The Cambrian and Precambrian life appear suddenly

Wrong.

[quote]... But over the past several years, discoveries have begun to yield some tantalizing clues about the end of the Ediacaran. Evidence gathered from the Namibian reefs and other sites suggests that earlier theories were overly simplistic — that the Cambrian explosion actually emerged out of a complex interplay between small environmental changes that triggered major evolutionary developments.

Some scientists now think that a small, perhaps temporary, increase in oxygen suddenly crossed an ecological threshold, enabling the emergence of predators. The rise of carnivory would have set off an evolutionary arms race that led to the burst of complex body types and behaviours that fill the oceans today. “This is the most significant event in Earth evolution,” says Guy Narbonne, a palaeobiologist at Queen's University in Kingston, Canada. “The advent of pervasive carnivory, made possible by oxygenation, is likely to have been a major trigger.” [/quote]

But wait! There's more!!
[quote] Sperling has looked for insights into Ediacaran oceans by studying oxygen-depleted regions in modern seas around the globe. He suggests that biologists have conventionally taken the wrong approach to thinking about how oxygen shaped animal evolution. By pooling and analysing previously published data with some of his own, he found that tiny worms survive in areas of the sea floor where oxygen levels are incredibly low — less than 0.5% of average global sea-surface concentrations. Food webs in these oxygen-poor environments are simple, and the animals feed directly on microbes. In places where sea-floor oxygen levels are a bit higher — about 0.5–3% of concentrations at the sea surface — animals are more abundant but their food webs remain limited: the animals still feed on microbes rather than on each other. But around somewhere between 3% and 10% oxygen levels, predators emerge and start to consume other animals.

The implications of this finding for evolution are profound, Sperling says.The modest oxygen rise that he thinks may have occurred just before the Cambrian would have been enough to trigger a big change. “If oxygen levels were 3% and they rose past that 10% threshold, that would have had a huge influence on early animal evolution,” he says. “There's just so much in animal ecology, lifestyle and body size that seems to change so dramatically through those levels.”

The gradual emergence of predators, driven by a small rise in oxygen, would have meant trouble for Ediacaran animals that lacked obvious defences. “You're looking at soft-bodied, mostly immobile forms that probably lived their lives by absorbing nutrients through their skin,” says Narbonne.

. . .

The rise of predation at this time put large, sedentary Ediacaran animals at a big disadvantage. “Sitting around doing nothing becomes a liability,” says Narbonne.

The moment of transition from the Ediacaran to the Cambrian world is recorded in a series of stone outcrops rounded by ancient glaciers on the south edge of Newfoundland. Below that boundary are impressions left by quilted Ediacaran animals, the last such fossils recorded on Earth. And just 1.2 meters above them, the grey siltstone holds trails of scratch marks, thought to have been made by animals with exoskeletons, walking on jointed legs — the earliest evidence of arthropods in Earth's history.

No one knows how much time passed in that intervening rock — maybe as little as a few centuries or millennia, says Narbonne. But during that short span, the soft-bodied, stationary Ediacaran fauna suddenly disappeared, driven to extinction by predators, he suggests.

Narbonne has closely studied the few fauna that survived this transition, and his findings suggest that some of them had acquired new, more complex types of behaviour. The best clues come from traces left by peaceful, wormlike animals that grazed on the microbial mat. Early trails from about 555 million years ago meander and criss-cross haphazardly, indicating a poorly developed nervous system that was unable to sense or react to other grazers nearby — let alone predators. But at the end of the Ediacaran and into the early Cambrian, the trails become more sophisticated: creatures carved tighter turns and ploughed closely spaced, parallel lines through the sediments. In some cases, a curvy feeding trail abruptly transitions into a straight line, which Narbonne interprets as potential evidence of the grazer evading a predator. [/quote]

There are many more details regarding the changes from the Ediacaran to the Cambrian era. But the overall point is that your claim, "without any evidence of evolution," is dead wrong. There's a wealth of evidence about the transition that led to the Cambrian "explosion."