Olympus Mons on Mars is thought to have formed about 3.5 billion years ago.
NOT BSTOTAL BS
HARDLY BS — Verdict: Mostly True
Verified by Lenz ·
The Short Version
Evidence from USGS and peer-reviewed Mars geology studies supports an origin for Olympus Mons around 3.5 billion years ago, more broadly about 3.5 to 3.7 billion years ago. The claim matches the accepted estimate for when the volcano began forming. The main caveat is that Olympus Mons continued growing and resurfacing for billions of years afterward.
Caveats
The date refers to the onset of formation or main early construction, not the age of every lava flow on the volcano.
Olympus Mons remained volcanically active long after its initial formation, with some surface units much younger than 3.5 billion years.
Popular or aggregated sources can mix initial edifice age with later resurfacing ages; Olympus Mons-specific geologic studies are the more reliable basis.