It is impossible to know the geological history of the formation of our planet, because it has been destroyed by the subsequent tectonic movement and evolution of the Earth’s surface. Or perhaps it is not entirely impossible…
There are very rare clues about this process that may be obtained from pieces of other planets that have arrived on Earth’s surface in the form of meteorites. In particular, Mars may provide an indication of the early evolutionary path of our planet. More than 4.5 billion years ago, Mars may have had a crust similar to that found on early Earth, and the information about this crust may be hiding in the very oldest Martian meteorite currently known to have landed on Earth.
But first, scientists had to identify where exactly the 4.48-billion-year-old meteorite, nicknamed Black Beauty, came from on the surface of Mars. The study, published in Nature Communications, details the methods that the international team used to identify that this piece of Martian rock originated from one of the oldest regions of the surface of Mars.
“This meteorite recorded the first stage of the evolution of Mars and, by extension, of all terrestrial planets, including the Earth,” said Valerie Payré, a postdoctoral researcher in the Department of Astronomy and Planetary Science at Northern Arizona University. “As the Earth lost its old surface mainly due to plate tectonics, observing such settings in extremely ancient terrains on Mars is a rare window into the ancient Earth surface that we lost a long time ago.”
The meteorite, known officially as NWA (Northwest Africa) 7034 for where it was recovered, is composed of a variety of igneous, sedimentary, and impact melt clasts, including the most evolved and oldest igneous clasts and zircons, dated at 4.44–4.48 Ga (billion years), approximately the time of the formation of Mars. Although the scientists know details of its chemical composition, the source region of this unique meteorite on Mars has so far remained unknown. Given its antiquity, it is possible that it is a piece of the planet’s early crust and thus preserves insights into the geological history of the planet.
Previous research, using a crater-detection algorithm and high resolution images of the surface of Mars, had identified only 18 crater sites where asteroid strikes were powerful enough to have hurled NWA 7034 far enough off the Martian surface to enter space and begin its journey to Earth’s surface.
The current research, led by Anthony Lagain from Curtin University in Australia, used the geochemical and geophysical properties of the ancient meteorite, along with its geochronology, to identify which of these craters was the potential origin of this piece of Mars. They found only one candidate – the Karratha crater – which matched the meteorite’s unique combination of magnetic field intensity, high concentrations of potassium and thorium, and dating details. Furthermore, the experts deduced that when the asteroid that formed this crater struck the surface of Mars, it ejected other debris, including NWA 7034, that was lying on the surface as the result of a much earlier collision that had formed the older crater named Khujirt.
Both these craters are found in the region known as Terra Cimmeria-Sirenum, a highland region covering about 10 percent of the planet, where there are high concentrations of the elements potassium and thorium, and a high magnetic field intensity. It is one of the most ancient regions of Mars, considered to represent a block of ancient crust, and this makes it possible that the Black Beauty is actually a piece of the very early geological history of the planet.
“For the first time, we know the geological context of the only brecciated Martian sample available on Earth, 10 years before the NASA’s Mars Sample Return mission is set to send back samples collected by the Perseverance rover currently exploring the Jezero crater,” said Lagain, a research fellow in the School of Earth and Planetary Sciences at Curtin. “This research paved the way to locate the ejection site of other Martian meteorites, in order to create the most exhaustive view of the Red Planet’s geological history.”
Payré studies the nature and formation of Mars’ crust to determine if Earth and Mars share a common past that includes both a continent-like and ocean-like crust. She uses orbital observations captured in this region to investigate whether traces of volcanism similar those found on Iceland exist on Mars.
“As of today, Mars’ crust complexity is not understood, and knowing about the origin of these amazing ancient fragments could lead future rover and spatial missions to explore the Terra Sirenum-Cimmeria region that hides the truth of Mars’ evolution, and perhaps the Earth’s,” said Payré.
“This work paves the road to locate the ejection site of other Martian meteorites that will provide the most exhaustive view of the geological history of Mars and will answer one of the most intriguing questions: why Mars, now dry and cold, evolved so differently from Earth, a flourishing planet for life.”