Searching for Clues about Cell Origins

     I planned to write three or four articles about the origin of our kind of cells. The cells we are made of are called “eukaryotic” cells, meaning cells with a nucleus inside. But this topic turns out to have a life of its own. The more I think about it or research it, the more there is to say.
      Our species, Homo sapiens, has been on this planet for perhaps 100,000 years, at most 200,000. We know this because we have been able to retrieve and date human fossils: mummies, bones, or tools.
      We can also find and date fossils of other organisms, but this gets harder to do the longer ago the organism lived. All sorts of interference occurs. An organism may die in a location where its body immediately decays without a trace. It may die and be buried in a way that preserves some parts, hard ones like shell or bone or wood. But later geological activity, like mountain building, earthquakes, volcanoes, or erosion, may expose the fossil parts to decay or may destroy them.
      Finding and dating fossils gets much harder with organisms that didn’t have any hard parts. Yet, remarkably, some of these still leave traces, including bacteria, soft. one-celled, microscopic creatures. Some cyanobacteria (photosynthetic green bacteria from as early as 3.5 billion years ago) left stromatolites for us to find. These are stacks of calcium carbonate deposits that resulted from photosynthesis reactions. Photosynthesis removed carbon dioxide from the sea water in which the photosynthetic bacteria lived, and tiny particles of calcium carbonate powder resulted. This calcium carbonate deposited on top of the bacteria. As the bacterial cells reproduced by splitting in two, new cells remained on top of old cells. Cells by the thousands and millions and billions stacked up, and calcium carbonate deposited on each layer. And that’s what stromatolites look like. They look like rock built up out of layers and layers of material.
      Other such soft, one-celled, microscopic creatures left fossil traces. But a huge number did not. And even the traces we find may not tell us much about the inner workings of these single cells. So the puzzle is: what was going on inside the earliest cells to ever live on earth? We want to know, because we want to follow their evolution. There are clues. But these clues are a completely different kind of “fossil.” I’ll begin to talk about them in my next article.