banded iron formation - Rock consisting of alternating light and dark layers of iron-rich chert (hematite and limonite) formed approximately 3,800 million years ago.

bank - The land alongside or sloping down to a river or lake.

amphibole - group of generally dark-colored rock-forming inosilicate minerals, composed of double chain Si O), less mafic than basalt, but more mafic than dacite; rough volcanic equivalent of diorite.

abyssal plain - The ocean floor offshore from the continental margin, usually very flat with a slight slope.

accrete - To add terranes (small land masses or pieces of crust) to another, usually larger, land mass. age - A unit of geological time shorter than an epoch, usually lasting several million years.

alkaline - Term pertaining to a highly basic, as opposed to acidic, substance.

For example, hydroxide or carbonate of sodium or potassium.