Sciency Words: Geologic Periods of Mars

November 3, 2017

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.

Sciency Words: Holocene (An A to Z Challenge Post)

April 10, 2017

Today’s post is a special A to Z Challenge edition of Sciency Words, an ongoing series here on Planet Pailly where we take a look at some interesting science or science related term so we can all expand our scientific vocabularies together. In today’s post, H is for:


Real dinosaur fans can tell you that dinosaurs lived in the Mesozoic Era, a geological era that is subdivided into the Triassic, Jurassic, and Cretaceous Periods.

Real fans of humans can tell you that humans live in the Cenozoic Era, in a subdivision called the Quaternary Period, in a further subdivision known as the Holocene Epoch—a name which can be translated from Greek to mean “entirely recently.” Again, scientists, you can be more creative than that.

This “entirely recent” epoch began approximately 11,700 years ago, a time which corresponds loosely to the end of the most recent ice age and also corresponds loosely to what archeologists call the mid to late Stone Age.

Major developments during the Holocene include melting glaciers, the extinction of animals like the woolly mammoth and saber-toothed tiger, and of course the rise and spread of human civilization.

The Holocene ends with… well, obviously we don’t know how it ends. Or maybe we do.

There’s an ongoing debate among geologists about whether or not the Holocene has ended already. Some say a new geological epoch—called the Anthropocene—has begun. Anthropocene is derived from the Greek word for human, and it would be characterized by the effects human activities are having on the geology of this planet.

The International Commission on Stratigraphy is in charge of naming geological time periods and defining their start and end points, and the I.C.S. has a working group studying the Holocene vs. Anthropocene issue.

If the Anthropocene is accepted as an official geological epoch by the I.C.S., then the Holocene may have ended about two hundred years ago with the beginning of the Industrial Revolution. There’s an alternative proposal that would have the Holocene end in the mid-20th Century with the dawn of the nuclear age, because changing levels of radioisotopes in rock strata would make the boundary between the two epochs easier to identify. And there’s a proposal to make the Anthropocene a subdivision within the Holocene, rather than making it its own separate epoch.

Whatever the I.C.S. decides to do, their decision will probably be controversial. But it won’t be the first time an international organization like this stirred up controversy over how to define scientific terms. More on that tomorrow.