Frozen methane bubbles at the surface of Lake Abraham in Alberta, Canada. The methane is released by plants at the bottom of the lake and is trapped as bubbles when it reaches the surface ice.
Jigsaw puzzle subject image credit: Special thanks to Fikret Onal for making the photograph used for this jigsaw puzzle available through the Creative Commons Attribution license. Visit Fikret Onal's Flickr photostream.
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