The start of the deep carbon cycle on Earth was vital to creating a planet where life could evolve and thrive, but carbon doesn’t tell the whole story. The recycling, distribution, and storage of other bio-essential elements, including nitrogen, oxygen, sulfur, phosphorus, and hydrogen, also play a crucial role in making a planet habitable.
With the formation of the CLEVER Planets (Cycles of Life Essential Volatile Elements in Rocky Planets) project, Rajdeep Dasgupta (Rice University, USA) is leading a multidisciplinary initiative to understand how these various chemical cycles function and interact to create a surface environment amenable to life on Earth and other rocky planets. In late 2018 Dasgupta received a five-year, $7.7 million grant from NASA’s Science Mission Directorate and also became part of their Nexus for Exoplanet System Science network, a collection of research groups studying the potential for life on planets outside our solar system. The initiative includes fellow DCO researchers Laurence Yeung, Kyusei Tsuno, Damanveer Grewal, (all at Rice University, USA), Tom McCollom (University of Colorado Boulder, USA), and Bernard Marty (Centre de Recherches Pétrographiques et Géochimiques, France).
“The overall goal of this project is to understand the concept of chemical habitability,” said Dasgupta. “We are trying to understand how different rocky bodies might get enough life-essential elements and partition the elements in a way so that they are available at surface conditions where they can help life emerge and flourish.”
Dasgupta has maintained a longstanding interest in the cycling of volatile elements, like carbon, nitrogen, and sulfur, and so his research goals have naturally aligned with those of the DCO. He said that being active in DCO has helped put him in a better position to lead this new initiative.
“I think the most fascinating thing is truly the interdisciplinary approach of this project,” said Dasupta. Team members include astronomers, astrophysicists, geophysicists, geochemists, and petrologists. “We are trying to develop a collaboration that brings concepts and understanding from one subdiscipline to another and to tackle problems that lie at the interface.”
Dasgupta and his colleagues have already published several articles as a result of their work with the Clever Planets project. In a paper in Geochimica et Cosmochimica Acta , they show that the presence of sulfur decreases the amount of carbon that ends up in the core as a new rocky planet forms. In a recent study  in Science Advances, they propose that a body the size of Mars crashed into early Earth, and delivered bioessential elements necessary for life, while also breaking off enough material to make the Moon. This delivery of sulfur ensured that Earth’s carbon ended up at the surface where it was available for life. In another new paper in Geophysical Research Letters , they explore how the presence of nitrogen in the core would impact the movement of seismic waves, and conclude that nitrogen is likely only a trace or minor element in Earth’s core. Most recently, in a new paper in Earth and Planetary Science Letters , they combine several models of the mantle to predict how plate tectonics evolved on Earth. The models suggest that carbon recycling must have occurred for most of Earth’s history to explain current levels of carbon dioxide degassing at mid-ocean ridges, where new seafloor forms.
Much of this research draws on data from Earth and the nearby rocky planets, Mercury, Venus, and Mars. But ultimately, the CLEVER Planets researchers hope to understand the habitability of distant rocky planets orbiting other stars. This work will help scientists to identify environments as well as time periods during a planet’s evolution that are most likely to be inhabitable and will assist in the search for life beyond our solar system.
Main image: These 20 swirling balls of gas and dust, called protoplanetary disks, were captured by the ALMA radio-telescope array in Chile. The disks that will one day coalesce into planets. Credit: Andrea Isella