Earth and Mars are very much alike, but also very different. Among other things, scientists find that Earth is much more mineral-rich than the Red Planet. It has 6,000 different minerals. By contrast, Mars has only 161. That’s a big difference. How could this have happened?
A new paper in the Journal of Geophysical Research-Planets points to several reasons why the difference exists. According to a team led by Robert M. Hazen of the Carnegie Institution for Science, at least two events influenced Earth’s mineral diversity: plate tectonics and the rise of life. Mars didn’t experience those, at least not that we know of, so that could explain why it shows so few minerals on its surface.
The creation and formation of minerals on these two worlds really began before the Solar System formed. Hazen and others estimated that there were perhaps a dozen available at that time. They were things like diamond and graphite, carbides, nitrides, oxides, and magnesium silicates likely in the protosolar nebula.
Artist’s impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Those early particles brought primitive minerals to each world. Credit: NASA/JPL-Caltech
In the era when planets accreted, primary achondrites were the building materials of choice. Collisions between planetesimals forced further changes. The mineral evolution on Earth and Mars began during this period, which began some 4.56 billion years ago. During what Hazen and others call the “Era of Crust and Mantle Reworking”, the worlds went through phases where igneous (volcanic) activity dominated. It’s very likely the first minerals on both planets crystallized directly from cooling magma. Hydrothermal activity probably also led to new ones in both worlds. Later mineral-forming sequences followed. Those created granite and other rocks.
Hydrothermal activity likely also led to many new minerals on each planet. However, Earth’s array went through extensive stages of diversification billions of years ago with the onset of plate tectonics around 3 billion years ago and the proliferation of life (which began some 3.8 billion years ago). Neither process is known to have occurred on Mars. So, the two worlds diverged and went on separate evolutionary tracks.
According to the team’s paper, the earliest Mars minerals formed as they did on Earth. That is, they began as mafic igneous rocks. Over time, crystals formed as basaltic igneous rocks found their way through the ground. Others formed as primary minerals precipitated from water (presumably in seas and lakes), as well as from hydrothermal and weathering processes.
An artistic conception of the early Earth, showing a surface pummeled by a large impact, resulting in the extrusion of deep-seated magma onto the surface. Formation of additional minerals began at this time, probably on Mars as well. At the same time, distal portion of Earth’s surface could have retained liquid water. Credit: Simone Marchi
Hydrothermal mineral formation was likely also associated with both volcanic fluids and activity in impact fracture zones. Impactors slammed into the planet, which created the fracture zones and forced mineral creation. Both activities probably triggered significant mineral diversification. The paper abstract states, “At least 65 such primary minerals have been identified by flown missions to Mars and from Martian meteorites.”
Near-surface processes related to water/rock interactions in lakes, oceans, and streams created other secondary Mars minerals. For example, boron deposits exist on Mars which was likely present in groundwater that once flowed in Gale Crater.
Rocks also experienced oxidation and reduction, chemical processing, and other alterations as chemicals were lost from the original surface materials. There is also evidence for metamorphic rocks (those formed under extremes of pressure and temperature), including thermal (presumably volcanic-induced as well as impact-related) and shock metamorphism, lightning, and bolide impacts. However, unless something surprising shows up from beneath the surface, the lack of plate tectonics on Mars points away from that as a major pathway for mineral formation on the Red Planet.
The ongoing exploration of Mars began more than half a century ago. Orbiters, landers, mappers, and rovers provide the most compelling evidence of Mars’s topography and elemental abundances. But, we also have Martian meteorites that land on Earth. They reveal more detailed “first-hand” information about the rocks on Mars. This is largely how scientists know of at least 161 confirmed or likely minerals on the Red Planet. They exist in diverse phases, including primary igneous, sedimentary, and near-surface metamorphic rocks. Of course, our knowledge is limited largely to surface rocks. There aren’t a lot of samples of rocks from beneath the surface, yet.
Even though early Mars was probably warmer and wetter for a time, it didn’t experience the same kinds of activities that formed the huge diversity of minerals on Earth. Yes, Mars volcanism happened. We see evidence in its array of volcanoes, for one thing. Yes, there was water on Mars and that played a role in processing rocks and minerals. But, here at home, mineral diversity also depends on plate tectonics forcing of element concentrations, and regional metamorphism (which builds mountains, for example).
And, that’s even before we get to biomineralization. That’s where living organisms produce minerals. Think of organisms that form shells or internal skeletons (like our bones). Or, in larger terms, consider limestone, which is calcium carbonate. It can form naturally when the minerals calcite and aragonite precipitate out of water. However, limestone forms when accumulations of corals and shells create layers in sea bottoms. Eventually, those harden into layers of rock. That doesn’t appear to have happened on Mars.
So, the conclusion is that mineral formation on Mars and Earth followed different pathways once the initial stages of planetary formation were past. Hazen and the team suggest that, based on current knowledge, the total count of Martian minerals is likely to be an order of magnitude smaller than Earth’s. This is based on knowledge of Mars’s history. Based on current observations and past studies, the team found only 20 primary and secondary modes of mineral formation on Mars. Earth has at least 57, and that likely explains the big differences between both worlds.
Research Suggests Mars Has Far Fewer Minerals than Earth
On the Diversity and Formation Modes of Martian Minerals
Mineral Evolution: Mineralogy in the Fourth Dimension
