So far, our long search for signs of extraterrestrial life has been fruitless. Two geoscientists now think they know why. It has to do with the Earth’s tectonic plates.
Robert Stern of the University of Texas at Dallas and Taras Gerya of the Swiss Federal Institute of Technology say that tectonic plates are one key reason why life has thrived on Earth.
“Life has been around on Earth for about four billion years, but complex organisms like animals didn’t appear until about 600 million years ago, which is not long after…plate tectonics began,” explains Stern.
Stern says that plate tectonics “jump-starts the evolutionary machine.” As the plates move, they create oceans, mountains, and volcanoes. This generates weather systems and a variety of climates, which causes weathering, washes nutrients into the oceans, and boosts marine life. Tectonics indirectly also sped up the creation of oxygen in our atmosphere. On land, habitat turnover through climate change forced different species to evolve far more quickly than they otherwise would have.
A rare feature of Earth
Plate tectonics is rare. Earth is the only planet in the solar system with them. If this holds true for the wider galaxy, it could explain why we have not found life elsewhere. The plate tectonics that helped us evolve are absent everywhere else, as far as we know.
Based on their findings, the two researchers believe the Drake Equation should be adjusted. Formulated in 1961, the Drake Equation estimates the number of civilizations in the Milky Way that could communicate with humans. Essentially, it churns out the odds of us finding intelligent life elsewhere in the galaxy.
It considers several variables: the number of stars that form each year, how many of them have planets, and how many of those planets could feasibly sustain life. Other variables are more speculative: How many planets show signs of life, how often that life becomes intelligent, and how many life forms can then make a technology that allows them to communicate their existence.
Making sense of the Drake Equation
The Drake Equation is by no means a perfect formula. The main issue is that astronomers do not have accurate figures for all those variables. However, estimates by many scientists suggest that we should have found life somewhere by now.
“Previous estimates for the lower limit of the number of civilizations in our galaxy were rather high,” Taras Gerya told Space.com.
Stern and Geyra think the formula contains a slight error: It does not factor in whether planets have tectonic plates. Stern and Geyra think that one of the variables in the equation — something called fi , which equals the number of exoplanets that develop intelligent life — needs to change. They argue that it should be the product of two factors: the fraction of planets with both continents and oceans and the fraction of planets with plate tectonics.
In the original formula, the value for fi is almost 1, which makes finding intelligent life very likely. Their estimates reduce that variable to between 0.003% and 0.2%. Their conclusion: Intelligent life might be far rarer in the universe than we ever thought.
