Type the vocabulary word that completes the blank in the paragraph below.

Below us, our planet is composed of four main layers. The outer surface is called the crust. Beneath that are the (a)   , outer core, and inner core. Circling overhead is a layer of gases that forms our atmosphere. Each layer plays an important part in Earth’s ability to sustain life. For example, plants and animals depend on liquid water on Earth’s surface to drink. As a gas, water can travel on winds to fall on places around the world as rain, snow, or hail

Type the vocabulary word that completes the blank in the paragraph below.

Water on Earth (a)   constantly through the water, or hydrologic, cycle. Liquid water on the planet’s surface is heated by the sun and turns into a gas. This gas, called water vapor, rises into the atmosphere. It gathers into clouds and falls back to the ground as precipitation, such as rain or snow. It collects in bodies of water or soaks into the soil. Then it starts the process over again.

Type the vocabulary word that completes the blank in the paragraph below.

Most areas have (a)   these standard time zones. But there are some exceptions. China crosses three standard time zones. But the country decided to have only one time zone. Some regions divide time zones by half hours. Iran, Newfoundland in Canada, and parts of Australia are examples.

Type the vocabulary word that completes the blank in the paragraph below.

Oceans are one of Earth’s most (a)   resources. But only 5 percent of the ocean floor has been explored. That is changing. The National Oceanic and Atmospheric Administration is studying deepwater canyons off the coast of Virginia. There, they use remote operated vehicles (ROVs) and sonar. Woods Hole Oceanographic Institution uses a human occupied vehicle and other underwater machines to explore and map even deeper waters. These missions help explain Earth’s geologic processes.

Type the vocabulary word that completes the blank in the paragraph below.

Antarctica’s Mount Erebus is one of Earth’s most unusual volcanoes. It is largely covered in ice. But it contains a lake of (a)   hot lava deep inside its crater. Scientists at the McMurdo Station research facility analyze the gas and lava produced by Mount Erebus. The data helps explain how and why volcanoes erupt. It can also tell us a lot about the mantle’s chemical composition.