1. Cooled lava formed many ___.
a) cities b) islands c) continents
2. Molten rock deep below the Earth’s crust is called ___.
a) enigma b) sigma c) magma
3. Volcanic explosion is called ___.
a) corruption b) eruption c) extrusion
Text 7. What do we know about the surface of Mars?
Ever since the first successful flyby over Mars in 1964, scientists have been striving to gather more and more information about our rusty-red planetary neighbor. What we know already, based on soil and rock samples, as well as our observation of the planet, is that Mars is dusty, dry and cold. Its surface is heavily dotted with deep craters in some areas, while other areas have volcanic mountains even higher than Earth’s highest volcano. Mars also has low-lying plains where scientists have discovered evidence of wind streaks, dunes and basins that resemble riverbeds. There are canyons on Mars, far deeper than our canyons on Earth, as well as polar regions – icy caps made up mostly of frozen carbon dioxide. Evidence suggests that liquid water once flowed over the surface of Mars. But as far as we know today, Mars remains a dry, rocky planet pummeled by dust storms and pocked with crater cavities.