the layers of sediment into new sedimentary rock. Or tectonic plates can push the sediment deep into Earth’s crust. There, it can undergo chemical reactions that change its properties, turning it into metamorphic rock. Eventually, any rock pushed deep into Earth’s interior will melt into magma. If magma reaches the surface, it will cool and harden into rock again. All rocks on Earth’s surface are weathered and eroded. The processes that form, break down, and re-form rock from one category to another are called the rock cycle.

For the hands-on activity of this lesson, students develop models to experiment and figure out how energy within Earth’s interior powers the phenomena of plate tectonics, which in turn drives the phenomena of cycling of materials on Earth’s surface. Students use their models to analyze the cause-and-effect relationship between convection in the mantle and the movement of Earth’s tectonic plates.