The standard approach to looking at fossils in the geological column is to assume that lower is older.Since the geologic column represents millions of years of Earth's history, then obviously the fossils in each of the layers must be the same age as the layer in which they are found.
It goes against human nature to challenge long held ideas of truth.
What is especially interesting is that the fossils do appear to show a progression from the most "simple" of organisms, such as single celled creatures like bacteria, to the most "complex" organisms, such as vertebrates, mammals, and of course humans.
This evolutionary progression seems to be clearly demonstrated in that certain kinds of creatures in the upper layers are rarely if ever seen in lower layers.
Since each of these layers seems so specialized it is easy to conclude that one type of creature gave rise to the next type of creature over the course of whatever time it took to form the various layers between them.
Radiometric dating and many other techniques are used to support the idea that this transformation process took tens and hundreds of millions of years.