The Rare Earth hypothesis offers science-based reasons that life in the universe is rare
Last week, we looked at the hypothesis that, to avoid the heat destruction of their advanced technology, the aliens have put themselves into a digital slumber until the universe cools down.
This week, let’s look at a quite different approach, which Williams outlines in “Beyond “Fermi’s Paradox” IV: What is the Rare Earth Hypothesis?” (July 29, 2020): That is “the possibility that life-bearing planets like Earth are just very rare.” We don’t see aliens because they are very uncommon:
This is what is popularly known as the “Rare Earth Hypothesis,” which argues that the emergence of life and the evolution of complexity require a combination of astrophysical and geological conditions that are simply not common in our Universe. This contradicted previously-held notions by prominent scientists and SETI researchers, who were of the opinion that Earth was typical of rocky planets located throughout the Universe.
As Williams points out, the term “Rare Earth”* was popularized by an influential 2003 book called Rare Earth: Why Complex Life is Uncommon in the Universe. It’s authors are paleontologist Peter Ward and astronomer Donald E. Brownlee at the University of Washington.
The duo questioned a central assumption made by Carl Sagan (1934–1996), Frank Drake and the (and Search for Extraterrestrial Intelligence ’s) iconic Drake Equation: of 1961, that not only are They Out There but there are Lots of Them.
Ward and Brownlee revised their famous Equation and added in factors known to be true of Earth but maybe not easy to find elsewhere and came up with a much lower figure:
For a number of reasons, Matt Williams does not like the Rare Earth hypothesis. Concluding a list, he writes:
On top of all that, scientists have questioned the definition of “habitable zone” in recent years, with some suggesting it could be a lot narrower than previously thought. Other research has indicated that habitable planets could also be found in longer orbits, indicating that HZs are actually wider. It’s also possible that Earth does not represent the pinnacle of habitability and there may be a class of “superhabitable” worlds.
Considerable research has also been dedicated to how our very notion of habitability is based entirely on Earth’s current geological period. At many junctures in the past, atmospheric and climatic conditions were significantly different on Earth than they are today. And yet, these conditions are believed to have been essential to the evolution of life at different stages.MATT WILLIAMS, “BEYOND “FERMI’S PARADOX” IV: WHAT IS THE RARE EARTH HYPOTHESIS?” AT UNIVERSE TODAY
Of course, no one can rule out the possibility that entities that we would not recognize as life but really are life exist in abundance in the universe. For one thing, there are many definitions of “life” as we do know it:
Abstract: Despite numerous and increasing attempts to define what life is, there is no consensus on necessary and sufficient conditions for life. Accordingly, some scholars have questioned the value of definitions of life and encouraged scientists and philosophers alike to discard the project. As an alternative to this pessimistic conclusion, we argue that critically rethinking the nature and uses of definitions can provide new insights into the epistemic roles of definitions of life for different research practices.– BICH, LEONARDO AND GREEN, SARA (2016) IS DEFINING LIFE POINTLESS? OPERATIONAL DEFINITIONS AT THE FRONTIERS OF BIOLOGY. SYNTHESE. ISSN 1573-0964
But the Drake Equation that is our starting point addresses the question in terms of accepted assumptions about the elements and conditions needed for life. Departing too far from those terms may render the problem both undefinable and unresearchable.
A critic at Futurism points out that life forms are adaptable:
Over millions of years, species have evolved to adapt to their environment. We have fish and other exotic forms of life that can survive under immense pressures within the deepest depths on the ocean floor. We have algae that can survive in boiling temperatures. Then, we have the lovely tardigrades (also known as water bears), which can survive IN THE VACUUM OF SPACE.
So life could thrive in environments much different than that of our own blue marble. On top of this, there are more and more Earth-like exoplanets being discovered each day, just within our galaxy alone. This doesn’t necessarily mean that Earth-like life has a fighting chance on any of them, but it also doesn’t mean that there never will be!
Indeed, but the whole concept of adaptability is defined on life forms considered as descendants of Earth. It does not by itself imply that there are any others out there…