What is the main problem with comparing the tree of life with the fossil record?

Darwin gave the concept in evolution of species.

Explanation:

As we know the tree of life is quite massive and comparing it needs to be understood well in terms of fossils that were once hidden inside the layers of earth rock masses. The tree is phylogenetic representing the unique ancestral history of every creature. Analyzing their morphological, behavioral and habitats are mostly evaluated in the tree of life  One major challenge is to find the roots of life for the evolutionists. Finding out the nature of the last common ancestor. Some theories suggest that the same ancestor has the same common history of origin may lead to confusion of evolutionist as acing them becomes difficult.