Just how hard is it to find a plane at the bottom of the ocean?
Imagine standing on a mountain top and trying to spot a suitcase onthe ground below. Then imagine doing it in complete darkness.
That's basically what crews searching for Malaysia Airlines Flight 370 have been trying to do for a month.
Thursday is Day 34 in the search for the plane that disappeared March 8, taking with it 239 passengers and crew members.
Officials believe the Boeing 777, while en route from Kuala Lumpur, Malaysia, to Beijing, crashed in the southern Indian Ocean.
Pinning their hopes on signals they think came from the plane's black boxes, they narrowed the focus of their search Thursday to a 22,400-square-mile (58,000-square-kilometer) area -- about 45 times the size of Los Angeles.
But the real challenge is the depth of the water they're dealing with.
The signals that were detected Saturday, and again Tuesday, came from the ocean floor 15,000 feet below the surface. That's 2.8 miles (4.5 kilometers).
That's deeper than an inverted Statue of Liberty (305 feet), deeper than an inverted Eiffel Tower (1,063 feet), deeper even than an inverted Burj Khalifa, the tallest building in the world (2,717 feet).
In fact, if you stacked the Burj end-to-end five times, it would reach only 14,000 feet -- still not deep enough to reach the spot searchers believe the pings are coming from.
At these depths, marine life is unlike anything most people have ever seen.
"The deeper you go you find less and less," marine biologist Paula Carlson said. "They have to be very cold tolerant, they might not even have eyes. They may be blind, because they don't need to see, there's no light down there."
The pressure at nearly 15,000 feet is crushing -- so much so that very few manned submarines can withstand it.
"There are only about half a dozen subs that can go to half the ocean depth with a number of countries having that capability," said Sylvia Earle, an oceanographer for National Geographic. "If it gets to the point of collapse, it basically implodes, it just crushes."
Only a handful of people have traveled to such staggering depths. One of them is movie director James Cameron, who using a state-of-the-art vessel, dropped 35,000 feet, or about 7 miles, to the deepest place on Earth -- the Challenger Deep in the western Pacific Ocean.