Fossils
Preserved remains or traces of ancient organisms found in rock
What are fossils?
The principle stating that deeper rock layers are older than shallower ones
What is the principle of superposition?
The general pattern of life seen from older to younger rocks
What is simple organisms appearing before complex ones?
The major animal group trilobites belong to
What are arthropods?
Evolutionary change occurring within a single species over time
What is evolution within a lineage?
The type of environment where fossilization is most likely to occur
What is water (oceans, lakes, or rivers)?
The type of rock that fossils are found in
What are sedimentary rocks?
Evidence that species change gradually over time
What is gradual evolutionary change?
Why trilobites fossilize so well
What is because they had hard exoskeletons?
When one species divides into two descendant species
What is lineage splitting (speciation)?
Why the fossil record contains mostly hard parts like shells and bones
What is because soft parts rarely fossilize?
Why fossils cannot be directly dated with radioactive isotopes
What is because radioactive isotopes occur in igneous rocks, not sediments?
Fossils showing mixtures of traits from earlier and later groups
What are transitional fossils?
The specific trilobite feature used to track evolutionary change
What are pygidial ribs?
Fossil evidence showing multiple descendant species from a common ancestor
What is branching descent from common ancestors?
One reason the fossil record is incomplete
What is erosion, destruction of rocks, or rare conditions for fossilization?
How scientists determine fossil ages using nearby rocks
What is bracketing fossils with dated igneous layers?
Why fossils in nearby layers tend to resemble each other
What is because later species descend from earlier ones?
What happens to trilobite traits over millions of years
What is gradual change in traits over time?
Why different lineages do not always evolve in the same way
What is differing environmental pressures?
The estimated fraction of all species that ever lived that we have fossils for
What is about 0.1–1 percent?
What finding would disprove evolution, according to the chapter
What are fossil rabbits in the Precambrian?
Why fossils appear in a specific order rather than randomly
What is common ancestry and descent with modification?
What trilobites show about how evolution proceeds
What is that evolution occurs within multiple lineages?
What the fossil record shows instead of species appearing unchanged
What is that species evolve and split rather than remaining unchanged?