3.1.15 (HL)—Earth history and evolution

Earth history extends over about 4.5 billion years. Dated fossil layers let us order when forms appear, change and disappear, providing evidence for the evolution of life across geological time.

Compare older and younger strata, but account for preservation and sampling bias. A well-dated appearance or transition is stronger evidence than an absence from the record.

If a shell form occurs in younger layers but not older ones, it may have appeared later—unless older rocks were not preserved or sampled.

Fossilization and sampling are incomplete, so absence may reflect the record rather than true absence.

The fossil record is evidence, not a complete movie of every generation.