The answer is different magnification lenses. Leeuwenhoek use a microscope with different magnification lenses which enabled him to see bacteria. <span>His microscope was able to achieve 50-300x magnification, which enabled him to see a variety of bacteria.</span>
Their purpose is reproduction.
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)
◕‿◕
Hope this helps
Miri