task four: 1. which fossil (letter) would be best known as an index fossil? 2. define index fossil 3. why…

Brief Explanations:

1. Without seeing the specific fossils and their characteristics, cannot determine which is an index - fossil. But index fossils are typically widespread, abundant, and existed for a short geological time.
2. An index fossil is a fossil that is used to define and identify geologic periods. It is widespread geographically, abundant in number, and existed for a relatively short period of geologic time.
3. Without information about fossil "D", possible reasons could be that it is not widespread, not abundant, or existed over a long geological time - span, which are not characteristics of index fossils.

Answer:

1. Cannot be determined without more information.
2. A fossil used to define and identify geologic periods, widespread, abundant, and with a short - lived existence in geological time.
3. Lack of information about fossil "D", but it may not meet the criteria of being widespread, abundant, and short - lived in geological time.