when did olympus mons form

Olympus Mons did not form at one single moment, but most estimates place its main growth between about 3.8–3.0 billion years ago, early in Mars’ history, with some volcanic activity possibly continuing much later.

Quick Scoop: When did Olympus Mons form?

• Many planetary scientists link its origin to the late Noachian / early Hesperian periods, roughly around 3.5–3.0 billion years ago.

• Some sources describe it as forming “several billion years ago” as Mars’ interior was hotter and volcanism much more vigorous than today.

• Crater counts and lava flow ages suggest Olympus Mons is actually one of the younger giant volcanoes on Mars, even though it is still billions of years old.

• Evidence from calderas and lava plains implies that smaller eruptions may have continued into the Amazonian period, possibly as recent as a few hundred million years ago.

So in plain terms: Olympus Mons began forming very early in Mars’ history, over 3 billion years ago, but it likely took a long time to reach its enormous size, with volcanism tapering off gradually rather than stopping all at once.

TL;DR: When did Olympus Mons form?
Mainly in the early to mid history of Mars (roughly ~3.5 billion years ago), with its giant shield built over a long span of volcanic eruptions and some later activity that may have persisted into comparatively recent geological times.

Information gathered from public forums or data available on the internet and portrayed here.