Absolutely, when DNA is available: scientists can look at the DNA, locate the differences, and list the changes that had to have happened to get from one to the other, because the ways in which DNA can change are known. At that level, evolutionary change is a great deal like geological change; just as an example, the phrase “this sequence is inverted” is something that can be said of DNA and of rock strata. In short, evolutionary change is just chemistry with known building blocks.
Whereas for gravity scientists don’t even know what it is: is it a force where particles – gravitons – are exchanged between physical bodies? is it a bending of spacetime? does it behave the same over vast distances, e.g. hundreds of thousands or millions of light years? does it have a dual nature, like light which acts like a wave or a particle depending on circumstances?
We know the building blocks of the stuff that has to change for evolution to happen; we don’t know the building blocks of gravity.
There is no “suddenly” about it; the Cambrian lasted some fifty million years.
And “numerous novel phyla” is a misunderstanding based on miscomprehension of how the biological classification system works. Here’s a darned good piece on how that works:
Though you’ve got things backwards: the “orchard of life” position has been made less and less likely as more and more evidence accumulates.