Residents of the settlement may have built the stone monument to mark the summer solstice.
The rice seeds are duplicates of those stored in a genebank and act as a backup in case of a natural or man-made disaster.
Nutritious and environmentally friendly, seaweed could be the crop of the future in North America, but hopeful growers and marketers of "sea vegetables" face challenges.
The ancient South American Nasca civilization may have caused its own demise by clear-cutting huge swaths of forest, a new study found.
Air pollution in China has cut the amount of light rainfall by 23 percent over the past 50 years.
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