Which is the first step that geologists must do to compare rock layers at distant locations? O find the absolute age of rocks at both locations
O compare a layer at one location to layers at other locations
o identify index fossils in one or more layers at one location
O collect fossils from different locations to study the organisms' lifestyles

Ordering of Rock Layers

Scientists read the rock layers knowing that each layer is deposited on top of other layers.

The law of superposition states that each rock layer is older than the one above it.  So, the relative age of the rock or fossil in the rock or fossil in the rock is older if it is farther down in the rock layers.

Relative dating can be used only when the rock layers have been preserved in their original sequence.

Index Fossils

Certain fossils, called index fossils, can be used to help find the relative age of rock layers.  To be an index fossil -

an organism must have lived only during a short part of Earth's history;

many fossils of the organisms must be found in rock layers;

the fossil must be found over a wide area of Earth;

the organism must be unique.

The shorter time period a species lived, the better an index it is.

Fossils that are found in many rock layers, therefore living long periods of time, do not qualify as independent

Explanation: :) ;)

the answer is d. chordata