Which Finding Was Not Known to Nineteenth-Century Geologists

Which finding was not known to nineteenth-century geologists?

A) Fossil organisms found in more recent strata resemble modern organisms more than those found in more ancient strata.
B) Fossils of similar organisms are found in widely separated places on Earth.
C) Radioactivity can be used to determine the age of rocks.
D) Certain fossils are always found in younger strata,and certain other fossils are always found in older strata.
E) Nineteenth-century geologists knew all of these findings.