After analyzing some of the oldest Martian material, an international team of researchers suggest that the crust of the Red Planet was in place no later than 4,547 million years ago. This implies that Mars formed extremely quickly and that habitable conditions might have existed on Mars 100 million years before they did on our own planet.
As reported in Nature, the researchers used zircons from Martian meteorites to establish the geological timestamps. The team dated them to between 4,430 and 4,476 million years ago, forming roughly 90 million years after the crust formed. In less than 20 million years, Mars went from a magma ocean into a solid crust, according to the team. This crust was then reworked, possibly by impacts, at the time of the zircons' formation.
This study has many implications for Mars and the formation of rocky planets in general. If the crust truly solidified so quickly, the mantle might not have had time to mix well. The researchers think that this would have created very specific types of crust, a fact they use in their zircon formation model.
This scenario also has strong implications for the quick formation of rocky planets. It is estimated that the first solid pebbles formed in the young Solar System about 4,567 million years ago. This research suggests that it took Mars just 20 million years to go from stardust to solid planet with a crust. Definitely a quick-turnaround but one that is predicted in the pebble accretion model.
This model claims that planets don’t grow by merging with similar-sized objects but by the continuing accretion of small pebbles. To form Mars, it takes only 5 million years, according to this model. This finding goes against several studies that suggest Mars had a prolonged magma ocean phase. However, the team is pretty confident in the zircon data.
Zircons are sturdy minerals that are resistant to wear and corrosion. They are common in igneous rocks, those that form from magma or lava, which is ideal for such a study. Another characteristic also makes zircon useful: They accept certain elements like uranium and hafnium and reject lead.
The rejection of lead is particularly relevant for this study. As zircon forms, lead atoms can’t find a way in, but Uranium can. Uranium decays into lead over billions of years, so all the lead in there must have come from the Uranium – a great way to put a timestamp on the formation. The hafnium, instead, provide evidence for how they formed. There is too little in these zircons if they formed directly from magma, so they more likely formed from a solid crust that melted again.