earth

Via NPR:

A century ago, miners working in California's Death Valley reported seeing boulders on the desert floor with long trails behind them — as if the stones had been pushed across the sand. But despite 60 years of trying, no one ever saw what moved them.

Now scientists think they've solved the mystery of the "slithering rocks of Death Valley." Using GPS tags pasted to the boulders, and a video camera, a geologist from Scripps Institution of Oceanography and his engineer cousin have evidence that broad, jagged panes of melting ice push the stones across the desert, nudged in one direction or another by the breeze. The team details their results in the current issue of the journal Plos One.

Wrk presented today at the Goldschmidt Geochemistry Conference in Sacramento, California shows that the timing of the giant impact between Earth's ancestor and a planet-sized body occurred around 40 million years after the start of solar system formation. This means that the final stage of Earth's formation is around 60 million years older than previously thought.