NASA’s Curiosity rover and its mission to investigate whether Mars could have ever supported microbial life have taken one step closer to achieving its goal, with one of the most significant discoveries in the ongoing search for evidence of life on the Red Planet.

While exploring Gale Crater, NASA’s robotic rover uncovered a sample in 2020 and, using a chemical technique, determined that 21 carbon-based molecules were preserved in the clay-rich sedimentary rock. This also included seven that had never been identified on Mars before. 

While the discovery does not definitively point to life on the Red Planet, it does strengthen the case that Mars has the chemical conditions to support life. 

According to scientists, the most remarkable aspect of the discovery is not the molecules themselves, but their preservation

“The actual organic components they found are not strong evidence for life,” said Texas A&M University astrobiologist and geobiologist Dr. Michael Tice in a statement. Tice acknowledged that these compounds may also have evolved through abiotic processes, including formation in meteorites or other non-biological pathways.

“These organics were likely preserved in the rocks for a very long time, possibly billions of years, despite radiation and other harsh conditions on Mars,” Tice said.

“It blows my mind.”

Building Blocks of Life

Organic molecules are critical building blocks of life, but they can also form through non-biological processes, such as geological reactions or meteorite delivery. Similar preserved compounds on Earth help scientists study ancient environments, and their discovery on Mars provides new clues about the planet’s billion-year-old history.

“Studying how those compounds vary between different rocks can tell a story of how life and environments changed,” Tice recently said in a statement issued by Texas A&M. “Finding organics stored in similar ways on Mars tells us that there could be similar stories preserved there as well.”

The findings also suggest that Martian rocks may contain evidence from a time before life began, a record of sorts that Earth’s past geology has mostly erased.

“It is even possible that some Mars rocks will tell us about times when there was no life there,” he said, with organics formed instead through prebiotic chemistry or delivered from space. “We do not have an equivalent record of such a time preserved on Earth.”

The findings build on earlier research by Tice and his team that identified possible biosignatures in Mars rocks studied by NASA’s Perseverance rover. 

Tice suggests, “When we looked even closer, we saw things that are easy to explain with early Martian life but very difficult to explain with only geological processes.”

The rocks contained organic carbon and key elements connected to microbial energy sources, along with chemical patterns that may show redox reactions (processes often associated with life on Earth).

“With the right collection, we could find the next step in evidence for past life on Mars or learn about the kinds of processes that eventually led to life on our planet.”

Tice and his colleagues will continue their work exploring the Martian land. 

“I’m continuing to study the record of early Martian evolution as part of the PIXL instrument team on the Perseverance rover,” he said.

“In addition, I’m comparing how organisms affected some of the oldest sediments on Earth — now preserved in rocks in South Africa—with the potential biosignatures we discovered on Mars.”

Additional details about Tice and his team’s work can be found in a pair of papers, “Diverse organic molecules on Mars revealed by the first SAM TMAH experiment,” which appeared in Nature Communications, and “Redox-driven mineral and organic associations in Jezero Crater, Mars,” which was published in the journal Nature.

About 400 million years ago, the population of plants with vein systems for transferring water and nutrients, called vascular land plants, exploded. Soon thereafter, rocks from some continental magmas showed notable shifts in their chemical compositions. Geologists have suggested that these magma changes happened worldwide, but some argue that the data might be biased because some geographic regions have more samples to analyze than others. A new research team recently tested whether these magmatic changes occurred on a global scale, versus in isolated mountain belts or volcanic islands. 

Geologists use the chemistry of rocks formed from magma to understand a magma’s history. In particular, a mineral called zircon that forms from cooling magma preserves chemical clues about where the magma came from and what it interacted with. To test whether magma changes were global or local, the authors needed data ranging from the equator to the poles. Continents have shifted over the past 400 million years, so scientists use the latitude a rock had when it formed, called its paleolatitude, to compare samples from different parts of ancient Earth. To understand magma histories worldwide, the team used publicly available chemical data from zircons in magmatic rocks that formed across a wide spread of paleolatitudes.

Chemical elements with the same number of protons but different numbers of neutrons are called isotopes with different masses. To discern how plants influenced magma, the researchers analyzed 2 different isotope signals preserved in the zircons. The first isotope signal comes from the ratio of the heavy to light oxygen isotopes, which increases when sediment mixes into magma. Scientists refer to this value as δ¹⁸O, pronounced “delta 18-O.” 

The second isotope signal comes from the element hafnium, denoted Hf. Geologists use hafnium to estimate how long ago magmas melted and separated from the mantle. Zircon contains 2 Hf isotopes, one of which is stable and one of which is produced by radioactive decay. Because this decay happens over billions of years, the ratio between the 2 Hf isotopes over time shifts only slightly. Geologists express these tiny differences using a shorthand called εHf, pronounced “epsilon hafnium,” which shows how much a magma’s Hf signature has changed from Earth’s original mantle. Lower εHf values indicate magmas that incorporated older crustal rock, while higher εHf values reflect mantle sources.

The researchers found that δ¹⁸O values increased as εHf values decreased in these zircons. They concluded that this trend indicates increasing amounts of land-derived sediment in magmas, corresponding with the evolution of land plants. They suggested that land plants altered the ancient landscape, changing how sediments weathered and moved over land. 

To explore this pattern in detail, the team focused on the Andes Mountains, a region that preserves a long history of magmatic activity across a long span of space and time. Using a database, they accessed isotope data from zircon samples collected in the Andes Mountains by dozens of other research groups. These samples covered 32 degrees of modern latitude and 520 million years of Earth’s history, offering a broad window into how magma chemistry changed during that time.

They found that zircons older than 450 million years had no relationship between their εHf and δ¹⁸O values. However, in zircons younger than 450 million years, δ¹⁸O increased as εHf decreased. The researchers saw this pattern in magmas that formed along the edge of the continent, where one tectonic plate sinks below the other, called a subduction zone. They also saw this pattern in magmas that formed inland, away from the subduction zone, around 200 million years ago during the breakup of the supercontinent Pangaea.

 They found similar results in published zircon isotope data from igneous rocks in China, the Caribbean, Antarctica, Madagascar, and Tasmania. Zircons from each region showed the same relationship as zircons in the Andes. Since paleolatitude can also reflect ancient climate, the researchers compared the ratio of εHf and δ¹⁸O, written as εHf/δ¹⁸O, with paleolatitude to test whether ancient climate zones influenced magma chemistry. They found no link between paleolatitude and εHf/δ¹⁸O. 

With these results in mind, the researchers concluded that the relationship between εHf and δ¹⁸O shifted worldwide after vascular land plants evolved. They argued that as plants spread across the continents, their roots accelerated the breakdown of rocks. This accelerated weathering produced large amounts of sediment that washed into ocean basins and was eventually subducted into the mantle, forever changing the chemistry of magma formed there. They suggested that this chain of events illustrates how life on Earth’s surface can drive changes deep within the planet. 

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