The tidal forces on the Earth due to _____ only 0.46 of those due to the Moon.

Most radioactive elements occur in igneous and metamorphic _____ fossils occur in sedimentary rocks.

_____ radioisotope is encountered, the first step in its identification is the determination of its half-life.

The Missouri _____ longest river in the United States, flows through seven states from its source in Montana to its confluence with the Mississippi.

Coral islands such as the Maldives are the tips of reefs built during periods of warm climate, when _____ higher.

Hail forms within large, dense cumulonimbus _____ develop on hot, humid summer days.

Measles is a highly contagious viral disease _____ by a characteristic skin rash.

Charles Darwin's first scientific book, published in 1842, _____ a since substantiated theory on the origin of coral reefs and atolls.

Phytoplanktons thrive where _____ phosphorus into the upper layers of a body of water.

By the end of 1609, Galileo had a 20-power telescope that enabled him to see _____ planets revolving around Jupiter.

On every continent except Antarctica _____ more than 30,000 species of spiders.

Many bugs possess defensive scent glands and emit disagreeable odors when _____.

Hurricanes move with the large-scale wind currents _____ are imbedded.

_____ the Earth's ice to melt, the Earth's oceans would rise by about two hundred feet.