With a nod to Arbor Day, here's a rundown of some of the Earth's biggest tree species -- and what ails them.
The hottest party in Montreal this winter is also the coldest.
Here are some spots on the planet where humans have really dug in.
A visionary couple and an ever-growing army of volunteers work to return 2 million acres in South America back to nature.
The Geological Society of London just released the winners of its '100 Great Geosites' photo contest of geological wonders in the U.K. and Ireland.
Smoke from wildfires billows over Crater Lake, Arctic sea ice isn't up to years past and fall colors pop in Siberia.
See some of the most spectacular waterfalls from around the world.
Some of the oddest sites on our planet are below the surface.
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