Astrobiology

Did Earth’s Multicellular Life Depend on Plate Tectonics?

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!

Laurence Tognetti

Laurence Tognetti is a six-year USAF Veteran who earned both a BSc and MSc from the School of Earth and Space Exploration at Arizona State University. Laurence is extremely passionate about outer space and science communication, and is the author of “Outer Solar System Moons: Your Personal 3D Journey”.

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