Researchers studying a Martian meteorite have uncovered the oldest known evidence of water on Mars, dating back 4.45 billion years.
This finding suggests that Mars’ geological history includes significant hydrothermal activity that could have supported habitability early in the planet’s history. These ancient zircons, analyzed for their trace elements, hint at conditions that might have allowed for the formation of ore deposits similar to those found on Earth, raising fascinating possibilities about Mars’ past.
Earth’s Ancient Waters
Water is everywhere on Earth — covering about 70% of its surface, filling the air, and even locked inside rocks. Geologic evidence shows that water has been a stable presence on our planet for around 4.3 billion years.
Mars, however, tells a different story. The timeline of water on the Red Planet remains uncertain. Scientists are working to determine when water first appeared on Mars, where it was concentrated, and how long it lasted. If Mars was ever habitable, it would have required at least some water.
In a breakthrough study, we analyzed the mineral zircon in a Martian meteorite and discovered evidence of water dating back 4.45 billion years. These findings, recently published in Science Advances, may be the oldest evidence yet of water on Mars.
A Wet Red Planet
Water has long been recognized to have played an important role in early Martian history. To place our results in a broader context, let’s first consider what “early Mars” means in terms of the Martian geological timescale, and then consider the different ways to look for water on Mars.
Like Earth, Mars formed about 4.5 billion years ago. The history of Mars has four geological periods. These are the Amazonian (from today back to 3 billion years), the Hesperian (3 billion to 3.7 billion years ago), the Noachian (3.7 billion to 4.1 billion years ago) and the Pre-Noachian (4.1 billion to about 4.5 billion years ago).
Evidence for water on Mars was first reported in the 1970s when NASA’s Mariner 9 spacecraft captured images of river valleys on the Martian surface. Later orbital missions, including Mars Global Surveyor and Mars Express, detected the widespread presence of hydrated clay minerals on the surface. These would have needed water.
The Martian river valleys and clay minerals are mainly found in Noachian terrains, which cover about 45% of Mars. In addition, orbiters also found large flood channels – called outflow channels – in Hesperian terrains. These suggest the short-lived presence of water on the surface, perhaps from groundwater release.
Most reports of water on Mars are in materials or terrains older than 3 billion years. More recent than that, there isn’t much evidence for stable liquid water on Mars.
But what about during the Pre-Noachian? When did water first show up on Mars?
Hunting Water on Ancient Mars
There are three ways to hunt for water on Mars. The first is using observations of the surface made by orbiting spacecraft. The second is using ground-based observations such as those taken by Mars rovers.
The third way is to study Martian meteorites that have landed on Earth, which is what we did.
In fact, the only Pre-Noachian material we have available to study directly is found in meteorites from Mars. A small number of all meteorites that have landed on Earth have come from our neighboring planet.
Black Beauty: A Martian Window
An even smaller subset of those meteorites, believed to have been ejected from Mars during a single asteroid impact, contain Pre-Noachian material.
The “poster child” of this group is an extraordinary rock called NWA7034, or Black Beauty.
Black Beauty is a famous Martian meteorite made up of broken-up surface material, or regolith. In addition to rock fragments, it contains zircons that formed from 4.48 billion to 4.43 billion years ago. These are the oldest pieces of Mars known.
While studying trace elements in one of these ancient zircons we found evidence of hydrothermal processes – meaning they were exposed to hot water when they formed in the distant past.
The Hydrothermal Mysteries of Martian Zircons
The zircon we studied is 4.45 billion years old. Within it, iron, aluminum, and sodium are preserved in abundance patterns like concentric layers, similar to an onion.
This pattern, called oscillatory zoning, indicates that incorporation of these elements into the zircon occurred during its igneous history, in magma.
The problem is that iron, aluminum, and sodium aren’t normally found in crystalline igneous zircon – so how did these elements end up in the Martian zircon?
Implications for Martian Ore Deposits
The answer is hot water.
In Earth rocks, finding zircon with growth zoning patterns for elements like iron, aluminum, and sodium is rare. One of the only places where it has been described is from Olympic Dam in South Australia, a giant copper, uranium, and gold deposit.
The metals in places like Olympic Dam were concentrated by hydrothermal (hot water) systems moving through rocks during magmatism.
Hydrothermal systems form anywhere that hot water, heated by volcanic plumbing systems, moves through rocks. Spectacular geysers at places like Yellowstone National Park in the United States form when hydrothermal water erupts at Earth’s surface.
Finding a hydrothermal Martian zircon raises the intriguing possibility of ore deposits forming on early Mars.
A Global Martian Ocean?
Previous studies have proposed a wet Pre-Noachian Mars. Unusual oxygen isotope ratios in a 4.43 billion-year-old Martian zircon were previously interpreted as evidence for an early hydrosphere. It has even been suggested that Mars may have had an early global ocean 4.45 billion years ago.
The big picture from our study is that magmatic hydrothermal systems were active during the early formation of Mars’ crust 4.45 billion years ago.
It’s not clear whether this means surface water was stable at this time, but we think it’s possible. What is clear is that the crust of Mars, like Earth, had water shortly after it formed – a necessary ingredient for habitability.
Written by Aaron J. Cavosie, Senior lecturer, School of Earth and Planetary Sciences, Curtin University.
Adapted from an article originally published in The Conversation.
Reference: “Zircon trace element evidence for early hydrothermal activity on Mars” by Jack Gillespie, Aaron J. Cavosie, Denis Fougerouse, Cristiana L. Ciobanu, William D. A. Rickard, David W. Saxey, Gretchen K. Benedix and Phil A. Bland, 22 November 2024, Science Advances.
DOI: 10.1126/sciadv.adq3694
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