Sulfate-reducing microorganisms are responsible for the sulfurous odors of salt marshes and mud flats. Much of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides. These metal sulfides, such as ferrous sulfide (FeS), are insoluble and often black or brown, leading to the dark color of sludge.
The largest aircraft used for a scheduled domestic service in the USA that is a DOMESTIC route only, is the Boeing 777, though the most common is a Boeing 757 and 767. Some airlines use larger aircraft on domestic legs on an international flight throughout the USA, which do include the 747, however some airlines don't have a license to carry domestic passengers on those routes.
The present Air Force One aircraft, which first flew under then US president George H W Bush in 1990, were commissioned by Ronald Reagan. Currently, there are only 20 models of Boeing 747-200 jumbo jets, which mostly carry cargo in the developed world. People sometimes ask me what the biggest perk of being president is, US President Barack Obama told visitors at the White House last week.