Most fossils on Earth are in fact very very tiny. So tiny you can't see them without a microscope. Diatomaceous earth is an example of fossil remains we grind up and use for various purposes of our own. Rocks like slate, chert, radiolarite, stromatolites etc. were formed predominantly by microorganisms. Modern scientists use a nanometers fine sieve or centrifugal separation to analyze these fossils, usually through SEM.
Some of these microfossils, typically from earlier periods, bear little resemblance to any modern form of life on earth.