The Shadow Biosphere: Is There Other Life on Earth?

In the search for understanding life in all its forms, current scientific definitions may be ill-equipped to recognize life that operates outside the parameters we have long considered standard.

The current consensus definition of life is narrow and may fail to recognize alternative forms of life.

Josh Clark points out that the current definition of life does not comprehensively cover all known forms such as humans, microbes, and birds. This inadequacy is especially pertinent to researchers interested in the concept of a shadow biosphere. Chuck Bryant explains that the search for life is often limited to Earth-like conditions, which could prevent the discovery of life forms that exist under different conditions.

Carol Cleland proposes that there could be unfamiliar life forms that we do not recognize because they do not fit within the constraints of our recognized definition of life. Clark introduces the concept of "life with a Y," a broader categorization that might encompass not only the life we are familiar with but also potential members of a "shadow biosphere."

The consensus definition asserts that life must be carbon-based, use DNA/RNA for programming, be constructed from amino acids and proteins, have the capability for self-replication, and evolve according to Darwinian principles. This narrow view is potentially exclusive, possibly ignoring life forms that may not use DNA or RNA, use amino acids—particularly those unknown to current science—or may not even be carbon-based.

The central dogma of biology may not account for all possible li ...

The concept of life’s diversity expands as scientists consider the possibility that life elsewhere might utilize a broader range of molecular components than just the ones found in terrestrial biology, leading to different biochemistries.

Life may be possible using different nucleic acids and amino acids beyond those found in terrestrial biology.

Josh Clark talks about the traditional hypothesis of the primordial soup and the building blocks of Earth-based life but suggests alternative chemical compositions could potentially kickstart life.

Scientists have proposed the possibility of "Hachimoji DNA" using additional base pairs beyond the standard A, T, C, G.

DNA and RNA are recognized for their specific nucleic acid base pairs, but the existence of additional nucleic acids raises the question of their potential as life's building blocks. The podcast discusses Hachimoji DNA, which includes the standard four base pairs (AT and GC) and adds an additional four (P, Z, D, and S). Experiments show that ribosomes can transcribe these new nucleic acid arrangements, indicating the plausibility of life evolving with different amino acids through mechanisms similar to those on Earth.

There are over 500 known amino acids in nature, but life on Earth only utilizes 20.

Life on Earth is known to be built from 20 amino acids, but more than 500 different amino acids on Earth point to the possibility of different combinations supporting diverse forms of life. The discovery of meteorites containing up to 80 other amino acids strengthens the idea that there could be alternate sources of amino acids capable of fostering alternative life forms in the universe.

Chirality, or "handedness", of biomolecules may not be a universal requirement for life.

Life as it is known consistently uses left-handed amino acids and right-handed sugars. There are, however, molecules with o ...

Josh Clark and Chuck Bryant dive into the concept of a shadow biosphere, where unconventional forms of life might exist undetected due to our narrow search parameters based on known life.

Microbes are the most likely candidates for a "shadow biosphere" on Earth.

Clark and Bryant discuss the possibility of "shadow microbes," based on Carol Cleland's theory that life might have originated multiple times under different conditions. This shadow biosphere could contain organisms composed of elements or structures differing from conventional life forms. Such life could have eluded detection because scientific methods are designed to find life as we traditionally understand it. As evidence, they point to extremophiles, which have adapted to environments previously thought uninhabitable, suggesting that entirely different life forms might exist.

Detecting such a shadow biosphere would have significant implications for our understanding of life in the universe. If diverse forms of life developed independently on Earth, it would imply that biology is a universal law and that life is likely common throughout the cosmos.

Microbes are small, difficult to detect, and we have only characterized a tiny fraction of microbial diversity on Earth, leaving ample room for undiscovered life forms.

Clark and Bryant agree that if a shadow biosphere exists, it most likely consists of microbial life forms due to their small and often hard-to-distinguish features. Scientists have cultured and described less than 1% of microbial species, suggesting vast potential for undiscovered organisms in the remaining 99%. Cleland, while observing molecular biologists in Spain, speculated on our ability to recognize entirely new forms of life, hinting that unconventional life could easily be overlooked with current methodologies.

Extreme or understudied environments may harbor undiscovered life.

The hosts discuss environments inhospitable to known forms of life as likely places to search for shadow biosphere organisms, such as the Dead Sea's high salinity, or areas of extreme temperature, acidity, and radiation. Researchers have already discovered bacteria in environments exceeding 122 degrees Fahrenheit and organisms in highly radioactive settings like abandoned uranium mines and the Chernobyl reactor.

Locations that seem inho ...