Evolutionists take a giant leap of faith when they postulate that life forms in the lower strata changed into the life forms in the next higher layer.
Creationists take an even bigger leap of faith when they say, "God did it".
Unknown to most folks is that there is a 3rd theory of how life came to Earth, and explains the varying life forms over the ages. This one is called the "Intervention Theory". I postulates that those very ealiest life forms were microbes that freed oxygen from the abundant iron oxide on this planet. That each successive generation of life forms used its own particular "talents" to terraform the Earth and make it habitable for the higher forms yet to come. That they did no evolve here, that they were brought here from a source outside of Earth.