Holt Environmental Science: The Dynamic Earth

The Dynamic Earth

Layers of the Earth

• The physical structures and chemical properties of the solid Earth provide evidence of Earth’s evolution over time. Investigation of Earth’s layers, tectonic activity, and the rock cycle reveals Earth’s history. As Earth cooled and formed a planet, less dense elements and compounds separated and formed layers around a dense core.

  
  

• Earth contains distinct layers, including the inner core, outer core, mantle, crust, asthenosphere, and lithosphere. When constructing a model of the layers of Earth, chemical composition, state of matter, and thickness of each layer should be considered.

Layers of the Earth

The Earth has many layers but the main ones include the crust, mantle (upper and lower) and the core (inner and outer). The outer core is liquid and surrounds the inner core which is solid.

Layers of the Earth: The Core

• At the very center of Earth is its core. The core is made up of very dense elements, such as iron and nickel. The outer portion of the core is molten (liquid) while the inner portion is solid. This difference in state divides the core into two regions: the outer core (liquid) and the inner core (solid). The inner core is solid because at the center of Earth, there is so much pressure it is impossible for the iron to melt.

Layers of the Earth: The Mantle

• Directly above the core is the mantle. The mantle makes up the majority of Earth’s volume. The mantle is composed of rocks known as silicates. The state of matter within the mantle varies from a brittle, solid state to a soft, molten state, somewhat like Silly Putty

Layers of the Earth: The Crust

• The very top layer of Earth is the crust, which is relatively quite thin when compared to the other layers of Earth. The crust is either continental (where the surface is land) or oceanic (where the surface is under the ocean). Most of the rocks in the crust are made up of lighter elements, such as silicates combined with aluminum, calcium, magnesium, potassium, and sodium. The crust has very little iron.

Multiple Choice

Which of the following models would best represent the inner and outer core of Earth, based on the physical characteristics of each layer?

• A metal ball bearing (solid) suspended in oil (liquid)

• Gelatin (red semi-solid) on top of a cracker (brittle solid)

• A ball of clay (solid) filled with water (liquid)

• Rubber ball (flexible) painted red (thin solid covering)

Multiple Choice

Oceans and other bodies of water, are found on which layer of the Earth?

• Outer Core

• Mantle

• Inner Core

• Crust

Multiple Choice

Which of the following would be an accurate feature to include in a model of Earth?

• A crust that is the thickest layer

• An inner core that contains oceans

• A thin mantle in the center of the model

• A liquid outer core below the mantle

Classifying Rocks

• The physical structures and chemical properties of the solid Earth provide evidence of Earth’s evolution over time. Investigation of Earth’s layers, tectonic activity, and the rock cycle reveals Earth’s history. As rocks move through the rock cycle their mineral compositions and physical structures change to reflect the processes under which they are formed.

• Over time through the various Earth processes of weathering, erosion and deposition (sedimentary rock), melting and crystallization (igneous rock), and heat and pressure (metamorphic rock), Earth’s rocks change from one type into another as described in the rock cycle.

Igneous Rocks

• Igneous rocks are formed when lava or magma cools and solidifies. They are characterized by interlocking mineral crystals that vary in size depending upon how rapidly they cooled

Sedimentary Rocks

• Sedimentary rocks are formed when particles of other rocks are deposited in layers and undergo compaction (crushing together), and cementation (binding of the sediments). Some sedimentary rocks contain fossils.

Metamorphic Rocks

• Metamorphic rocks are formed deep underground where heat and pressure cause existing rocks to be changed. Metamorphic rocks are often characterized by wavy layers of mineral crystals or by the presence of unusual minerals.

Multiple Choice

What is the primary process that turns sediments into sedimentary rocks?

• Organisms walking on layers of sediment, pressing particles together tightly

• Minerals with sediment, absorbing water and undergoing a chemical reaction

• Upper layers of sediment, pressing down on lower layers of deposited sediment

• Magma cooling under the surface of Earth, crystallizing to form rock

Multiple Choice

The interlocking crystals of an igneous rock help to classify it since these crystals are evidence of how the rock formed. The crystals are a result of –

• quartz coming of solution

• particles forming layers

• chemical reactions of minerals

• melted rock that cooled

Multiple Choice

Metamorphic rocks are different from igneous and sedimentary rocks in that metamorphic rocks form –

• when liquid rock freezes into a solid

• by magma rising from Earth’s core

• from existing rock that has been changed

• by layering minerals of different sizes

Plate Tectonics

• Plate tectonics provides the driving force for changes on Earth’s surface, Earth’s layers, and the rock cycle. The lithosphere is broken into separate rigid plates that contain dense oceanic crust and less dense continental crust. The plates float and move slowly on Earth’s soft, underlying asthenosphere, driven by convective currents.

Plate Tectonics

• The motion of tectonic plates results in significant and often dramatic interactions along the plate boundaries. The types of plate motion are classified as divergent (pulling apart), convergent (pushing together), or transform (side by side interaction).

  
  

• Geologic events and landforms are used to locate and classify plate boundaries as well as to measure the rate of plate movement. Evidence of plate movement includes volcanic eruptions, mountain chains, earthquakes, blocks of sinking crustal material, oceanic trenches, and the formation of new crustal rock along spreading ridges.

Tectonic Plate Boundaries

Multiple Choice

At which type of boundary illustrated below is a trench most likely to form?

Multiple Choice

An image of the relative motion at a tectonic plate boundary is provided. What event will occur at the boundary shown?

• Mountain formation

• An earthquake

• Trench formation

• Volcanic island formation

Multiple Choice

What event will most likely occur at a divergent plate boundary?

• The plates will most likely occur at a divergent plate?

• One plate will subduct under the other

• The plate will form an ocean basin

• A fault line will form and earthquakes will result

Elements and Compounds

• Matter has mass and takes up space. Mass measures how much matter is present and volume measures how much space the matter occupies. Matter occurs as elements, compounds, or mixtures.

  
  

• An element is a pure substance that cannot be broken down into simpler different substances. A sample of an element may contain many atoms that are all the same; an atom is the smallest particle of a substance that maintains consistent properties used to identify an element.

Elements and Compounds

• Matter is considered a pure substance when it is uniform throughout and has consistent properties. Elements, made of a single kind of atom, are pure substances. Compounds, made of two or more kinds of atoms bound together, are also pure substances. Mixtures, made of a blend of elements and compounds, are not pure substances because they do not have consistent properties.

Elements and Compounds

• Elements are represented on the periodic table of elements with one or two letter chemical symbols, such as O for oxygen or Si for silicon.

• Compounds consist of atoms of different kinds of elements that are bound together. Compounds are represented by a chemical formula.

• The solid Earth, the lithosphere, is made of a limited number of elements and is primarily comprised of oxygen and silicon.

Elements and Compounds

• Earth’s living matter, the biosphere, is made of a limited number of elements and primarily comprises oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.

• Earth’s oceans, part of the hydrosphere, are made of a limited number of elements and primarily comprise oxygen and hydrogen, the two elements in pure water.

• The atmosphere is made of a limited number of elements and primarily comprises nitrogen and oxygen.

Multiple Choice

Which of the following is the most abundant element in the Earth's crust?

• Calcium

• Iron

• Oxygen

• Potassium

Multiple Choice

Which of the following three elements are most abundant in the plants and animals that make up the biosphere?

• Sulfur, oxygen, and hydrogen

• Nitrogen, silicon, and oxygen

• Phosphorous, oxygen, and iron

• Oxygen, carbon, and hydrogen

Multiple Choice

Use the chart to answer the following question. A student is given the chart above and is told to identify an unknown mineral. The student observes that the mineral has a glassy luster and a hardness less than 3. What is the identity of the mineral?

• Actmite

• Cobaltite

• Jadeite

• Talc

Weathering/Erosion/Deposition

• Weathering is the gradual chemical and physical changes made to rocks due to the presence of weathering agents such as water, temperature changes and the actions of plant roots that pry rocks apart.

• Erosion occurs when the rock or soil of Earth’s surface is moved to another location by erosional agents such as the flow of water, ice or wind, as well as the constant pull of gravity. If the sediments deposited are sand particles, such as in a

  beach environment, sand bars form.

• Deposition occurs as sediment or fine rock fragments, resulting from the actions of weathering and erosional agents, settles (or is deposited) in a different location.

Multiple Choice

High rains cause the flow in a river to increase. The increase in the river’s flow will most likely have which of the following effects on the environment?

• The banks of the river will experience increased erosion

• The river will deposit less material onto its delta

• The path of the river will become more crooked

• The river will dry out completely in a few days

Multiple Choice

What is a possible side effect of severe beach erosion?

• Deltas will increase in size

• Boulders will be carried inland

• Sand bars will form offshore

• Canyons will be created nearby