Science Study Guide for the GED Test

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Earth and Space Science Topics to Know for the GED

  • Interactions between Earth’s Systems and Living Things: matter, living and nonliving things, fossil fuels, effects of natural hazards (earthquakes, hurricanes, etc.), natural resources, sustainability.

  • Earth and its System Components and Interactions: atmosphere, climate change, oceans, the interaction between Earth systems, structure inside the Earth.

  • Structures and Organization of the Cosmos: structures in the universe, sun, planets, moons, tides, eclipses, Earth history, fossils, radiometrics, landforms.

Earth and the Universe

The Sun and Nuclear Fusion

The sun, like other stars, has nuclear fusion occurring at its core. The energy released by nuclear fusion reaches Earth in the form of light and heat. Stars with a mass similar to the sun can undergo nuclear fusion for an estimated ten billion years. Stars with more mass perform fusion faster and last less time. Less massive stars can last much longer than the sun. The energy released by the sun varies due to short-term phenomena, such as the 11-year sunspot cycle.

The Big Bang Theory

Several lines of evidence support the big bang theory:

  1. The observed expansion of the universe: Galaxies are moving away from each other. The more distance between them, the faster they are separating.

  2. The remnant radiation from the big bang called the cosmic background radiation

  3. The composition of ancient interstellar gas clouds matches the predictions from the big bang theory. The gases are mostly hydrogen and helium in the correct proportion.

Star Life Cycles

Stars produce elements heavier than hydrogen and helium. Heavier elements are produced by massive stars when they explode as supernovas. Elements increasing in heaviness up to iron are produced as a product of successive stages of nuclear fusion as stars go through their life cycle.


Johannes Kepler formulated laws of planetary motion that described the orbits of planets as ellipses. Later, Issac Newton derived a formula for gravitational force that is still used today to calculate the orbits of spacecraft and planets. The formula relates the force to the masses of the objects and the distance between them. It can be used to calculate the mass of an orbiting object if its speed is known or to predict the future position of an object.

Plate Tectonics

Several lines of evidence support the phenomena of plate tectonics. One example is the symmetry of the ages in rocks on either side of the mid-Atlantic Ridge. Rocks are youngest at the ridge and increase in age in either direction. Rocks the same distance from the ridge are the same age, no matter which side of the divide they are on. The presence of rocks and fossils of similar composition and ages on widely separated continents indicates that the continents were once joined.

Earth’s Formation and Early History

The formation and early history of the Earth can be inferred from studying minerals in the Earth and other planetary bodies. Some minerals can be dated back several billion years and tell of the early conditions. They can be compared to minerals recovered from meteorites. Some meteorites are remnants of the early solar system. The abundance of craters on other bodies, such as the moon, indicates that violent collisions must have been common in the early solar system.

Systems of the Earth

Earth Processes

The Earth’s features result from the interplay between destructive and constructive geologic forces. Destructive forces include weathering, erosion of rocks, and the erosion of coastline by the ocean. Volcanoes and plate tectonics can form new land masses, and colliding plates can cause the uplift of mountains (orogeny).

Geoscience Data Analysis

Geoscience data can create models that show relationships among Earth’s systems; for example, ocean currents affect the atmosphere and weather of the nearby continents. Changes to the atmosphere that increase the temperature can melt glacial ice in Greenland and disrupt currents in the North Atlantic, affecting the climate of coastal Europe.

Thermal Convection

Observing seismic shock waves around the Earth has helped build a model of the Earth’s interior. This model shows a molten core and a hot, semi-fluid mantle with cyclic convection currents. These convection currents drive the plate tectonics of the Earth’s crust. Other studies, such as the changing magnetic field and laboratory experiments, have contributed to our understanding of the Earth’s interior.


On a large scale, the Earth’s climate results from the balance between energy input and energy lost. The primary energy input to the atmosphere is from the sun, which can vary over short and long time scales. On shorter time scales, events that reduce the amount of sunlight hitting the Earth’s surface, such as volcanic eruptions, can cool the climate. On somewhat longer timescales, changes in atmospheric composition and the ocean’s circulation can cause changes. Extremely long-term fluctuations are caused by changes in the Earth’s orbit, the tilt of its axis, and the sun’s output.

Water and the Water Cycle

Water has an incredibly profound effect on the rock cycle of Earth. As a chemical agent, it can slowly dissolve rocks over the centuries. Flowing water can erode rock much more quickly. The unique property of water to expand as it freezes allows it to crack rock as it freezes in crevices. The water content of magma has a dramatic effect on its melting point. Magma with higher water content melts at lower temperatures. The resulting motion of differently heated magmas contributes to an area’s geothermal activity.

Atmospheric Changes and the Carbon Cycle

The transfer of carbon dioxide into and out of the atmosphere is a topic important to climate change. Quantitative models of the carbon cycle will show reservoirs and transfers. A reservoir is a particular form and location of carbon. For example, carbon dioxide in the atmosphere is a reservoir, and carbonate compounds in seawater are another. Transfers show how fast carbon moves between reservoirs.

Earth Changes

The evolution of life is affected by geochemical conditions on Earth; and in turn, life can alter these conditions. The early Earth had very little oxygen in the atmosphere. This limited life to inefficient modes of cellular respiration. When photosynthetic organisms developed, their activity added oxygen to the atmosphere. This allowed for the development of aerobic respiration and larger, multicellular creatures.

Humans and the Earth

Humans have reached a stage of technological development where our actions can affect the environment faster than natural processes can adjust and quicker than biological evolution. Understanding these processes and how our activities affect them is essential to make informed decisions.

Natural Resources and Hazards

Human activity depends on favorable access to resources and minimal impact from hazards. Areas with access to clean, fresh water and good soils are advantageous. We can compensate for deficiencies of these resources, but there is an economic cost. Areas of low impact from natural disasters and severe weather are favored because we have minimal control over these events.

Resource Management Costs

Resource management must consider all costs and impacts along the entire chain involving that resource. For example, there may be costs involved to enact soil conservation measures. However, this must be weighed against the cost of not conserving the soil: lost agricultural productivity, costs and impacts of producing and applying fertilizers, loss of a non-renewable resource, etc. Decisions should be based on this type of comprehensive cost-benefit analysis.


Sustainability is the balance between the use of a resource and the ability to replenish that resource. For non-renewable resources, practices such as recycling may allow these resources to last indefinitely. These same practices may help to keep the use of renewable resources low enough to allow them to replenish and keep up with demand. Other factors that can improve sustainability are increased efficiency and the development of new technologies.

Human Impact

Humans impact natural systems in many ways. Solutions to limit the impact of human activities need to be tailored to specific areas. Solutions can range from local activities, such as the restoration of a particular habitat, to global ones, such as limiting carbon emissions. Effective solutions come from a comprehensive understanding of the natural systems and a corresponding understanding of human activities.

Global Climate Change

Data providing evidence for climate change comes from various sources, such as glacial core samples to determine previous atmospheric conditions, data on current and past industrial emissions, and laboratory data on the behavior of carbon dioxide. These data can be assembled into predictive models that give insight into the potential changes in temperature, precipitation, and sea level.

System Models

Earth’s major systems can be represented with sophisticated models showing their relationships. These models can aid in understanding and mitigating the effects of human activities. For example, land use practices in a large region may seem to only affect terrestrial ecosystems. However, widespread changes could affect how much solar radiation is reflected or absorbed and thus influence the atmospheric system and weather patterns.

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