When you start breaking down life, you finally reach the fact that life is a carbon-based lifeform. It’s not difficult to think of life diversifying from a common carbon-based ancestry. What else is it going to do? Life changes due to environment and other things, so what’s so hard to understand about our common carbon-based existence changing and diversifying. Now if things went the other way where everything was extremely complex and made good use of their surroundings, but changed to be extremely simplistic to the point they border on the definition of life, then that would seem wrong.
As far as all this fossil jazz goes, I’ve mentioned this several times, but it just goes in one ear and out the other: A huge portion of the earth is constantly renewing itself. The earth’s crust is made up of about 12 major plates that are constantly in motion. These huge slabs collide at places and one will dip below the other and go into the mantle and melt. At the same time, plates are rising up out of the mantle. Fossils aren’t going to survive this molten trip. Add to that volcanic eruptions, meteor dust, etc. that blankets the earth, covering up stuff. Erosion, freezing and thawing, glacier activity, floods, plants and animals….. they all do their part in erasing the fossil record.
Even with all that going on, we still have fossils to work with and study. But how many fossils have we found of man with t-rex bite marks through his skull? How many dinosaurs left hooked claws broken off and embedded in human fossil remains? None. None because dinosaurs and man did not live at the same time.