Geologic Time Scales on Earth, Mars, and the Moon

Released to the public domain 2007 by Thomas Gangale

Comparing the geological time scales of Earth and Mars brings into stark focus how little has happened on Mars in the last two or three billion years. It is thought that the last time there was abundant liquid water on Mars was during the Noachian epoch, which ended 3.5 billion years ago. It is supposed that the simplest life-forms may have evolved on Earth about four billion years ago; however, life on Earth didn't get interesting until the "Cambrian explosion," about 500 million years ago, when most of the phyla extant today evolved. Nevertheless, in the window 4.0 to 3.5 billion years ago, it is possible that life got started on Mars. If so, how long it may have persisted is an open question, but unquestionably it would be very simple. Current evidence suggests that the last universal common ancestor of terrestrial life, a single-celled organism, lived during the early Archean eon, perhaps roughly 3.5 billion years ago.

The time scale graphics are adapted from Wikipedia.

The following text is taken from Wikipedia and is in the public domain.

Crater density timeline

Studies of impact crater densities on the Martian surface allow us to identify has three broad epochs in the planet's geological timescale, as older surfaces have more craters and younger ones less. The epochs were named after places on Mars that belong to those time periods. The precise timing of these periods is not known because there are several competing models describing the rate of meteor fall on Mars, so the dates given here are approximate. From oldest to youngest, the time periods are:

  • Noachian epoch (named after Noachis Terra): Formation of the oldest extant surfaces of Mars between 3800 and 3500 million years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge is thought to have formed during this period, with extensive flooding by liquid water late in the epoch.

  • Hesperian epoch (named after Hesperia Planum): 3500 million years ago to 1800 million years ago. The Hesperian epoch is marked by the formation of extensive lava plains.

  • Amazonian epoch (named after Amazonis Planitia): 1800 million years ago to present. Amazonian regions have few meteorite impact craters but are otherwise quite varied. Olympus Mons formed during this period along with lava flows elsewhere on Mars.

The studying of craters is based upon the assumption that crater-forming impactors have hit the planet all throughout history at regular intervals, and there is no way to exactly date an area just based upon the number of impacts, only to guess that areas with more impacts must be older than areas with fewer impacts. For example this system of logic breaks down if a large number of asteroids had hit at once, or if there were long periods where few asteroids hit.

Mineralogical timeline

Based on recent observations made by the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter, the principal investigator of the OMEGA spectrometer has proposed an alternative timeline based upon the correlation between the mineralogy and geology of the planet. This proposed timeline divides the history of the planet into 3 epochs; the Phyllocian, Theiikian and Siderikan.

  • Phyllocian (named after the clay-rich phyllosilicate minerals that characterize the epoch) lasted from the formation of the planet until around 4000 million years ago. In order for the phyllosilicates to form an alkaline water environment would have been present. It is thought that deposits from this era are the best candidates to search for evidence of past life on the planet. The equivalent on Earth is much of the hadean eon.

  • Theiikian (named, in Greek, after the sulfate minerals that were formed), lasting until about 3500 million years ago, was a period of volcanic activity. In addition to lava, gasses - and in particular sulfur dioxide - were released, combining with water to create sulfates and an acidic environment. The equivalent on Earth is the eoarchean era and the beginning of the paleoarchean era.

  • Siderikan, from 3500 million years ago until the present. With the end of volcanism and the absence of liquid water, the most notable geological process has been the oxidation of the iron-rich rocks by atmospheric peroxides, leading to the red iron oxides that give the planet its familiar color. The equivalent on Earth is most of the archean all of the proterozoic and up to now.