Labels: text | screenshot OCR: MARS AND EARTH: A COMPARATIVE HISTORY THE SEARCH FOR LIFE Inside the planets The rocks within the planets were radioactive. And like all radioactive bodies, they generated heat. A kilo of pure uranium, for example, can produce as much energy as almost three million metric tons of coal. And the more radioactive material contained in the rock, the greater the heat produced. Although the heat tended to disperse toward the planets' outer layers, rock conducts heat very slowly, and the heat built up in the core. Volcanic activity on Earth As the temperature of the core rose, the rocks began to melt. The lightest materials were simply vaporized. Meanwhile, the internal pressure climbed, until eventually molten rock-lava-and gases spewed through openings in the crust. MARS BETAT
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