What the search for Flight 370 has found (that's not the plane)

(CNN)Search teams have been looking for the wreckage of Malaysia Airlines Flight 370 for nearly two years, and thus far, boats dragging high-tech detection equipment across the Indian Ocean and teams searching from the skies have had little success.

This week, hopes of finding out what happened to the plane were renewed when an American tourist found a piece of plane debris off the coast of Mozambique. The debris appeared to be from a Boeing 777, like the missing MH370 airliner, according to a U.S. official. But Cmdr. Joao Abreu, the chief executive of the Mozambique Civil Aviation Authority, told CNN's David McKenzie that the piece of debris might belong to a "medium-sized plane" and not a 777.
Authorities from Australia and Malaysia have urged caution before jumping to conclusions, and the debris is on its way to Australia for further examination.
    Until now, the closest searchers have come to finding the whereabouts of the missing plane came on July 29 when airplane debris was found on the shores of a French island in the Indian Ocean. It was wreckage from a Boeing 777 -- the same type of aircraft as MH370. In September, French investigators confirmed it: The wing part found on Reunion Island was from the plane that disappeared with 239 people on board in March 2014, en route from Kuala Lumpur, Malaysia, to Beijing.
    The find created hope that the rest of the plane would soon be located, but months passed with no major developments.
    As search crews return to the seas after a break, here's a look at some of things items they've found in the past two years:

    Old Ironsides

    In December 2015, a team found a 200-year-old shipwreck while searching for Flight 370.
    "An anomalous sonar contact was identified in the course of the underwater search, with analysis suggesting the object was likely to be man-made, probably a shipwreck," said the Joint Agency Coordination Centre, the Australian Transport Safety Bureau agency directing the search.
    In January, searchers sent out a ship called Havila Harmony to take a picture using the sonar on board an autonomous underwater vehicle, the agency said.
    They showed the image to experts at the Shipwreck Galleries of the Western Australian Museum, who said the wreckage is probably a ship made of steel or iron from the early 19th century.
    As surprising as the find may seem, it wasn't the first shipwreck the searchers found in the search zone.
    Search vessel Fugro Equator's deep tow system "detected a cluster of small sonar contacts" of potential interest near the so-called 7th arc. Pictures revealed startlingly clear images of a previously uncharted wreck, also most likely from the 19th century, according to Australian authorities. An anchor, as well as parts of a destroyed hull, were clearly seen in the photos of the wreck 3,900 meters (12,795 feet) deep.
    Some of the shipwreck's shinier debris initially piqued searchers' interest as possibly being pieces of MH370. But the plane still eluded them.
    MH370 searchers find uncharted shipwreck
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    Seen today, gone tomorrow

    On March 24, 2014, the same day Malaysian Prime Minister Najib Razak broke the news to anguished families of MH370 passengers that new data suggested the flight ended in the southern Indian Ocean, searchers thought they had a clue as to just where to find it.
    Australian officials said they had spotted two objects in the southern Indian Ocean that could be related to the flight.
    One object was "a gray or green circular object," and the other was "an orange rectangular object," the Australian Maritime Safety Authority said at the time.
    Mary Schiavo, a CNN aviation analyst and former inspector general for the U.S. Department of Transportation, said gray/green is the color of the inside of the aircraft and that metal and other things in the aircraft are of gray/green color, everything from the metal in the fuselage and pieces of the mechanical parts, while orange and bright yellow are the color of the emergency escape slides and life rafts inside the plane.
    But the Australian naval ship HMAS Success didn't turn up the objects when it searched and a U.S. surveillance plane sent to follow up was unable to find the objects, which had been the latest in a series of sightings, including "suspicious objects" reported by a Chinese military plane. Ten aircraft -- from Australia, China, the United States and Japan -- searched the area.
    Days before, on March 22, a civilian aircraft reported seeing a wooden pallet as well as strapping belts, Australian authorities said. While wooden pallets were among the items on Flight 370, such pallets are common in the ocean shipping industry, so they may be unrelated.
    A Royal New Zealand Air Force P-3 Orion was sent to the area, but only reported seeing bunches of seaweed, according to Australian authorities.

    Pings & things

    On April 5 and 8 of 2014, hopes were raised again when signals believed to be from the missing aircraft's data recorders -- so-called black boxes -- were detected near an arc where an Inmarsat satellite had last communicated with the plane.
    These signals, or pings, turned out to be another false lead, when on May 28 a U.S. Navy official told CNN that authorities had come to believe the pings did not come from the onboard data or cockpit voice recorders but instead came from some other man-made source unrelated to the jetliner.

    Unexplored ocean floor

    It's not just shipwreck parts and pieces and pings searchers in the area have found.
    As ships surveyed tens of thousands of square miles of the bottom of the ocean where the plane is believed to have gone down, Australian searchers reported extinct volcanoes, immense ridges and cavernous trenches discovered on the seabed by experts mapping the underwater terrain with state-of-the-art equipment.
    The depth and seafloor terrain of this area of ocean was largely unknown before the search for the plane drew attention to it.

    What's next?

    According to the latest operational search update from the Australian Transport Safety Bureau's Joint Agency Coordination Centre issued March 2, more than 85,000 square kilometers (3,2818.68 square miles) of the seafloor have been searched so far. As agreed to in April 2015, 120,000 square kilometers will ultimately be thoroughly searched. It is anticipated this will be completed around the middle of the year, according to the update.
    The ships Fugro Equator and Havila Harmony continue to conduct various underwater search operations. The ship Fugro Discovery arrived back in the search area on February 25 to join them.
    If search teams find the plane, Australia, Malaysia and the People's Republic of China have agreed to plans for recovery activities, including securing all the evidence necessary for the accident investigation. If no credible new information is found in the current search area, the governments involved have agreed that there will be no further expansion of the search.