Another data point on the Fermi paradox

This Phys.org summary takes a while to get to the point, but it's an enlightening while. It doesn't quite explain everything it ought to explain, so I'll fill in the blanks for those of you who may need it.

Life on earth is something more than 3 billion years old. To be sure, Republicans don't believe this, but it is true. However, the metazoans -- a fancy name for the animals, that include us -- and plants haven't been around nearly as long, only (hah!) about 800 million years. We know that what made metazoan life possible was the rather abrupt enrichment of the earth's atmosphere with oxygen, which as I'm sure you have noticed animals need. This was brought about by an explosion in the population of photosynthetic organisms called cyanobacteria (often called by the misnomer "blue-green algae"). The cyanobacteria are still around, but they also made plants possible by getting themselves incorporated into plant cells as endosymbionts that today do the photosynthesizing work for your petunias.

The metazoans were made possible not only by the availability of oxygen, but also by another endosymbiotic event in which another line of bacteria became what are today the mitochondria, our cells' power plants. And plants also have those. Both kinds need a lot of phosphorous to thrive. The problem was, it wasn't around for the first 2 billion plus years, according to this new research -- or rather, it was sequestered deep in the ocean, where photosynthesis couldn't happen. Then TaDa! It showed up in substantial quantities in shallow coastal waters, cyanobacteria were in business, and 800 million years later, so were we.

This suggests that if whatever the key event was had not occurred, earth would still be inhabited by nothing but slime. It also suggests that many or most earth-like planets might never have hit the inside straight, which would help explain the Fermi paradox. It's also all the more reason not to do ourselves in. A) The environment that supports our kind of life is fragile and it can be screwed up and B) it may be quite rate in the universe so there' s nobody out there to carry on the cause of wondering about the universe and starting to understand it.  Let's take this historical moment very, very seriously.