1. what is the age of the hypothetical rock layer that these fossils were collected from?

2. based on the age determined, do you think that this group of fossils could be considered index fossils? why or why not?

3. suppose that the particular trilobite listed in line 7 of the data table is limited to rock of lower devonian age and that these trilobite fossils are widespread throughout north america. can these fossils be considered an index fossil? why or why not?

4. the fossils in this group were collected from limestone and shale rocks. based on what you have learned about the formation of these rock types, what type of environment did these organisms live in?

5. shale often contains fossils of leaves. if the gastropods listed in line 3 and line 6 were collected from shale containing leaf fossils, could you use radiocarbon dating to assign a numerical date to this rock unit? explain.

1. Judging by the occurrence of the of the fossils they are all found in a rock layer from the Devonian era. Some of the fossils occurred even earlier than the Devonian era, but all of them are present in the Devonian era, which gives us the previously stated conclusion. 

2. index fossils are fossils that come from a species that were most widespread in that geological era. In the Devonian, the dominant group of animals was the trilobites, brachiopods, and corals, so this group of fossils would be excellent index fossils.

3. As previously said, a good fossil index species is one that is widespread and specific for a rock layer, so the trilobite marked with number seven would not make a great index fossil. Fossils that are not widespread are referred to as zone fossils,

4.Shale rocks are formed by depositions of sediments in water covered soil which indicates that some of these organisms have lived in swamps, river deltas or lagunes Limestone is formed by deposition of the skeletal elements of marine animals like corals, so this indicates that some of the animals may have lived in  reefs similar to today's coral reefs, consisted of algae and corals.

5. Since we have determined that these fossils are from the Devonian era, it would be impossible to date this rock with radiocarbon method. The radiocarbon method can only measure levels of carbon isotopes that are not older than 50,000 years and the Devonian era was around 400 million years ago.

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