Physics and if not its force
It's either 3.5 or 1.2
There would be more evidence spread out through space to be noticed by scientists and it seems like a stretch to go as far back as 4 billion years ago.
(I mean really? That much before the DINOSOURS died? I don't think so)
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Hope this helps
Miri
In order to produce an effective immune response within the body, the person must be injected with a dosage of a virus or bacteria, and for it to be allowed to grow in the person, which replicates just enough to stimulate a response from the immune system.