The Hunt for Ancient Organic Matter on Earth and Mars
How ancient soils preserve organic matter for billions of years and what this means for the search for life on Mars through astropedology.
Explore the ResearchImagine a paleontologist, not brushing dust from a dinosaur bone, but from a chunk of mud as old as the dinosaurs themselves. This mud isn't just old dirt; it's a fossilized soil, or paleosol, a time capsule preserving the chemical whispers of a long-vanished world.
The study of ancient soils on Earth and other planets, a field called astropedology, is revolutionizing our search for the ultimate treasure: signs of life, both here and in the cosmos 1 5 .
For decades, the prevailing wisdom was that organic matter—the carbon-based building blocks of life—decays and vanishes over millions of years. But we now know this isn't the whole story. Under the right conditions, organic carbon can be preserved for billions of years, trapped within the mineral fabric of the planet.
Unlocking the secrets of organic preservation rewrites chapters of Earth's history.
Provides a treasure map for where to look for signs of past life on the Red Planet 1 .
A soil is more than just dirt; it is a dynamic interface where the atmosphere, hydrosphere, and biosphere meet. When buried by volcanic ash, sediments, or lava flows, a soil can be removed from these influences and become a paleosol 1 .
Some of the oldest fossils in terrestrial environments are found not in classic sedimentary rock, but preserved within these ancient soils 1 .
Dynamic interface where atmosphere, hydrosphere, and biosphere interact.
Buried by volcanic ash, sediments, or lava flows, removing it from surface influences.
Becomes a fossilized soil preserving ancient climate, atmosphere, and biological information 1 .
Organic matter is constantly under attack. Microbes seek to consume it for energy, and environmental conditions can break it down. So, how does anything survive over geological timescales? Research points to a complex interplay of factors, but a few are critical.
To understand what might happen to organic matter on Mars, scientists don't always look to the stars—they go to the most Mars-like place on Earth: the Atacama Desert in Chile. Its hyperarid conditions, intense UV radiation, and salt-rich soils provide a perfect natural laboratory.
The MGS-1 Mars regolith simulant proved to be the most effective preservative. It was the only substrate in which degradation products of chlorophyll-a could still be detected after two months of exposure 3 .
The researchers built custom-designed exposure plates with quartz glass covers to allow environmental exposure while protecting samples from wind and new microbial contamination 3 . They then embedded three types of biosignatures into different Mars-relevant substrates:
The universal energy currency of life on Earth.
The key pigment for photosynthesis.
A hardy cyanobacterium known to survive extremes.
The experiment yielded clear and striking results:
| Observation | Result | Implication |
|---|---|---|
| Rapid Biomarker Loss | Green color of cyanobacteria and chlorophyll-a disappeared within two months | Visible signs of organic matter degrade quickly in extreme environments |
| ATP Breakdown | ATP concentrations gradually decreased over time | Degradation rates influenced by substrate and salt type |
| The Mineral Guardian | MGS-1 Mars simulant was the most effective preservative | Right mineral matrix can significantly slow degradation |
| Substrate | Pheophytin-a | Pyropheophytin-a |
|---|---|---|
| Quartz | No | No |
| Quartz + Chloride | No | No |
| Quartz + Perchlorate | No | No |
| Gypsum | No | No |
| MGS-1 Mars Simulant | Yes | Yes |
Source: Adapted from 3
Source: Adapted from 3 . Note: Gypsum samples showed inconsistent quantification due to analytical interference.
What does it take to run these experiments? Here are some of the key materials used in the Atacama study and their functions.
| Reagent | Function in the Experiment |
|---|---|
| MGS-1 Mars Regolith Simulant | A laboratory-created analog that mimics the chemical and physical properties of Martian soil, allowing for realistic testing on Earth. |
| Sodium Perchlorate (NaClOâ‚„) | A Mars-relevant oxidant salt known to exist in Martian soil; it challenges organic matter preservation and complicates detection. |
| Chroococcidiopsis (Cyanobacterium) | A model extremophile organism used to test the preservation of a whole microbial cell, not just individual molecules. |
| Adenosine Triphosphate (ATP) | A labile (easily degraded) biomolecule used to gauge the preservation potential for the most fragile biosignatures. |
| Chlorophyll-a | A complex organic pigment used to study the degradation pathways of larger, more complex biomolecules. |
A 2025 study showed that certain plant and microbial carbohydrates can form microscopic "bridges" with clay minerals like smectite, trapping water molecules tightly within the soil structure 8 . This suggests a mechanism for how moisture could have been retained in ancient Martian soils.
The insights from Earth's paleosols and analog experiments like the one in the Atacama are directly shaping current and future missions to Mars.
The Curiosity and Perseverance rovers are equipped to identify mineralogical contexts favorable for preservation. Findings emphasize seeking out clay-rich, reduced layers in subaerial paleoenvironments 1 .
The same prioritization is guiding the selection of samples for the eventual Mars Sample Return mission. Bringing back material from promising paleosol-like units could provide the best chance of finding evidence of past life 1 .
The quest to understand organic matter preservation is more than an academic exercise; it is a journey to the frontiers of life's resilience. By deciphering the conditions that allow life's fingerprints to endure in Earth's most ancient soils, we arm ourselves with the knowledge to probe the mysteries of our neighboring planet.