Yes I do, but we shouldn't be disappointed to find a universe teeming with mostly bacteria! When you study just how soon after the Earth formed the Earth ended up with single celled bacteria and algae ( 3.8 billion years ago is the oldest fossil remains of these organisms, and at that time the Earth was only a few hundred million years old) you get the sense that organic life is awfully tenacious, but for our planet, it spend nearly 99 percent of its history locked in this phase of life form evolution.
Astronomers have already discovered dozens of planets orbiting other stars. I think it is very likely that in some of those solar systems there are planets that at least have thriving bacteria! The next step is hard. The first multi-cellular animals appeared on the Earth only about 600 million years ago AFTER the algae had already used photosynthesis to increase the free oxygen level in the atmosphere. If this hadn't happened, if the algae had decided on producing some other waste product like methane, then our kind of life would never have happened.
The reason you need free oxygen is that it is a very chemically active gas that leads to lots of chemical reactions necessary for life. If the organism is too large, the cells deep inside the organism cannot get enough oxygen to themselves and they die. Without free oxygen, you are limited it seems to only very simple bacteria and organisms with a hand full of cells. BUT if the organism learns how to respire and creates a circulating blood system, it can grow very big since now there is a way of supplying every cell with oxygen extracted from the air and water.
Copyright 1997 Dr. Sten Odenwald
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