GED Science Test: Earth’s Hydrosphere

By Murray Shukyn, Achim K. Krull

To ensure you are prepared for the GED Science test, you need to familiarize yourself with the Earth’s hydrosphere. Earth’s hydrosphere consists of all its water in every form — ice, snow, water, and water vapor. It includes surface water (oceans, lakes, rivers, streams, and puddles), water in and below the ground (groundwater, wells, and aquifers), and water in the air (clouds, rain, snow, and fog).

The movement of water is referred to as the water cycle, a continuous process in which water evaporates from the Earth’s surface, condenses to form clouds, and falls back to Earth in some form of precipitation. The water cycle also involves the movement of water in the form of rivers, streams, and ocean currents.

Note these important distinctions in water cycle lingo:

  • Condensation: The process of changing from a vapor or gas into a liquid.

  • Evaporation: The process of changing from a liquid into a vapor or gas.

  • Precipitation: The product of condensation, which is released from clouds in the form of rain, snow, sleet, or hail.

  • Transpiration: The transportation of water through plants from roots to small pores on leaves, where the water is converted to vapor.

Various natural forces power the water cycle, including the following:

  • Chemical properties of water: Differences in water densities due to temperature and salinity contribute to the formation of ocean currents. For example, colder, saltier water is denser than warmer, fresh water, causing it to sink, producing currents.

  • Earth’s rotation: As the Earth spins on its axis, it deflects winds and currents, a phenomenon called the Coriolis effect. Earth’s rotation combined with air and water movements cause a circular, spinning motion. North of the equator, storms tend to rotate clockwise. South of the equator, they tend to spin counterclockwise.

  • Earthquakes: Earthquakes can displace vast amounts of water.

  • Gravity: Gravitational fields surrounding the Earth and moon interact to cause currents to rise and fall, and the gravity on Earth causes water to flow in rivers and streams, which contributes to water movement in the bodies of water those rivers and streams empty into.

  • Sun: Energy from the sun causes water to evaporate and provides fuel for plants to perform photosynthesis, which is responsible for transpiration.

  • Wind: Wind moves the clouds that transport water through the sky, creates surface waves, contributes to the formation of ocean currents, and facilitates evaporation by moving drier air over water.

  1. Which of the following is the best example of precipitation?

    • (A) clouds

    • (B) fog

    • (C) dew

    • (D) snow

  2. Which of the following is the best example of condensation?

    • (A) rain

    • (B) fog

    • (C) dew

    • (D) sleet

  3. Through which of the following processes does the water cycle remove salt from ocean water?

    • (A) evaporation

    • (B) condensation

    • (C) transpiration

    • (D) perspiration

  4. Which of the following does not power the water cycle?

    • (A) sun

    • (B) moon

    • (C) rocks

    • (D) gravity

Check your answers:

  1. Precipitation is water falling from the sky in liquid or solid form, so Choice (D) is the only correct answer.

  2. Condensation is the product of vapor turning to water, which occurs when dew is formed, Choice (C).

  3. When water evaporates, Choice (A), from the ocean’s surface, the salt is left behind.

  4. The sun, moon, and gravity power the water cycle. Rocks, Choice (C), do not.