Sciency Words: Geologic Periods of Mars

One of the reasons I write this Sciency Words series is to introduce you to terms that I know (or at least suspect) we’ll be talking about in upcoming blog posts. Right now, I’m just getting started with my special mission to Mars series, so I think this is a good time to introduce you to not one but four interesting scientific terms.

Today, we’re looking at the four major periods of Mars’s geological history (based primarily on this article from ESA and this article from the Planetary Society).

PRE-NOACHIAN MARS (4.5 to 4.1 billion years ago)

This would have been the period when Mars, along with the rest of the Solar System, was still forming.

NOACHIAN MARS (4.1 to 3.7 billion years ago)

This period was characterized by heavy asteroid/comet bombardment, as well as plenty of volcanic activity. Most of the major surface features we see today formed during this time: the Tharsis Bulge, Valles Marineris, several of the prominent impact basins in the southern hemisphere, and also the vast northern lowlands—or would it have been the northern oceans? Also valley networks that formed during this time look suspiciously like river channels.

HESPERIAN MARS (3.7 to 3.0ish billion years ago)

Around 3.7 billion years ago, it seems asteroid and comet impacts on Mars died down, and volcanic activity kicked it up a notch. We also see a lot of surface features called “outflow channels” corresponding to this time, rather than the river-like valleys that appeared during the Noachian. These outflow channels may have been created by sudden and violent floods, which may have been caused by melting ice dams releasing lake water.

AMAZONIAN MARS (3.0ish billion years ago to today)

The Amazonian Period began when the northern lowlands, specifically a region called Amazonis Planitia, was “resurfaced,” covering up any impact craters or other surface features that may have been there before. Mars experts disagree about when this happened, but most estimates seem to be in the neighborhood of three billion years ago. Any obvious volcanic or geologic activity ceased during the Amazonian, and for the most part all of Mars’s water has either frozen solid or evaporated into space.

On Earth, if you want to talk about the age of the dinosaurs, what you’re really talking about is the Mesozoic Era, which is subdivided into the familiar Triassic, Jurassic, and Cretaceous Periods. And so if you’re looking for dinosaur fossils, you need look for Mesozoic Era rocks.

At this point we only have a rough sketch of the geologic history of Mars. We don’t know enough to make the kinds of divisions and subdivisions that we’ve made for Earth. But if you want to go looking for Martian dinosaurs (by which I mean fossilized Martian life of any kind, even if its only microbial) then I can tell this much: look for Noachian and Hesperian aged rock formations. Those are the rocks that would have formed back when Mars still had oceans and lakes and rivers (or at least random, violent floods).

At least, landing near some Noachian and/or Hesperian rocks seems to be a high priority for NASA’s Mars 2020 rover.

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