Still on shipwrecks, today’s interesting fact has to do with the type of ship that gets sunk. Ships made of metal, with the sole exception of possibly aluminium; do not last as long as wooden ships once they reach the bottom of the sea.

Metal ships corrode in the sea, slowly turning into one metal oxide or another. The oldest metal ships on the seabed are rusting away and may soon only be identified by rust stains on the sea bed. Even these can disappear as metal ions dissolve into the water. As the oceans absorb more carbon dioxide from the air, the sea becomes more acidic and the process will intensify.

In addition, metal ships have different types of metal in them, which sets up electrical currents between different metals and increases the oxidation.

An aluminium shell, with no other metals, will last longer, because when a layer of aluminium oxide forms on the outside of the metal, which then protects the metal underneath, preventing further oxidation. However as most boats made from this material also includes other metals, the resulting electrical current created, will cause some damage from this type of boat.

Wood on the other hand, can last millennia, especially if they get covered by sedimentation. Witness the recent discovery of a Roman boat in Germany, which has been sitting on the sea floor for over 2000 years.

At great depths and in cold environments the dissolution of metal ships may be delayed, but Titanic, sunk deep in cold water, as been shown to be rapidly rusting away.