Protists Are Almost It Until About Precambrian Times...
Then we see the protists are really sort of it until almost the Precambrian period. I know that this is very recent and multicelluar animals may have arisen much earlier. But even if they did, at least according to the fossil record they were fairly insignificant. So if you start to look at the fossil record of life from about 3.5 or so billion years ago, up until the Cambrian boundary, this was, to a large extent, the age of microbes - protists and this was not an insignificant a period of time. Then you get to the Cambrian boundary and you quickly have animals and plants and dinosaurs squeezed in here, and birds and of course the dinosaurs.
Modern analogs...
So you can see, protists were not insignificant players here in evolutionary history. I said I'd mention a little bit about modern analogs. I show these slides partly because every time I see them, I myself am impressed. Here are stromatolites in the Precambrian. You can see these striations, stripes going across. Here is a modern microbial mat. This is one that I've done some work on in Baja, California. This was in a salt pond that has salinity roughly three times that of the ocean, which is 35 parts of 1,000. And in that kind of salinity--fish die off so you basically have a microbial community. Everything else has been excluded because of salinity. And in this particular pond, where you have high salinity, you have this microbial mat forming a tiny, thin, dark layer on the top that is a layer of cyanobacteria - this little layer of cyanobacteria, which photosynthesizes for all they're worth. It's just a tenth millimeter in depth. Some of these layers have living organisms in, too, but in terms of photosynthesis, the action is in the active layer. There are more bacteria down here, and they live on whatever photosynthate they can get.
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