The origin of life is still cloaked in mystery. There is too little information available to fully test any hypothesis for abiogenesis, let alone determine how quickly or how frequently life may have arisen on the early Earth. All of these changes in living thing were driven by conditions and the addition of life was a contributing factor in those conditions. The very atmosphere we have is the result of the existence of living things.
I don't agree that there is evidence available to allow us to make sound claims about how quickly or how surprising the speed of change (slow or fast) in the evolution subsequent to the appearance of living things is. We know one way that multicellularity could form based on experiments with modern yeast, but this does not tell us about the conditions that multicellularity actually formed under or if it was through the same mechanisms.
I combined into a single timeline one containing some major geological events and one containing biological events with rough times of occurrence based on the evidence to provide a perspective of the occurrence of these events. Keeping in mind that dates are best estimates depending on when the lists were devised and by whom. The list is comprised of major events in the history of the Earth and living things on it.
4600 mya (million years ago) - planet Earth formed.
4500 mya - Earth's core and crust formed.
4400 mya - the Earth's first oceans formed.
3850 mya - the first life appeared on Earth. It was very simple single-celled organisms. Prokaryotes. Exactly how life first arose is a mystery.
3,000 mya - photosynthesis.
2,000 mya - the first complex cells. Eukaryotes.
1500 mya - oxygen began to accumulate in the Earth's atmosphere.
700 mya - the first animals evolved. These were simple single-celled animals.
570 mya - arthropods (ancestors of insects, arachnids and crustaceans).
550 mya - complex animals.
500 mya - fish and proto-amphibians.
475 mya - land plants.
400 mya - insects and seeds.
350 mya - the first land vertebrates evolved. With plants present on the land to provide a food
360 mya - amphibians.
300 mya - reptiles.
225 mya - the first dinosaurs evolved from lizards.
200 mya - mammals.
150 mya - birds.
130 mya - flowers.
65 mya - non-avian dinosaur extinction
2.5 mya - origin of the genus Homo.
200,000-300,000 years ago - appearance of modern humans.
25,000 years ago - Neanderthal extinction.
This list shows a gradual progression of changes, each leading to next steps in that progression. What we do not see are finer details that may have had significant impacts on the rates of change. The origin of mitochondria for instance, would be a critical step in the evolution of eukaryotes, for instance. Or plate tectonics and the impact of that on practically everything. It can also be noted that there is nothing in this to indicate that some more idealized rate should be expected either.
Based on evidence not immediately or at all evident in this list is that some events were dependent on preceding events in order that they take place. The accumulation of an oxygen atmosphere would be a significant event effecting both geochemistry and living things.
I'm not really sure how a particular expectation of rate can be devised from this evidence or that we shouldn't expect it faster due to some condition. In my opinion, you really can't say much for early events. However, for later events the rate does seem to move more rapidly and this is likely the result of established and much more stable natural infrastructure.
