How did complex life emerge and evolve on the Earth and what does this mean for finding life beyond Earth? This is what a recent study published in Nature hopes to address as a pair of researchers investigated how plate tectonics, oceans, and continents are responsible for the emergence and evolution of complex life across our planet and how this could address the Fermi Paradox while attempting to improve the Drake Equation regarding why we haven’t found life in the universe and the parameters for finding life, respectively. This study holds the potential to help researchers better understand the criterion for finding life beyond Earth, specifically pertaining to the geological processes exhibited on Earth.
Here, Universe Today discusses this study with Dr. Taras Gerya, who is a Professor of Earth Sciences at the Swiss Federal Institute of Technology (ETH-Zurich) and co-author of the study, regarding the motivation behind the study, significant results, follow-up studies, what this means for the Drake Equation, and the study’s implications for finding life beyond Earth. So, what was the motivation behind this study?
Dr. Gerya tells Universe Today, “It was motivated by the Fermi Paradox (“Where is everybody?”) pointing out that the Drake Equation typically predicts that there are from 1000 to 100,000,000 actively communicating civilizations in our galaxy, which is too optimistic of an estimate. We tried to figure out what may need to be corrected in this equation to make the prediction with the Drake Equation more realistic.”
For the study, the research duo compared two types of planetary tectonic processes: single lid (also called stagnant lid) and plate tectonics. Single lid refers to a planetary body that does not exhibit plate tectonics and cannot be broken into separate plates that exhibit movement by sliding towards each other (convergent), sliding past each other (transform), or slide away from each other (divergent). This lack of plate tectonic activity is often attributed to a planetary body’s lid being too strong and dense to be broken apart. In the end, the researchers estimated that 75 percent of planetary bodies that exhibit active convection within their interiors do not exhibit plate tectonics and possess single lid tectonics, with Earth being the only planet that exhibits plate tectonics. Therefore, they concluded that single lid tectonics “is likely to dominate the tectonic styles of active silicate bodies in our galaxy”, according to the study.
Additionally, the researchers investigated how planetary continents and oceans contribute to the evolution of intelligent life and technological civilizations. They noted the significance of life first evolving in oceans due to them being shielded from harmful space weather with single-celled life thriving in the oceans for the first few billion years of Earth’s history. However, the researchers also emphasize how dry land provides a myriad of benefits for the evolution of intelligent life, including adaptations to various terrains, such as eyes and new senses, which contributed to animals evolving for speed to hunt among other biological assets that enabled life to adapt to the various terrestrial environments across the planet.
In the end, the researchers concluded dry land helped contribute to the evolution of intelligent life across the planet, including abstract thinking, technology, and science. Therefore, what were the most significant results from this study, and what follow-up studies are currently in the works or being planned?
Dr. Gerya tells Universe Today, “That very special condition (>500 million years coexistence of continents, oceans, and plate tectonics) is needed on a planet with a primitive life in order to develop an intelligent technological communicative life. This condition is very rarely realized: only <0.003-0.2 % of planets with any life may satisfy this condition.”
Dr. Gerya continues, “We plan to study water evolution in the planetary interior in order to understand how stability of surface ocean volume (implying stability of coexistence of oceans and continents) can be maintained for billions of years (like on Earth). We also plan to investigate the survival time of technological civilizations based on societal collapse models. We also started a project on the oxygenation state evolution of planetary interior and atmosphere in order to understand how oxygen-rich atmospheres (essential in particular for developing technological civilizations) can be formed on planets with oceans, continents and plate tectonics. Progress in these three directions is essential but will greatly depend on the availability of research funding.”
As noted, this study was motivated and attempts to improve the Drake Equation, which proposes a multivariable equation that attempts to estimate the number of active, communicative civilizations (ACCs) that exist in the Milky Way Galaxy. It was proposed by in 1961 Dr. Frank Drake to postulate several notions that he encouraged the scientific community to consider when discussing both how and why we haven’t heard from ACCs and reads as follows:
N = R* x fp x ne x fl x fi x fc x L
N = the number of technological civilizations in the Milky Way Galaxy who can potentially communicate with other worlds
R* = the average star formation rate in the Milky Way Galaxy
fp = the fraction of those stars with planets
ne = the average number of planets potentially capable of supporting life per star with planets
fl = the fraction of planets capable of supporting and developing life at some point in its history
fi = the fraction of planets that develop life and evolves into intelligent life
fc = the fraction of civilizations who develop technology capable of sending detectable signals into space
L = the length of time that technological civilizations send signals into space
According to the study, the Drake Equation estimates the number of ACCs range widely, between 200 to 50,000,000. As part of the study, the researchers proposed adding two additional variables to the Drake Equation based on their findings that plate tectonics, oceans, and continents have played a vital role in the development and evolution of complex life on Earth, which are as follows:
foc = the fraction of habitable exoplanets that possess notable continents and oceans
fpt = the fraction of habitable exoplanets that possess notable continents and oceans that also exhibit plate tectonics that have been functioning for at least 500 million years
Using these two new variables, the study provided new estimates for fi (chances of planets that develop life and evolve into intelligent life). So, what is the importance of adding two new variables to the Drake Equation?
Dr. Gerya tells Universe Today, “This allowed us to re-define and estimate more correctly the key term of the Drake equation fi – probability of a planet with primitive life to develop an intelligent technological communicative life. Originally, fi was (incorrectly) estimated to be very high (100%). Our estimate is many orders of magnitude lower (<0.003-0.2 %), which likely explains why we are not contacted by other civilizations.”
Additionally, when inputting these two new variables into the entire Drake Equation, the study estimates a far smaller number of ACCs at < 0.006 to 100,000, which is in stark contrast to the original estimates of the Drake Equation of 200 to 50,000,000. Therefore, what implications could this study have on the search for life beyond Earth?
Dr. Gerya tells Universe Today, “It has three key consequences: (1) we should not hope much that we will be contacted (probability of this is very low, in part because the life time of technological civilizations can be shorter than previously expected), (2) we should use remote sensing to look for planets with oceans, continents and plate tectonics (COPT planets) in our galaxy based on their likely distinct (CO2-poor) atmospheres and surface reflectivity signatures (due to the presence of oceans and continents), (3) we should take care about our own planet and civilization, both are extremely rare and must be preserved.”
This study comes as the search for life beyond Earth continues to gain traction, with NASA having confirmed the existence of 5,630 exoplanets as of this writing, with almost 1,700 being classified as Super-Earths and 200 being classified as rocky exoplanets. Despite these incredible numbers, especially since exoplanets first started being discovered in the 1990s, humanity has yet to detect any type of signal from an extraterrestrial technological civilization, which this study referred to as ACCs.
Arguably the closest we have come to receiving a signal from outer space was the Wow! signal, which was a 72-second radio blast received by Ohio State University’s Big Ear radio telescope on August 15, 1977. However, this signal has yet to be received since, along with a complete lack of signals at all. With this study, perhaps scientists can use these two new variables added to the Drake Equation to help narrow the scope of finding intelligent life beyond Earth.
Dr. Gerya concludes by telling Universe Today, “This research is part of an emerging new science – Biogeodynamics, which we try to support and develop. Biogeodynamics aims to understand and quantify relations between the long-term evolution of planetary interiors, surface, atmosphere, and life.”
How will these two new variables added to the Drake Equation help scientists find life beyond Earth in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
This is an interesting idea, but the problem is most geoscientists think plate tectonics started in the meso-Archaean, not the Neoproterozoic. I know that Stern’s group has stuck with the latter viewpoint, but it does ignore quite a lot of evidence to the contrary, such as eclogitic diamonds, or isotopic evidence for the emergence of continental crust from the oceans in the meso-Archaean. Some, such as Korenaga, suggest plate tectonics may have started in the Hadean and there are good reasons to consider that much earlier date, plausible.
That said that plate tectonics has not had significant impacts on the evolution of complex life, is hard to refute, whether its the creation of complex landscapes, or the cycling of nutrients to and from the interior.
This is a common mixing of questions about complex body plan animal evolution and language capability evolution. The simpler observation lies within evolution itself, while biology split from geology almost immediately and diversify prodigiously it took a long time to evolve a small clade with language capable animals. It will naturally be a very rare occurence.
On a similar geophysical based hypothesis for complex organism evolution by Tarduino et al., Ben Slater from Uppsala University noted in a similar vein:
“Paleobiologist Ben Slater, however, sees things differently. Just because different events happen to happen at the same time, there does not need to be a causal relationship, he believes.”
“Nor does Ben Slater see it as a coincidence that the oxygen level in the atmosphere increased at the same time as the number of animal species increased. But he – and many paleobiologists with him – do not see the elevated oxygen level as a cause, but as a consequence.
– Before there were animals, the surface waters of the oceans should have been full of amounts of dead phytoplankton. When organic matter rots, oxygen is consumed. Therefore, oxygen levels never had a chance to build up, says Ben Slater.
When the animals came, all this changed. They began to feed on these phytoplankton and when they were lumped together in the animal’s digestive system, they became large enough to sink through the water. In this way, the animals removed the decaying organic matter and sent it down to the sea floor, where it was buried in the sediments.
– In this way, the oxygen could rise and ventilate the world’s oceans, says Ben Slater.
The increased oxygen content can thus just as well be explained by the development of complex animals as by something else. Moreover, in that case, this was not the first time that small organisms drastically changed the gas content of the atmosphere.
– Two billion years ago, oxygen levels increased for the first time in Earth’s history, but then thanks to cyanobacteria that produce oxygen as a by-product through their photosynthesis.
But then why did the number of animal species suddenly increase so much?
– Many researchers, at least in my field, believe that the cause was evolutionary and ecological. The emergence of animals and different species can be compared to a technological breakthrough where there is often no external “trigger”. Instead, it was just something that happened thanks to evolution, but which ultimately had very dramatic consequences.”
[“Därför exploderade jorden av liv”, Johan Nilsson, Dagens Nyheter, 19 May 2024]
And to chime in with stevenso4 and get away from the 500 million year date that the above paper also wanted to tie to a hypothesis of Earth core solidification, a new paper with quite good statistics claim cratonification started 3000 million years ago. [Reimink, J.R., Smye, A.J. Subaerial weathering drove stabilization of continents. Nature 629, 609–615 (2024). https://doi.org/10.1038/s41586-024-07307-1%5D First author Reimink has produced nice results before, and this paper suggests a rather flexible model.
“Contrary to previous interpretations, we infer that tectonic regime need not have changed from the Mesoarchaean to Neoarchaean period to account for the geological evolution of Archaean cratons. Instead, the mechanism
proposed implies that craton stabilization was activated by continental emergence, which, in turn, was driven by one of several viable processes unrelated to tectonic transitions54–58. The geological record can then be cast in terms of a pre-emergence (TTG-dominated) and post-emergence (granite-dominated) planet.” The TTG-dominated Earth had a global ocean, the granite dominated has not.
But of course their framework is just a model. “The scientists said future work will involve sampling ancient interiors of cratons and, perhaps, drilling core samples to test their model.” [“The Craton Enigma: Scientists Propose a New Continental Formation Theory”, Penn State, MAY 11, 2024]
The last comment became a bit cryptic. It was the Tarduino et al. paper that throws in a claim on core solidification.