A new paper taking a look at the Fermi Paradox using the Drake Equations has suggested an uncomfortable solution: maybe we are alone in the galaxy.
If you haven’t heard of the Fermi Paradox, it goes something like this: given the vastness of the universe and the probability that implies of life evolving elsewhere, how come no alien civilization has ever gotten in touch? We have found many exoplanets in the brief time we’ve been looking. Surely there must be someone else out there who, like us, desperately wants to find others?
Since it was posed in 1950 by Enrico Fermi, there have been a range of answers, from the benign to the absolutely terrifying. One is that there simply hasn’t been enough time yet. Alien civilizations may prioritize, as we do, searching for techno signatures, which we simply haven’t been broadcasting for long enough.
On the other end of the spectrum, it could be that the tendency throughout the universe is for civilizations to destroy themselves before they reach sufficient advancement to make contact.
After the Fermi paradox came the Drake Equation, which attempts to quantify the number of intelligent civilizations in our galaxy, or the universe. In it, we can place knowns or best guesses as to the number of stars that contain (for instance) planets in habitable zones, or best guesses as to how many of those will be able to sustain intelligent life.
Using these equations, scientists attempt to estimate the number of intelligent civilizations in the universe, and depending on their input, have come up with answers ranging from 30 to 100,000. Drake himself estimated a figure between 1000 and 100,000,000 in our galaxy alone.
As we get more information on exoplanets, and how life began here on Earth, we can at least refine our estimates, which is what a new paper attempts to do. These high estimates do not fit with what we see – i.e. no active, communicative civilizations (ACCs) – the researchers point out, and so perhaps we are missing some important variables.
The team attempted to address this by looking at how life evolved on Earth. Like many others, they suggest that plate tectonics is crucial for complex animals to evolve. Plate tectonics, the team explained, likely accelerated biological evolution in several key ways. This includes delivering crucial elements for life like phosphorus to the surface.
“Tectonic processes exposing fresh rocks on the surface are crucial for enhancing delivery of [phosphorus] and other inorganic nutrients, because shielding of fresh rock surfaces by soil reduces nutrient fluxes due to chemical weathering,” the team explains in their paper, adding that evidence for this is found in Earth’s ancient history, where the emergence of plate tectonics created a more life-hospitable environment.
“The addition of [phosphorus], [iron] and other nutrients from erosion and weathering of Ediacaran collisional mountains broke the Mesoproterozoic nutrient drought, stimulating life and evolution.”
The transition to plate tectonics may have been crucial in other areas too, including increasing oxygen levels in the atmosphere and ocean, moderating the climate (e.g. through subduction of carbon), and creating complex landscapes and climates that can stimulate diversity of life.
“We further suggest that both continents and oceans are required for ACCs because early evolution of simple life must happen in water but late evolution of advanced life capable of creating technology must happen on land.”
It’s possible that plate tectonics – as well as sufficient oxygen for a planet to have fire – is necessary for intelligent, communicative life to appear. Thus, we should look for planets with continents and plate tectonics that can be sustained over long enough time periods for life to evolve.
The team then attempted to place restrictions on the amount of water that would need to be present on exoplanets in order to have surface water and continents, before attempting to use the Drake Equation to estimate how many planets in the galaxy contain these conditions (and others), making them potentially suitable to evolve ACCs.
They came up with a figure ranging from less than 0.006 to less than 100,000. But this is not the only limiting factor to ACCs, with other potential “great filters” coming later for life, such as potential extinction events or societal collapse.
Factoring this in, they put the figure between less than 0.0004 and less than 20,000. The team stresses that we should probably look at the lower end of this range, given that potential catastrophes could limit the amount of time alien civilizations are communicative for.
“It may be that primitive life is quite common in the galaxy,” the team concluded. “However, due to the extreme rareness of long-term (several hundred of million years) coexistence of continents, oceans and plate tectonics on planets with life, ACCs may be very rare.”
There are, of course, a whole host of uncertainties within the Drake Equation that can be updated as we learn new information. Large planets are much easier to detect than Earth-sized terrestrial planets, due to the increased amount of dimming and wobble they produce on their host stars.
Perhaps there is an abundance of Earth-like planets which we will find as detection improves, or other planets capable of hosting life. Or we could find that initial life is more likely than we thought, making it more likely that life could get through these great filters somewhere in the cosmos.
Though plate tectonics may play a huge role in our own evolution, let’s not lose hope that there are others out there with intelligence just yet.
The study is published in Scientific Reports.
