Banging noises detected underwater Tuesday and Wednesday in the massive search area have provided hope for survivors – but it’s like finding a needle in a haystack, and time is of the essence, experts say. Meanwhile, the crew would have “limited rations” of food and water in the 21-foot submersible, which has rudimentary controls and no room for passengers to stretch out, officials have said.

“We need a miracle,” oceanographer and water search expert David Gallo told CNN on Wednesday. “But miracles do happen.”

[As one rescuer told a reporter, never underestimate the will to live. But even that is subject to the hard science of biology. If they can get rescued in the next hour, maybe there will be enough margin to matter, but at least from media reports this morning, they’re still not sure where it is. — Ed]