Until recently, researchers believed only one planet in our solar system had plate tectonics: Earth. But in , Brown University researchers used atmospheric modeling to show that Venus, much of whose geological history is a mystery, once had plate tectonics 鈥� the composing its surface 鈥� not entirely unlike present-day Earth.
鈥淲hen we look at Venus, we actually see the aftermath of the end of plate tectonics, so 鈥� we are looking at potentially the future of the Earth,鈥� said Matthew Weller, the study鈥檚 first author, current Urey Fellow at the Lunar and Planetary Institute in Houston and former postdoctoral research associate at the University.
Almost all of Venus鈥檚 surface area was formed in the last half-billion years. The study grapples with Venus鈥檚 history prior to the crust observed today.
While Earth and Venus are 鈥渟ister planets鈥� in size and Milky Way neighbors, the planets are opposites in every other way, according to Weller. Venus has an atmosphere 93 times denser than Earth鈥檚 with toxic carbon dioxide levels, as well as a surface temperature of 867 degrees Fahrenheit.
Like every other planet in our solar system except Earth, Venus has a 鈥渟tagnant lid鈥� regime, meaning there is no physical movement of portions of Venus鈥檚 crust, said co-author Daniel Ibarra, assistant professor of Earth, environmental and planetary sciences and environment and society. Earth, by contrast, has an 鈥渁ctive lid,鈥� meaning the crust is divided into plates that slide back and forth, Ibarra said.
鈥淲hen the sun formed 鈥� and the planets formed, (Venus and Earth) were probably under pretty similar conditions,鈥� said Professor of Earth, Environmental, and Planetary Sciences James Head PhD鈥�69, who was not involved in the study. Despite the planets鈥� similarities, studying Venus is still a big challenge. 鈥淵ou're not in Kansas anymore,鈥� Head said.
鈥淗ow did these two otherwise similar planets evolve so fundamentally differently, one a hellish landscape, one perfect for life?鈥� Weller said. 鈥淭hat鈥檚 what the study we did is trying to address.鈥�
Because a planet鈥檚 atmosphere is largely composed of gases that leave its mantle, 鈥渨e can tell a lot (about a planet鈥檚 tectonics) by understanding the composition of the atmosphere,鈥� said Head.
There are two main theories explaining Venus鈥檚 current composition. The first is that its atmosphere traces back to the initial release of gases at the very origin of the solar system and has remained stable since then. According to Weller, that might not be "terribly realistic.鈥�
The other theory proposes that Venus was once more habitable and that its current atmosphere came to be later due to 鈥渃atastrophic overturning or transient tectonics,鈥� Weller explained.
鈥淲e showed that it's actually potentially in the middle鈥� of the two theories, Weller said. 鈥淭hat if you started in plate tectonics very, very early on, a natural consequence is exactly a Venusian atmosphere.鈥�
The study examines atmospheric nitrogen because the gas鈥檚 long shelf life allows for extensive analysis of and tectonic history.
The researchers modeled Venus鈥檚 history, assuming either active plate tectonics or stagnant lid throughout the evolution of Venus to see what atmosphere would have been produced. A plate tectonics history is more similar to Earth, while a stagnant lid is more similar to Mars or Mercury.
鈥淲e actually found that the only way we could match current Venusian nitrogen abundances, and CO2 levels as a secondary characteristic, was through plate tectonics,鈥� Weller said. 鈥淪pecifically, an early phase of plate tectonics would have had to last at least a billion years.鈥�
So why does understanding if Venus had plate tectonics matter?
According to Weller, existing research suggests that 鈥渢he proliferation and long-term habitability of a planet is directly tied to plate tectonics.鈥� That鈥檚 in part because Earth, the sole planet with known life, is also the only one with known active plate tectonics. Plate tectonics impact the cycling of volatiles 鈥� readily vaporizing materials in the mantle 鈥� like water and CO2, many of which are key for life.
鈥淲hat plate tectonics does is 鈥� bring materials in and then back out (from the Earth鈥檚 crust), so it doesn't lock them away where life can't get to them,鈥� Weller said. 鈥淚t keeps them mobile for life to be able to access this energy and food sources.鈥�
The researchers originally developed their model to study how exoplanets, or planets , form their atmospheres, Ibarra said.
Studying exoplanets can both reveal insights about Earth itself and put forward other questions: 鈥淎re there other habitable worlds? If there are 鈥� (and) there likely are 鈥� how many are there?鈥� Ibarra added.
鈥淏eing able to use the atmosphere of Venus to infer the inner workings of the planet is really important when we look at these extrasolar planets,鈥� Weller said. 鈥淲e might be able to infer that there is plate tectonics, that there's liquid water and maybe even life.鈥�
