Before we discuss the geological eras of the planet Mars we will first talk about the formation of all our planets, and the formation of our solar system.
More than 4.6 billion years ago, there wasn’t a Solar System. Instead, there was only a cloud of cold molecular gas and dust light years across. Some event, like a nearby supernova explosion, caused the solar nebula to collapse, creating regions of higher density. In these dense regions gravity took over, pulling material inward into dense pockets where stars would eventually form.
In just one of these regions of the solar nebula is where our entire Solar System began to form. As the nebula collapsed it began to spin up, conserving the momentum of all the individual atoms in the cloud. Most of the material collected together into a ball in the center, but some spun out into a flattened disk around the newly forming Sun.
Recently a different theory was published, that explains the forming of our Sun and our planets at the same time. Not the Sun first and then the planets.
Using classical physics, the laws of thermodynamics and mechanics, Anne Hofmeister and Robert Criss (Washington University in St. Louis) present an accretion model that assumes a pre-solar nebula collapsed and formed the Sun and planets at essentially the same time, with the planets contracting toward the Sun. The temperature is cold, not hot.
Rocky kernels are formed and the nebula starts contracting. The Rocky kernels form to conserve angular momentum and they attract dust and gas. But to do that they have to compete with the gravitational pull of the Sun. So only rocky kernels that are far from the Sun, like Jupiter and further planets, can out-compete our Sun. Mercury, Venus, Earth and Mars are too close to the Sun. This gravitational competition gives us the regularity, spacing, and graded composition of our Solar System. This theory of gravitational competition also offers a new view on the formation of the moon, as with gravitational competition our Moon will be formed without a giant impact, which many scientist feel has a low probability of having occurred at all.
Back to the comparison of Earth, Venus and Mars:
Earth and Venus in contrast to Mars are larger planets with substantial internal heat sources and significant atmospheres. Earth’s surface is continually reshaped by tectonic plates sliding under and against each other and by materials spouting forth from active volcanoes where plates are ripped apart. The Earth map we consider ‘normal’ is only been drifting to its present shape for 180 million years.
Both Earth and Venus have been paved over so recently that both lack any visible record of cratering from the era of bombardment in the early solar system.
Here are certain things to look out for while moving through time in this animation. We begin at 150 million years ago, when the Seychelles were still buried within the Gondwana supercontinent. Note that present-day coastlines are outlined in purple, while green areas represent land either above or below sea level. As Gondwana breaks up, watch for the birth of the Mascarene Platform, on which the Seychelles lie, about 65 million years ago. Observe India as it collides with Asia, leaving behind the so-called 90 East Ridge. Represented by the green line appearing to jut out of eastern India, the 90 East Ridge is a submerged mountain range that arose along a hotspot trail (much as the Hawaiian islands did). The animation continues 50 million years into the future, with the African Rift Valley opening up widely and India migrating well into Asia. Please note that these future projections are purely speculative and merely represent how tectonic-plate movements are currently trending.
The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like (visco-elastic solid) asthenosphere. Plate motions range up to a typical 10–40 mm/a (Mid-Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/a (Nazca Plate; about as fast as hair grows)
The driving force of plate tectonics is now thought to be plume tectonics, a theory developed during the 1990s. This theory is a modified concept of mantle convection currents is used, related to super plumes rising from the deeper mantle which would be the drivers or the substitutes of the major convection cells. We see no evidence of plate tectonics on Mars. Ofcourse we might be wrong, with science of Mars we have been updating our theories a lot over the last 35 years.
Planetary scientists do agree that the terrestrial planets formed very quickly within the first 50-100 million years of the solar system’s history (4,600-4,500 million years ago). There is some debate as to whether our Moon formed from an impact between a Mars-sized object and the proto-Earth at some point during that time, or not. What we know is that we have a moon, and that it plays part in the tides or our Earth.
About 3,800 million years ago the Late Heavy Bombardment happened. At that time a large number of impact craters formed on the Moon within a time span of only seventy million years — and based on observations of our Moon the planets Earth, Mercury, Venus, and Mars were likely pummelled by impacts as well.
There is quite some debate about why Mars is no bigger than she is. One of the theories is that Mars might be only a small planet, because when it was an embryo planet growing to become mars sized, gobbling up other planetesimals, it drifted out of the zone where all the material for planet growth was hanging around. Mars moved through the solar system disk away from this building material and so Mars’ growth got stalled at its current size. And Mars is small: at only 6,792 km across, it’s about half the diameter of Earth, and has only 10% of the Earth’s mass.
Mercury and our Moon, lacking an atmospheres, are riddled with craters that are relics of impacts from a period of bombardment when the inner planets were sweeping up remnants of small rocky bodies that failed to “make it as planets” in the solar system’s early times.
Be that as it may, what we do know is that Mars appears to stand between the rocky worlds like Earth and Venus and the gas giants.
Like Earth and Venus, it possesses many volcanoes, and there is ongoing debate as to when, even if, volcanic activity stopped on Mars.
On Earth, a single “hot spot” or plume might form a chain of middling-size islands, such as the Hawaiian Islands, as a tectonic plate slowly slides over it. On Mars, there are apparently no such tectonic plates, at least as far as we know today. An idea that seems to be supported by the fact that the volcanoes on Mars are enormous. When volcanoes formed in place they had the time to become much more enormous than the rapidly moving volcanoes on Earth. Overall, Mars appears to be neither as dead as Mercury and our moon, nor as active as Earth and Venus.
Based on what we have learned from spacecraft missions, scientists view Mars as the “in-between” planet of the inner solar system. Small rocky planetary bodies such as Mercury and Earth’s moon apparently did not have enough internal heat to drive the motion of tectonic plates, so their crusts grew cold and static relatively soon after they formed when the solar system condensed into planets about 4,600 million years (4.6 billion years) ago.
Thanks to the ongoing observations by current Mars missions, our theories about Mars are still evolving.
Mars almost resembles two different worlds that have been glued together. From latitudes around the equator to the south are ancient highlands pockmarked with craters from the solar system’s early era, yet riddled with channels that attest to the flow of water. The northern third of the planet, however, overall is sunken and much smoother at kilometer (mile) scales.
Analysis of subsurface densities by their gravitational effect on orbiters supports a theory that an impactor almost big enough to be a planet itself bashed Mars early in Martian history, excavating the largest crater in the solar system. But even if that happened, it was long-enough ago that it would not explain the smoothness of the northern plains. As there still should be many more impact craters visible than there are.
Theories for that range from proposing that the plains are the floor of an ancient sea to proposing that the smoothness is merely the end product of innumerable lava flows.
Studies of impact crater densities on the Martian surface allow us to identify 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:
**The Noachian Era (named after Noachis Terra) spanned roughly the first 1,000 million years of Mars’ existence after the planet was formed 4,600 million years ago. It saw the 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. In this era, scientists suspect that Mars was quite active with periods of warm and wet environments, erupting volcanoes and some degree of tectonic activity. The Tharsis bulge is thought o have formed during this period, with extensive flooding by liquid water late in the epoch. The planet may have had a thicker atmosphere to support flowing water, and it may have rained and snowed.
** The 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.
These lava plains formed between 3,500 to 2,000 million years ago. But their formation might have lasted only 500 million years, thus until 3,000 million years ago. In this era geologic activity was slowing down and near-surface water perhaps was freezing to form surface and buried ice masses. Despite plunging temperatures, water pooled underground erupted when heated by impacts. This caused the catastrophic floods that surged across vast stretches of the surface — floods so powerful that they unleashed the force of thousands of Mississippi Rivers. Eventually, water became locked up as permafrost or subsurface ice, or was partially lost into outer space.
**The Amazonian epoch (named after Amazonis Planitia) lasted from 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.
As the Hesperian may have lasted until 3,000 million OR 2,000 million years ago, it is not completely certain when the Amazonian era started.
The planet is now a dry, desiccating environment with only a modest atmosphere in relation to Earth. In fact, the atmosphere is very thin, which also means that the atmospheric pressure on Mars is extremely low: 6-35 millibars depending on the warmth of the atmosphere and the amount of dust present in the atmosphere. This low pressure / thin atmosphere makes it impossible for pure water to exist in liquid form on the surface of Mars. The moment water is exposed to it the atmosphere it becomes a gas, unless the water is too cold to be anything more than water ice.
This dating of Mars, based on the number of craters showing on a Mars surface 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.
There is another assumption, that might be proven wrong, that Mars has no active volcanism in at least the last 2,000 million years. However scientists believe they are seeying young lava flows (dating in the last 10 million years), which might throw this whole idea of ’crater counting to know how old a region in Mars’ is overboard.
Also as Mars has a wobble due to a lack of a big moon to keep her stable while spinning around her axes, the climate and perhaps the stability of water at the surface may vary on scales of thousands to millions of years as the tilt of the planet and its distance from the sun change cyclically.
As we already stated above the theories around Mars evolve based on what science data our mars mission brings us. 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 strong relation between the mineralogy and geology of the planet.
This proposed timeline also divides the history of the planet into 3 epochs:
*** Phyllocian (named after the clay-rich phyllosilicate minerals that characterize the epoch) lasted from the formation of the planet until around 4,000 million years ago. In order for the phyllosilicates to form the water environment would have been alkaline. 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.
Phyllosilicates are theminerals that are composed of sheets. Chemical bonding is strong within the sheets and weak between them, making the sheets breaking off from each other quite easily. The group contains serpentines, micas(muscovite, biotite etc) and clay minerals (kaolinite, illite, montmorillonite etc).
*** Theiikian (named, in Greek, after the sulfate minerals that were formed), lasting until about 3500 million years ago, was a period of volcanic activity. Besides lava many gasses – and in particular sulfur dioxide – were released. Those gasses combined with water to create sulfates and an overal acidic environment. The equivalent on earth is the eoarchean era and the beginning of the paleoarchean era.
Gypsum forms bladed concretions called desert roses or sand roses, growing in sediments that are subjected to concentrated brines. The crystals grow from a central point, and the roses emerge when the matrix weathers away.
*** 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. Hematite is the mineral form of iron(III) oxide (Fe2O3), one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of Mars. Maghemite is a hematite- and magnetite-related oxide mineral. The equivalent on earth is most of the archean all of the proterozoic and up to now.
Apart from that broad outline of the eras on Mars, there is a very lively debate and lots of disagreement on the details of Mars’ history.
How wet was the planet, and how long ago? What eventually happened to all of the water? That is all a story that is still being written.
Even if we ultimately learn that Mars never harbored life as we know it here on Earth, scientific exploration of the Red Planet can assist in understanding the history and evolution of life on our own world.
Much if not all of the evidence for the origin of life here on Earth has been obliterated by the rapid pace of weathering and global tectonics that have operated over billions of years. Mars, by comparison, is a composite world with some regions that may have histories similar to Earth’s ancient crust, while others are a frozen gallery of the solar system’s early days.
Thus, even if life never developed on Mars — something that we cannot answer just yet — scientific exploration of the planet may yield critical information, unobtainable by any other means, about the pre-biotic chemistry that led to life on Earth. Mars as a fossil graveyard of the chemical conditions that fostered life on Earth is an intriguing possibility.