Today’s New Reason To Believe

Jeff Zweerink, Ph.D.

How common is life in the universe? The quest to answer that question drives a substantial amount of research in a broad number of disciplines.

Astronomy provides input on the rate at which habitable planets form. Geology informs the astronomy regarding what makes a planet habitable. Biology studies how life operates in various environments. Chemistry addresses how life-critical chemical reactions proceed in different conditions. Cosmology and physics constrain the universe’s ability to support life.

An article in Astrobiology tries to quantify the rarity of complex life in the Milky Way Galaxy. The authors develop a model of Earth-analog planets which incorporates tectonic activity, the increase in stellar luminosity, and the interaction of geological, biological, and atmospheric processes thataffect the carbon dioxide content of the atmosphere. The model seeks to address how these processes affect both simple, single-celled life and more-complex multicellular life. Researchers evaluated the habitability of the Earth-analogs by considering the capacity of the planet to sustain liquid water and to maintain a sufficiently low atmospheric carbon dioxide concentration.

A few of the paper’s conclusions are worth highlighting.

1. The models demonstrate that the requirements of complex life make habitable analogs at least a hundred times less frequent than planets that could support simple life. RTB’s creation model predicts this conclusion. In fact, RTB’s model predicts that the planets capable of supporting complex life will be many more orders of magnitude less (lots of zeroes) than even this initial study finds.

2. The paper finds that the number of potentially habitable planets peaked nearly two billion years ago. RTB’s model also predicts that habitable planets formed only during a brief period of time in cosmic history. Additional research should demonstrate that this time window will continue to narrow as scientists better understand what makes and keeps planets habitable.

3. The study also finds a steadily decreasing overlap between the liquid water habitable zone and the habitable zone with appropriate concentrations of carbon dioxide in the atmosphere. Again, this finding comports well with RTB’s creation model.

Although the paper argues that telescopes within the next decade have a reasonable chance of finding planets with complex life, those results depend on at least one optimistic assumption (which the authors note). That assumption states that where liquid water, carbon, and some nutrients are available, microbial life is inevitable. However, the authors also acknowledge that many scientists argue that “the fraction of habitable planets that may evolve life is extremely low.” Obviously, RTB’s model advocates for the latter view.