The Golden Spikes: The Index Fossils Quiz

If an organism lived for millions of years across many eras, then it doesn't help narrow down a specific time; if it lived for a short, distinct period, then finding it in a rock layer pinpointed that specific time; therefore, a short lifespan is required.

If Fossil X only lived during a specific slice of time, and if it is found in both locations, then both layers must have been deposited during that same slice of time regardless of the rock type.

If an organism lived everywhere but for a very long time, it's not specific; if it lived for a short time but only in one pond, it's not useful globally; if it meets both A and B, then it is a perfect tool for dating rocks.

If trilobites were abundant globally and their body shapes changed rapidly over short geological periods, then they provide clear "markers" for different parts of the Paleozoic; therefore, they fit the index fossil criteria.

If correlation requires finding the "same" markers in different places, and if B and C appear in both the New York and France layers, then B and C are the shared evidence used to link the two locations.

If most organisms are rare, or lived for too long, or didn't have hard parts to fossilize, then they fail the requirements; if only a small percentage of species meet all the strict criteria, then most organisms are not index fossils.

If different regions have different rock sequences, and if index fossils allow us to match the ages of those sequences, then we can piece together a single, global timeline of Earth's history.

If the fossil only existed during a specific window of 5 million years, and if that fossil is physically part of the rock, then the rock must have formed during that exact window of time.

If a fossil is found in North America, Europe, and Asia, then it has a wide distribution; if it is found globally, then scientists can use it to match rock layers across different continents; therefore, wide distribution means living in many places.

If a fossil looks exactly like ten other species from different time periods, then it cannot be used to identify a specific age; if it is easy to identify, then geologists can use it reliably; therefore, distinct features are necessary.

If index fossils tell us which layer is older or younger than another based on the fossil's known lifespan, then they are providing a comparison; if it is a comparison rather than a specific number of years, then it is relative age.

If an index fossil must represent a narrow "snapshot" in time, and if an organism lived for 500 million years, then finding it doesn't tell you which specific period the rock is from; therefore, it is a poor index fossil.

If an index fossil only exists during a specific time, and if that organism goes extinct, then no rock layers formed after that date can contain that fossil; therefore, the extinction defines the end of that fossil's "zone."

If fossils are formed when organisms are buried in sediment, and if lava is hot enough to melt or destroy organic remains, then fossils are almost never found in igneous rock; therefore, index fossils cannot be used to date them directly.

If scientists use a specific fossil to identify a section of the geologic column, and if that fossil defines the boundaries of that section, then that specific rock interval is called a biozone.

If the geologic time scale is a hierarchy, and if Eras are divided into smaller, more specific units, then those units are called Periods.

If it's only in one cave, it can't correlate other areas; if it looks like older species, it's not a clear time marker; therefore, A and B make it a bad index fossil.

If a geologist finds the same index fossil in two different states, then they can conclude those layers formed at the same time; if they are matching these layers based on evidence, then the technical term for this matching process is correlation.

If the ammonite layer was deposited first, and if the Law of Superposition states newer layers sit on top, then any layer above the ammonite layer must be younger.

If marine plankton float in currents worldwide and have hard parts that fossilize easily, then they will be found in many places; if they are common, then they are easy to find; therefore, they are the best candidates.