Understanding the Elements of the Periodic Table - OXYGEN

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On August 20 and again on September 9, 1975, scientists at the National Aeronautics and Space Administration (NASA) launched two unmanned spacecraft named Viking 1 and Viking 2 into outer space. Their mission was to search for signs of life on Mars. After a ten-month journey, the two spacecraft entered into orbit around Mars and released landers that touched down on July 20 and September 3, 1976. Viking 1 landed at the Chryse Planitia, a rolling, boulder-strewn plain with scattered dusty dunes and outcrops of bedrock. These rocks are believed to be worn-away remnants of colcanic rock from billions of years ago. Viking 2 landed at the Utopia Planitia, a similar volacnic plain nearly 4,000 miles (6,500 kilometers) away, with shallow troughs that may have been caused by sheets of ice expanding and receding across the Martian surface. Both of these landers transmitted hundreds of measurements and colour photographs back to Earth. Several of their scientific experiments were designed to discover whether there were bacteria living in the soil and to find evidence of oxygen, an essential element for life.