The evolution of bacteria has progressed over billions of years since the Precambrian time with their first major divergence from the archaeal/eukaryotic lineage roughly 3.2-3.5 billion years ago. This was discovered through gene sequencing of bacterial nucleoids to reconstruct their phylogeny.
The placenta allows nutrients and oxygen travel from the mother to the fetus(or to the Baby. The placenta<span> is </span>fully formed<span> by 18 to 20 weeks </span>These are all I know