Why are fossils found in the deepest rock layers generally simpler than those found in upper layers?
ABecause simple organisms are heavier and sink deeper
BBecause deeper layers are older, and life started simple and became more complex over time through evolution
CBecause complex organisms dissolve faster in rock
DBecause scientists arrange them that way for display
In undisturbed rock, the deepest layers were deposited first and are the oldest. Since life on Earth began with simple, single-celled organisms and became more complex over billions of years through evolution, the oldest layers contain the simplest fossils and newer layers contain more complex ones. This pattern is consistent worldwide and is one of the strongest pieces of evidence for evolution.
Question 2 True / False
Nearly every organism that has ever lived left behind a fossil.
TTrue
FFalse
Answer: False
Fossilization is extremely rare. It requires specific conditions: the organism must be buried quickly in sediment before it decomposes, and minerals must gradually replace its hard parts. Most organisms decompose completely without leaving any trace. Scientists estimate that fossils represent less than 1% of all species that have ever existed.
Question 3 Short Answer
What is a transitional fossil, and why is it important as evidence for evolution?
Think about your answer, then reveal below.
Model answer: A transitional fossil shows features of both an ancestral group and a descendant group. For example, Tiktaalik is a fossil that has features of both fish (scales, fins) and land-dwelling amphibians (flat head, primitive wrist bones). Transitional fossils are important because they provide direct evidence that one group of organisms evolved into another over time.
Transitional fossils fill in the 'gaps' between major groups of organisms, showing the intermediate steps of evolution. They demonstrate that evolutionary change happens gradually rather than in sudden jumps, with organisms displaying mixtures of old and new features.