6.3.5: Fossils
Not started yet — this one needs some love.
Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks.
Fossils may form:
when parts of organisms do not decay because decay conditions are absent
when parts of the organism are replaced by minerals as they decay
as preserved traces, such as footprints, burrows and rootlet traces
Many early forms of life were soft-bodied, so they have left few traces behind.
Fossil traces have mainly been destroyed by geological activity.
The fossil record is incomplete, so scientists cannot be certain about how life began on Earth.
Fossils show how much or how little different organisms have changed as life developed on Earth.
Evolutionary tree example: species that share a more recent branch point are more closely related.
Common exam mistakes
Fossils can be remains or preserved traces, not just bones.
Do not only describe how fossils are made; explain how fossils show organisms changing over time.
Soft-bodied organisms often leave few fossil traces, so the fossil record is incomplete.
Geological activity can destroy fossil traces, and older fossils may be buried deep or be hard to find.
Evolution happens across species or populations, not by one fossil organism changing into another during its lifetime.