World-building is a critical component of science fiction and fantasy. For me, creating other worlds and the societies that inhabit them is what inspired me to write science fiction in the first place. In my mind, even the most exotic worlds should be based on science. That said, things can get pretty weird.
In this blog, we’ll look at some of the extremes under which life can exist. Maybe the better question would be, under what conditions could it NOT exist? Extreme levels of several elements seem to present barriers to the development of advanced life. Life may survive under extreme conditions, but in a reduced state of metabolism similar to hibernation. Some seeds and microbes can sustain life for years while waiting for more suitable environmental conditions. On the other hand, there is ample proof that some life thrives within certain boundaries. However, if an environment shifted from moderate to extreme over a long period of time, more advanced organisms might be able to develop adaptations, especially in terms of finding or building suitable habitat.
The key elements that serve to inhibit life include lack of water, salinity, alkalinity/acidity, temperature, radiation, pressure (air and water), and poisons. For each of 
these elements, there is at least one organism on earth that can withstand extremes. Salinity and oxygen are two that readily allow the development of advanced life forms, so for the purposes of my blog, I will dismiss those. Given enough time, it wouldn’t surprise me to have dolphins, whales, and maybe octopi join us as sentient lifeforms (if they haven’t already, and we’re just too stupid to know it). If you don’t know why I included octopi, do some reading on these amazing creatures—my top pick for inspiration in alien life.
Water
Water seems to be a critical limiting factor, enough so that NASA is using the presence of liquid water as its primary focus in seeking extraterrestrial life. The Atacama desert in Chile is one of the oldest, driest, hot deserts on Earth, with areas receiving on average less than 15 mm of rain per year, and other areas receiving no rain at all for years at a time.
In 2003, a team of researchers published a report in which they duplicated the tests used by the Viking 1 and Viking 2 Mars landers to detect life, and were unable to detect any signs in Atacama Desert soil in the region of Yungay. The region may be unique on Earth in this regard, and is being used by NASA to test instruments for future Mars missions. Later, however, the team duplicated the Viking tests and found that they missed signs of life in soil samples from Antarctic dry valleys, the Atacama Desert, and other locales. However, in 2014, a new hyperarid site was reported, Maria Elena South, which was much drier than Yungay. (Wikipedia)
Nonetheless, life flourishes on the borders of the Atacama Desert. Fog from the ocean is common and produces pools or lakes called lomas, which provide a water source. (Photo by Leon Petrosyan on Wikipedia) Over 500 species of flora have been gathered within the border of this desert. Some are succulents that can store water, and others have adapted to postpone periods of growth and flowering until rain does fall. Animals such as the leaf-eared mouse, guanacos, the South American gray fox, several species of birds, lizards, beetles, and wasps have also adapted to living there.
People in the Atacama have a history of collecting water from the air. For hundreds of years, native people in the Andes harvested water by capturing the morning dew. They dug pits into the ground to hold buckets and made funnels from branches to channel water into the buckets. Lids made of branches and leaves kept the water from evaporating. The trap was left overnight and the water collected in the morning after dew formed. They have also been capturing water from fog for over a decade using screens that have very small mesh. The water in the fog condenses on the screens and drips into troughs below. Pipes carry the water to where it will be used. The idea caught on and now there are fog collectors installed in 25 countries in Africa, South and Central America, the Caribbean, and Asia. How’s that for a great world-building idea? https://www.windows2universe.org/vocals/water_clouds.html
Temperature:
The upper limit for DNA and chlorophyll is about 158 degrees F (70o C), and the lower limit is about 5o F (-20o C). The lowest temperature for active microbial communities is about -0.4o F (-18o C). Below these limits, many organisms can survive, but at reduced metabolic states. https://space.nss.org/life-in-extreme-environments/ I have to say, when I did my research, these limits blew my mind. I expected a much broader range. Cold-blooded creatures like frog and turtles use water frozen outside their cells to insulate them, but they remain dormant at colder temperatures. Other organisms must have special proteins, cryoprotectants, to allow them to survive thawing, or must be able to produce molecules that lower the freezing point of water.
In case you’re wondering, when a human is placed in cryogenic suspension, all the water must first be removed from their cells and replaced with a cryoprotectant. https://science.howstuffworks.com/life/genetic/cryonics2.htm
Penguins use a combination of blubber and feathers to insulate them against the Antarctic cold. Emperor Penguins can withstand temperature at the bottom of the temperature range, down to -20o C (-4o F).
Tardigrades, commonly called “water bears,” can survive temperatures from -391o F (-235o C) to 304o F (151o C) in hibernation mode. They can also survive up to 6,000 times the atmospheric pressure at sea level. Don’t let the photo fool you—this guy’s a lot smaller than he looks. This was taken with an electron microscope. (Photo from ame616.tumblr.com on Pinterest) I really want to pet one!
On earth, the only organisms that thrive at extremely high temperatures are Archaea or Bacteria (some have even been found in volcanic vents!), but some Eukaryotes can thrive at low temperatures and extremes of high acidity or alkalinity, pressure, and salt. Eukaryotes have a nucleus surrounded by a cell membrane and include all higher life forms.
Other metabolic dangers
Substances such as mercury, arsenic, cadmium are toxic to most earth life. Humans have used small amounts of poisons such as snake venom and even arsenic to develop resistance to such toxins. Oxygen is also toxic to some earth life forms, known as anaerobics.
If humans can train their bodies to resist toxins within the space of a single lifetime, what could they accomplish over generations? With a carefully crafted world, almost any environment could be made believable. Make it more real by thinking carefully about how your people adapted. What are their homes like? What do they eat? What health problems do they suffer?
Radiation also damages DNA, though some microbes seem to be resistant to that as well.Scientists are fairly certain that microbes even survive the rigors of space on asteroids. Could an advanced life form develop a similar ability? How long would that take? The first human ancestors appeared about 2.5 million years ago. Homo erectus was the first to migrate out of the comfortable environment of Africa about 1.9 million years ago, and Homo sapiens didn’t appear until about 300,000 years ago. How would we have developed if radiation levels had gradually increased over that time?
Enjoy your new world.
Thanks for visiting. Join me again next week for more world-building science.
