Science Study Guide for the GACE

General Information

The GACE Science testlet contains 30 questions to be completed in 45 minutes. All of the questions are multiple choice and assess science content and facts. You may see a few questions about laboratory safety, and these will probably begin with a scenario.

Earth Science

Earth Science is the branch of science that aims to study planet Earth. Since our planet is so complex and has many interrelated systems, Earth scientists usually focus on just one system at a time.

Earth Materials

Earth is made of many natural materials that form the land, oceans, and atmosphere. The most common materials include rocks, minerals, soil, water, and air. These materials are constantly changing through natural processes such as weathering, erosion, volcanic activity, and the rock cycle.

Water

Water covers about 71% of Earth’s surface and is essential for life on Earth, as well as many geological processes. About 97% of Earth’s water is salt water found in the oceans. The remaining 3% is freshwater, most of which is stored in ice caps, glaciers, and groundwater. A much smaller amount is found in lakes, rivers, and the atmosphere. Water helps regulate Earth’s global temperature, keeping it within a livable range. Water also provides one of the main forces of weathering and erosion that shapes Earth’s landforms.

Rocks

A rock is a naturally occurring solid material composed of one or more minerals or mineral-like substances. Rocks can be sedimentary, igneous, or metamorphic. Through the rock cycle, rocks can gradually change from one type into another.

Rocks can be described by physical properties such as their density, porosity (the amount of empty space), adsorption (the attachment of substances to a surface), absorption (the movement of substances into a material), capillarity (the movement of water through small spaces), and hardness. These properties are the result of the geological processes that rocks have undergone through history.

Fossils

Fossils are preserved remains, impressions, or traces of organisms that lived in the past. Examples include bones, shells, footprints, and burrows. Many fossils form when an organism or its traces are quickly buried by sediment and preserved as the sediment gradually becomes rock. Then, sediments start to build up over the remains to form rock. The original material may later decay and leave a mold, or minerals may replace or fill the remains and preserve their shape.

Soil

Soil is a mixture of weathered rock particles, organic matter, water, air, and living organisms such as bacteria.

Sand

Sand is made of small rock and mineral particles that have been broken down by weathering and carried by wind, water, or ice. Sand is commonly found on beaches, riverbanks, deserts, and the ocean floor. The color and texture of the sand varies from place to place because of the different parent material from which it came.

Earth’s Systems

The materials that are present on Earth are constantly moving and changing, making Earth a dynamic planet. Water moves throughout the planet, changing forms and shaping the Earth. Rocks and minerals form and are broken down through various processes. Elements that make up the Earth and atmosphere move through both the living and nonliving parts of the environment.

Hydrologic

Water moves through Earth’s hydrosphere through several processes. The basic water cycle includes evaporation from Earth’s surface, condensation in the atmosphere to form clouds, and precipitation when it falls back to the surface. When it reaches Earth’s surface, water can seep into the ground or become runoff that flows into the nearest body of water.

Weather determines the rate of evaporation as well as what type of precipitation will fall. Plants affect the water cycle by absorbing water that has infiltrated the ground, and releasing water vapor into the air through transpiration. Human activities such as paving surfaces can affect the amount of runoff, and climate change causes changes in precipitation patterns.

The movement of water across Earth’s surface as it moves from streams and rivers to lakes and oceans is a powerful force of erosion that shapes landforms such as canyons, valleys, caves, floodplains, deltas, and more. Humans can affect the natural flow and availability of water by building dams or diverting water from rivers and lakes for industry and community use.

Atmospheric

The atmosphere exists in several layers. Most of the mass of the atmosphere, and almost all weather, exists in the layer closest to the surface—the troposphere. Radiant heat from the sun drives weather patterns and powers the water cycle. The stratosphere contains the ozone layer, which absorbs harmful ultraviolet light from the sun and protects living things on Earth’s surface. The atmosphere becomes thinner as it gradually fades into outer space.

One important feature of the atmosphere is the greenhouse effect, in which gases such as water vapor, carbon dioxide, and methane absorb and re-radiate heat in the atmosphere. The natural greenhouse effect keeps Earth’s temperature within a range suitable for living things. Human activities, especially the burning of fossil fuels, are increasing the concentration of greenhouse gases and contributing to global climate change.

Geologic

Earth’s surface is slowly shaped over time by geologic processes. Earth’s outer layer is divided into tectonic plates that move slowly because of processes driven by heat within Earth’s mantle (the layer of Earth directly below the crust). As these plates separate or collide, they create landforms such as trenches, mountains, volcanoes, and rifts. Earthquakes also tend to occur along the boundaries between plates. The rock cycle is closely related to the movement of the plates; it describes the changes that occur as rocks form from lava, erode to create sediment, or transform through heat and pressure.

Weather

Weather is the state of the atmosphere in a given time and place. It is defined by a combination of elements such as air pressure, temperature, precipitation, humidity, wind, and cloudiness.

Air Pressure

Air pressure is the force exerted by the weight of air on a surface. In a low-pressure system, air often rises, cools, and forms clouds and precipitation. Storms, including hurricanes, are associated with low-pressure systems. In a high-pressure system, air generally sinks, which often produces clearer skies and calmer weather.

Temperature

Temperature can be affected by several factors. Places that are higher in latitude have lower average temperatures than those near the equator because the sun’s rays strike the surface at an angle. Locations near bodies of water tend to have fewer fluctuations in temperature than places further in the continent. Temperature is also affected by the movement of air masses that are moved around the surface by air currents.

Precipitation

Precipitation occurs when water returns to Earth’s surface in the form of rain, snow, sleet, or hail. Precipitation is also affected by air masses. Those that form over the ocean contain more moisture and are more likely to produce precipitation. Temperature and seasons also affect the rate and type of precipitation that occurs.

Humidity

Humidity describes how much water vapor is in the air. Warm air can hold more moisture than cold air. Relative humidity describes how much water vapor is in the air compared to how much water vapor the air can hold, based on its temperature. Humidity can make the temperature feel warmer to people, because it reduces evaporation through sweating making it more difficult to cool off.

Wind

Wind is caused by changes in air pressure. Air always moves from areas of high pressure to areas of low pressure. The greater the difference in air pressure, the stronger the wind will be. In addition to local wind patterns, Earth has a system of prevailing winds, belts of wind that circulate the Earth and distribute heat and moisture.

Cloudiness

Clouds form when water vapor in the air becomes cool enough to condense. Air pressure, temperature, and the movement of air masses contribute to the formation of various types of clouds.

Climate

Climate describes the long-term patterns and averages of weather conditions in a region, including temperature and precipitation. Climate is commonly determined using observations collected over a period of at least 30 years. These patterns include seasonal variation and help scientists classify regions into different climate types.

Equatorial

The equator receives a relatively constant amount of sunlight throughout the year. This produces higher average temperatures than in many other regions, with less temperature variation throughout the year. Equatorial regions that receive a lot of rainfall are tropical forests, which can support an abundance of plants and animals. Regions that do not receive enough rainfall to support trees may become tropical grasslands.

Desert

Deserts are very dry areas that receive less than 25 cm of precipitation per year. These arid climates may be located in tropical, temperate, or polar regions. Plants and animals that live here have special adaptations to prevent water loss.

Temperate

Temperate climates are found in regions that are between the equator and the poles. Some environments found here are deciduous forests with trees that lose their leaves in the winter, coniferous forests with trees that have needle-like leaves and remain green year-round, and grasslands, which are too dry to support a forest but have a variety of grasses and shrubs. Temperate climates experience seasonal changes.

Polar

The North and South poles receive sunlight at an angle, spreading the heat of the sun out over a larger area than regions nearer the equator. Polar regions typically have low precipitation since there is less evaporation occurring at low temperatures. The tundra is a cold, treeless biome with low precipitation and a short growing season. Polar areas have extreme seasonal changes during the year.