Out of all 7 areas, it's #5.
Out of 1, 2, 3, or 4, it's #4.
The index fossils are fossils that are found in the rock strata of certain geologic period, but they are also fossils that are very common and can be found in numerous places around the globe.
Because they can be found all over the globe, and they are indicative of certain geologic period, the geologists have started to use them as a simple way of determining the age of the rock strata. While this method can not provide the geologists with an accurate year for the formation of the rocks, it is still able to determine the relative age of the rocks. By determining the relative age with such ease by using the index fossils, the geologists are able to immediately make conclusions about the rock strata, have basic information about it, and largely be aware of the processes that formed them and influenced them.
A major difference between formal and informal economic sectors is that a formal economy is composed of an organized group of people working in the same environment and who are legally and socially aware about their rights and have a formal contract with the employer
An informal economy is composed of people who are not necessarily organized, have no social security cover of any kind and have poor knowledge about the need to protect themselves socially and economically and have no formal contract with the employer.
Miscegenation. Hope this helps:)
