Which phrases describe organisms that formed index fossils? check all that apply. are extinct had hard parts were generally large were alive only for a short time lived in a narrow geographic area

are extinct

were alive only for a short time

lived in a narrow geographic area

had hard parts

Options (1), (2), and (4)

Explanation:

Index fossils are usually defined as those fossils that were present on earth for a very short period of time. They were very broadly distributed in almost all parts of the world. They were comparatively smaller in size and comprised of hard parts that were preserved under favorable conditions which are found at many places in the present. These are extinct species. For example, trilobites and ammonites.

These index fossils are very useful because it helps in determining the age of the fossils as well as rocks by applying the radioactive dating method.

thus, the correct answers are options (1), (2), and (4).

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.

i would say it is