After about 85% of the current Earth history had been “caulked up”, oxygen concentrations finally became high enough and there was sufficient accumulation of organic nutrients that the angels could develop and introduce multicellular organisms into the environment. A large variety of simple, experimental animals, called the Ediacarian fauna, was placed into marine environments during the Cambrian period, about 600 million years ago. This is the period that paleontologists call the Cambrian explosion. A vast array of invertebrates were developed and introduced into the environment. Some looked a bit like Cnidarians (jellyfish, sea anemones and the like); others resembled annelids (earthworms). Primitive examples of all existing phyla (the second highest taxonomic category) of animals were developed during the Cambrian Period.
The animals of the Burgess shale are an example of Cambrian animal fossils. These fossils, from Canada, show a bizarre array of creatures, some that appear to have had unique body plans unlike those seen in any living animals.
Although examples of all the phyla of animals were produced at this time, these were not the modern forms we see today. Most were invertebrates, and vertebrates (such as mammals, reptiles, birds, amphibians and fish) were represented by a small, sliver-like thing called Pikaia. Plants were not yet present and the dry land was still uninhabited.
I believe the creation angels were experimenting and learning how to build larger, more complex organisms. After the science and art of creating single-celled organisms had been fully mastered, the angels were faced with the next two levels in building a sophisticate organism:
1. Cellular differentiation - While the creation of single-celled organisms required elegant molecular construction techniques using macromolecules and membranes, with multi-celled creatures came the really daunting task of learning how to make cells differentiate into different tissues.
2. Programming instinctual behaviors - They also had to create a central nervous system and “construct” programs to guide behavior and allow the animal to learn from the interaction with the environment in some kind of molecular language.
Simple multicellular organisms could replicate via binary fission or budding, but along with the introduction of cellular differentiation, another means of replication was required. They created a new cell type, the zygote egg. This egg contained a single celled zygote and the required nutrients to allow the zygote to differentiate and grow into an immature organism and this was all protected by some kind of shell. The angels made zygote eggs as needed to introduce new species; they had to make two, one male and one female, for each new species.