We've never seen anything like that on Earth
That astronomical understatement came from Marc Caffee, professor of physics and astronomy at Purdue University, who was describing the result of a new study which determined Mars once had a massive volcano that erupted continuously for 2 billion of the planet’s 4.5 billion-year history. Ironically, the key to this discovery was found not on Mars but on Earth.
Even though we've never had astronauts walk on Mars, we still have pieces of the Martian surface to study, thanks to these meteorites.
There are some 100 meteorites on Earth that have been identified as originating on Mars. According to his study published in the journal Science Advances, Chaffee analyzed 30 of them and was able to sort them by age after determining how long they had been exposed to cosmic rays. Eleven of the meteorites appeared to have been formed by cooling magma from the same volcano and were ejected from the Martian surface by the same event, but one of them was surprisingly much older than the rest … nearly 2 billion years older.
What this means is that for 2 billion years there's been sort of a steady plume of magma in one location on the surface of Mars. We don't have anything like that on Earth, where something is that stable for 2 billion years at a specific location.
The largest and best known volcano on Mars is Olympus Mons, which is nearly 17 miles high and would cover all of Arizona or most of France. Until a rover or humans get to Olympus Mons, there’s no way to determine if some of its rocks successfully traveled to Earth, but it’s a possibility.
That uncertainty doesn’t seem to bother Marc Caffee.
These meteorites are allowing us to conduct geologic science on the surface of Mars, and we haven't even been there yet.