Proterozoic eucaryotes from eastern california.

Both procaryotic and eucaryotic nannofossils occur in chert from the upper Beck Spring Dolomite (Pahrump Group) in northeastern San Bernardino County, California. These fossils include the oldest reasonably certain records to date of chlorophycean and chrysophycean algae, and hence of the eucaryotic or mitosing cell. Associated with these are cyanophycean procaryotes of still more ancient affinities. Indirect radiometric evidence implies an age of 1.2 to 1.4 aeons (1.2 to 1.4 x 10(9) years) for the enclosing rocks. Associated stromatolites are consistent with such an age assignment.