12.3 Earth, Space, and Environmental Systems

Earth and Space as Test Contexts

Earth and Space Science makes up roughly 20% of GED Science, about 7 of the 34 questions, sitting alongside Life Science and Physical Science (each 40%). These topics are not just facts about rocks and planets; they are contexts for reasoning from evidence, reading models, comparing data, and judging claims about natural systems. You need broad familiarity with the big ideas, not college-level depth.

A typical Earth/Space item supplies a stimulus and asks you to use it: a diagram of tectonic plates, a table of hurricane wind speeds, a map of ocean currents, a model of the Moon's orbit, or a passage comparing energy sources. The correct answer is the one the stimulus actually supports, so resist the urge to answer from memory when the data are in front of you.

Earth-System Map

Interactions and Cycles

Earth's systems feed back on one another. Heavy rain (atmosphere) causes flooding (hydrosphere), which erodes soil (geosphere) and destroys habitat (biosphere). Burning fossil fuels removes carbon-rich material from the geosphere, adds carbon dioxide to the atmosphere, and shifts climate patterns that affect living systems. When an item asks what happens after one process changes, trace the matter or energy step by step through the connected systems.

Cycles are frequent GED contexts. In the water cycle, evaporation, condensation, precipitation, runoff, and infiltration move water among the systems. In the carbon cycle, photosynthesis, respiration, decomposition, ocean exchange, and combustion shuttle carbon between living and nonliving reservoirs. If burning increases and photosynthesis stays flat, atmospheric carbon rises, the predictable answer a tracing question is looking for.

Natural Hazards and Mitigation

A natural hazard is an event such as an earthquake, hurricane, wildfire, flood, drought, volcanic eruption, or landslide that can harm people or ecosystems. GED items may probe frequency, severity, short- and long-term effects, or mitigation. Mitigation means reducing risk, not eliminating every hazard: stronger building codes reduce earthquake damage, storm shelters reduce tornado deaths, and restored wetlands absorb floodwater. The trap answer always says a measure "eliminates" or "stops" the hazard, which mitigation never claims.

Resources and Sustainability

Environmental items often compare resource choices. Renewable resources replenish on a human time scale, sunlight, wind, flowing water, and sustainably managed forests. Nonrenewable resources form so slowly that human use depletes them, including coal, oil, natural gas, and most mineral ores. But sustainability is more than the renewable/nonrenewable label. Solar panels burn no fuel yet carry mining and disposal costs; hydroelectric dams give renewable power yet block fish migration and alter rivers. The best GED answer weighs the whole table of trade-offs, not a single positive feature.

Space Models

Space items lean heavily on diagrams. Moon phases depend on the Moon's position relative to Earth and the Sun. Tides arise mainly from gravitational pulls among Earth, the Moon, and the Sun, with the highest (spring) tides when the three roughly align. Eclipses occur when Sun, Earth, and Moon line up: a solar eclipse puts the Moon between Earth and Sun, while a lunar eclipse puts Earth between Sun and Moon. For stars, galaxies, and Earth's age, the item supplies the data, you compare star brightness, sequence a star's life cycle from a chart, or read evidence from fossils, rock layers, or radiometric dating.

Treat each model as evidence: identify what it shows, then choose the claim it supports.

Weather, Climate, and Plate Tectonics

Two Earth topics appear often enough to learn cold. First, weather is short-term (today's temperature, this storm) while climate is the long-term average of a region over decades; a single cold day is not evidence against a warming climate trend, and items test exactly that confusion. Second, plate tectonics explains earthquakes, volcanoes, and mountain building: plates pull apart at divergent boundaries, collide at convergent boundaries, and slide past each other at transform boundaries (where many earthquakes occur). Fossils of the same species on two now-separated continents are classic evidence that the plates once joined.

Renewable vs. Nonrenewable at a Glance

When an item asks for the most sustainable choice, the correct answer usually balances energy output against the environmental cost shown in the passage, rather than picking the option that is merely labeled renewable.

A related trap is treating pollution as a single thing. Air pollution (smog, greenhouse gases), water pollution (runoff, oil spills), and land pollution (waste, mining tailings) each move through a specific Earth system, and an item may ask which system a pollutant first enters and where it travels next. Trace it the same way you trace a cycle: source, system entered, system affected downstream.