JUDY WOODRUFF:

But first: Researchers have been watching for months, waiting for a huge iceberg to break away from an ice shelf in Antarctica. That break was confirmed today.

And just to give you a sense of the size, the volume of the iceberg is said to be twice as large as Lake Erie.

Miles O'Brien has been watching all this and digging into the larger questions about the ice shelf.

Here's an update to an earlier report. It's part of our weekly segment on the Leading Edge of science.