It acts as a sunlight filter, shielding life on Earth from harmful ultraviolet rays that put humans at greater risk of skin cancer and cataracts and harm marine life, the agency said.

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Some scientists, giving their imaginations free rein (and extrapolating from Earth's own sea creatures), have suggested filter-feeders, such as whales.

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Like the astronauts aboard Apollo 13 who had to build a CO2 filter from whatever was available in their capsule under the direction of engineers back on Earth, we are forced to innovate in real time.

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