I found this article about Mars being covered with Water and found it interesting.
June 13, 2010
Here is the article:
http://www.colorado.edu/news/r/f9b2e81224758e6b422b6bb0735f7098.html
It will be interesting to see how they solve the mystery of why (to my knowledge) all of the sites having clays or other water-modified rocks and minerals are found in the ancient cratered highlands and not in the smooth northern plains
The ocean froze and we see the stuff deposited on top, not the seabed sediments?
That explains very well why the underlying strata is heavily cratered, but covered by the smooth northern basin. Given the Comanche find and the ph at the Phoenix site could we anticipate that the ocean was a neutral or high ph and that there are carbonates down there? Or is that too much of a leap of faith.
There are many processes and environments involved in the formation of carbonates. Until we know more about the type of carbonate involved and the depositional environment, we don't know many of the fine details. It's just one data point, one piece of the jigsaw puzzle.
My take on Comanche is that it is a hydrothermal feature, whci is a whole 'nuther critter from aquatic deposition.
--Bill
There are likely at least two different "oceans" in Mars history. The DiAchille paper, cited in Bobby's post, analyzed valley networks and deltas from the Noachian period (>3.5 billion years ago.) when climatic conditions were very different than today. Some temporary bodies of water (or mud) probably formed much later in the northern hemisphere in association with the hugh outflow channels carved during the Hesperian (maybe 500 to 1,000 million years after the earlier ocean--absolute dates are uncertain). The chemical environments (pH etc.) were likely very different during each.
What's puzzling to me is that an ancient, cratered Noachian surface is preserved at realtively shallow depths in the northern hemisphere, suggesting that the sediment layers from both oceanic events are fairly thin. Mars is such a fascinating enigma.
Tom
Thanks for clarifying, Tim.
I was thinking oceans (plural) in terms of the differing chemistry, areal extent, and climatic conditions under which standing bodies of water may have formed. Given how ancient the dichotomy appears to be, it seems reasonable that the northern lowlands have been the major sink for water throughout Martian history, and as such would have been the location of the true martian "ocean" (ultimate base level) since very early in the Noachian.
Tom
Indeed, we have two near certainties which contradict each other:
(1) Mars *had to* have a lot of water early on and thus, had to have fairly extensive ocean.
(2) But we don't see much of sedimentary rocks.
One crazy-ish idea from me: what if Mars indeed had a lot of water, but it always was mostly solid?
Even here on Earth, with beefy atmosphere (-> greenhouse effect) and higher insolation, we had pretty bad glaciations. At Mars distance, it should have been colder. What if Mars "ocean" was mostly frozen solid, like continuous ice age with only short periods of catastrophic melting and floods, when polar tilt, greenhouse effect and volcanic heat happen to work together?
After billions of years of slow water loss, especially from surface closer to equator, this will give us today outwardly "dirty", but inside pretty "icy" Mars (lots of ancient river/flood valleys, glaciers, lots of permafrost at latitudes +/-40 and up to poles), yet not much of sediments. Sedimentation doesn't happen in solid water, right?
Re "icy" Mars: http://www.uahirise.org/PSP_008809_2215
this glacier(-like?) feature is at 41.3 N.lat. Why is it _white_ in RGB? Was is covered with water frost when this image was taken?
The view from my armchair is that I like your scenario. I suspect a lot of the water related landforms on Mars will turn out to have formed at the bottom of ice sheets, not at the surface.
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Den, I've got two armchairs.
From one, given that solar output has increased by several tens of percent since the birth of the solar system, an early Mars - one with noticeably less insolation - could have been an appreciably colder planet than today's, thus supporting this idea.
From the other, I suppose an early Mars' thicker atmosphere and more tectonic activity works in favour of warming the place up.
Quite which chair wins is not something I feel at all qualified to comment on.
Andy
Actually are there not 3 variables (armchairs) to consider?
1. Output from the sun (insolation at the upper atmosphere) increasing with time,
2. Atmospheric make-up and heat from impact/volcanic activity (decreasing with time), and
3. Distance from the sun (given the apparent instability of the early solar system as evidenced by the LHB, possibly increasing early on).
Ok - just a blip at the edge of the probability distribution but isn't a warmer wetter Mars a possibility worth consideration?
Not happy not knowing with which of the chairs to pick, I felt the need for a quick play with Excel.
Mars' average temperature today is around 210K. All things being equal, a 70%-as-bright Sun only knocks about 18K off that - a figure which I find a little suprising in terms of how relatively undramatic a change that is.
I can dial in a current-Earth-like atmosphere for this early Mars, and almost regain that 18K. Still cold and dry!
But consider a short-lived, even thicker atmosphere, one loaded with CO2 and water vapour pumped out by those gigantic volcanoes, and then the temperature starts to rise markedly. Is this the way to a warm, wet Mars? Sadly I don't think so, since this atmosphere comes at a price: it's going to seriously raise the albedo, dropping the temperature.
It's hard work to reach an Earth-like 288K.
Indeed, only towards the limits of Venusianess does the planet become balmy, which I think is extremely unlikely to have occured or extremely short-lived if it ever did.
So - for most of Mars' history - it's definitely the cold, dry chair for me.
Andy
If Mars ever had an Earth-density atmosphere, though, it would have had far more CO2 and thus a stronger greenhouse effect. Earth's atmosphere is unstable, maintained that way by life. Before plants, Earth had much more CO2 and less O2.
Are you taking into account the salinity of the sea, and also more methane than is currently observed?
The hypersaline lakes in the McMurdo Dry valleys remain ice free most of the year, and without tectonics the martian ocean could have been shallower than on Earth.
Which raises an interesting question. Could ice-covered lakes (like Lake Vostok, for example) still be present on Mars? How would one search for them? The ice would likely be mantled with dust and lag deposits. They would most likely occur at mid latitudes where ice is more stable. And they would likely be Amazonian in age (?). It seems if the zone of liquid water were shallow enough that MARSIS or SHARAD could detect the ice-water boundary. All questions I don't know the answer to. Does anyone know if anyone has looked into this?
Tom
http://mars.jpl.nasa.gov/express/mission/sc_science_marsis02.html
The evidence for a substantial ocean keeps on trickling in.
http://www.caltech.edu/content/evidence-martian-ocean
And at this particular time in Martian history, how was reality on the planet we live on?
There's some evidence (D/H ratio, I think) that Venus once had oceans as well, BTW.
But, machts nicht. If Mars OR Venus indeed did have oceans there's just no way to positively tell if they coexisted with those of the Earth, really. Terrestrial geological evidence from that era is at best fragmentary; the LHB was beating the hell out of the entire inner Solar System for a lot of that time.
The evidence is fragmentary yes, but compelling for continental crusts and oceans at 4.4 Mya ago (detrial zircons - Yilgarn Craton, Western Australia). At that stage Earth was just a baby and the LHB was just getting into stride. There is no certainty as to the LHB time scale or the impact intensity distribution over the period, but given the evidence from the moon and Mars for hefty impactors a cycle of ocean vaporisation and condensation, for both Earth and Mars seems more likely than not.
Strange to think that at one point Venus, Earth, and Mars, may have all had oceans at the same time. Three planets who may have started similarly, but have diverged dramatically since then. Also, given how new the surface of Venus is (i.e. 100 million years old?), perhaps its ocean lasted until relatively recently (in geologic terms). Maybe less then a billion years ago the oceans evaporated, than the plate tectonics stopped, and than the surface got covered in magma?
Regarding Venus, it's better to assume that we are *not* living in a special time in its history. The simplest explanation for its youthful surface age is of a stagnant lid with periodic overturn -- every several hundred million years the cold lithosphere (which is denser than the hot stuff below it) founders and sinks into the mantle, producing a global paroxysm of volcanic activity that wanes and then quiets for a long time until it all happens again. This isn't the only possible explanation, of course, but you have to make a very strong case for an ad-hoc explanation before you can convince people that the uniformitarian explanation is false. This is an odd duck though, a uniform process of repeated catastrophes. I wonder what Hutton would think
Well Curiosity seems to have confirmed that there was significant water during the Hesperian lasting millions to tens of millions of years. This is clear empirical evidence of a warmer, wetter Mars with neutral pH water.
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