by johnnydeep » Thu Sep 16, 2021 1:06 pm
JohnD wrote: ↑Thu Sep 16, 2021 9:26 am
Thank you, Chris, and Johnnydeep!
Although I still can't see how
"where now there is a mountain, there once was a lake..... the lake may have only been a few meters deep, just enough to form those sandstone deltas and thin layers of mud. But fluctuations in the water supply or the climate allowed this to happen over and over, slowly building up the mountain." Eh, what? Gale Crater was the result of an impact, billions of years ago. Yes, it may have contained a lake afterwards, but Mount Shapr is the central peak of the crater, formed by slumping. Any sediment would have formed much, much later, and the peak will not contain sediment, but pulverised crater contents.
Mountains of course may contain sedimentary rocks, but they are built up by tectonic action, after they have settled at the bottom of a body of water. Here, the lake formed
after Mount Sharp was formed, so I'm not satisfied by NASA's answer. I'm surprised that enquiring minds do so!
...
John
You made me look some more. Still not entirely clear to me either, particularly with respect to whether the peak of Mount Sharp was ever under water or not, but I'd think not. So, the most sense I can make of it is that sediment from flowing water only helped build the lower levels of Mount Sharp, and the peak should be sediment free...unless perhaps affected by rains over millions of years? From
https://en.wikipedia.org/wiki/Mount_Sharp
Formation
The mountain appears to be an enormous mound of eroded sedimentary layers sitting on the central peak of Gale. It rises 5.5 km (18,000 ft) above the northern crater floor and 4.5 km (15,000 ft) above the southern crater floor, higher than the southern crater rim. The sediments may have been laid down over an interval of 2 billion years,[20] and may have once completely filled the crater. Some of the lower sediment layers may have originally been deposited on a lake bed,[20] while observations of possibly cross-bedded strata in the upper mound suggest aeolian processes.[21] However, this issue is debated,[22][23] and the origin of the lower layers remains unclear.[21] If katabatic wind deposition played the predominant role in the emplacement of the sediments, as suggested by reported 3 degree radial slopes of the mound's layers, erosion would have come into play largely to place an upper limit on the mound's growth.[24][25]
On December 8, 2014, a panel of NASA scientists discussed (archive 62:03) the latest observations of Curiosity about how water may have helped shape the landscape of Mars, including Aeolis Mons, and had a climate long ago that could have produced long-lasting lakes at many Martian locations.[26][27][28]
On October 8, 2015, NASA confirmed that lakes and streams existed in Gale crater 3.3 - 3.8 billion years ago delivering sediments to build up the lower layers of Mount Sharp.[29][30]
On February 1, 2019, NASA scientists reported that Curiosity had determined, for the first time, the density of Mount Sharp in Gale crater, thereby establishing a clearer understanding of how the mountain was formed.[31][32]
And from
https://en.wikipedia.org/wiki/Gale_(crater)
Geology
An unusual feature of Gale is an enormous mound of "sedimentary debris"[21] around its central peak, officially named Aeolis Mons[5][6] (popularly known as "Mount Sharp"[22][23]) rising 5.5 km (18,000 ft) above the northern crater floor and 4.5 km (15,000 ft) above the southern crater floor—slightly taller than the southern rim of the crater itself. The mound is composed of layered material and may have been laid down over a period of around 2 billion years.[3] The origin of this mound is not known with certainty, but research suggests it is the eroded remnant of sedimentary layers that once filled the crater completely, possibly originally deposited on a lakebed.
So was the central peak of Gale crater originally a much smaller peak created by the impact, and later built up over a billion plus years by sedimentary deposition to be even higher, so that even the top of Mount Sharp was once entirely under water? I'm not sure. I don't think Curiosity will ever get to the peak... or will it?
[quote=JohnD post_id=316710 time=1631784394 user_id=100329]
Thank you, Chris, and Johnnydeep!
Although I still can't see how [i]"where now there is a mountain, there once was a lake..... the lake may have only been a few meters deep, just enough to form those sandstone deltas and thin layers of mud. But fluctuations in the water supply or the climate allowed this to happen over and over, slowly building up the mountain." [/i] Eh, what? Gale Crater was the result of an impact, billions of years ago. Yes, it may have contained a lake afterwards, but Mount Shapr is the central peak of the crater, formed by slumping. Any sediment would have formed much, much later, and the peak will not contain sediment, but pulverised crater contents.
Mountains of course may contain sedimentary rocks, but they are built up by tectonic action, after they have settled at the bottom of a body of water. Here, the lake formed [u]after[/u] Mount Sharp was formed, so I'm not satisfied by NASA's answer. I'm surprised that enquiring minds do so!
...
John
[/quote]
You made me look some more. Still not entirely clear to me either, particularly with respect to whether the peak of Mount Sharp was ever under water or not, but I'd think not. So, the most sense I can make of it is that sediment from flowing water only helped build the lower levels of Mount Sharp, and the peak should be sediment free...unless perhaps affected by rains over millions of years? From https://en.wikipedia.org/wiki/Mount_Sharp
[quote][b][size=150]Formation[/size][/b]
[b][color=#0000FF]The mountain appears to be an enormous mound of eroded sedimentary layers sitting on the central peak of Gale[/color][/b]. It rises 5.5 km (18,000 ft) above the northern crater floor and 4.5 km (15,000 ft) above the southern crater floor, higher than the southern crater rim. The sediments may have been laid down over an interval of 2 billion years,[20] and may have once completely filled the crater. Some of the lower sediment layers may have originally been deposited on a lake bed,[20] while observations of possibly cross-bedded strata in the upper mound suggest aeolian processes.[21] However, this issue is debated,[22][23] and the origin of the lower layers remains unclear.[21] If katabatic wind deposition played the predominant role in the emplacement of the sediments, as suggested by reported 3 degree radial slopes of the mound's layers, erosion would have come into play largely to place an upper limit on the mound's growth.[24][25]
On December 8, 2014, a panel of NASA scientists discussed (archive 62:03) the latest observations of Curiosity about how water may have helped shape the landscape of Mars, including Aeolis Mons, and had a climate long ago that could have produced long-lasting lakes at many Martian locations.[26][27][28]
[b][color=#0000FF]On October 8, 2015, NASA confirmed that lakes and streams existed in Gale crater 3.3 - 3.8 billion years ago delivering sediments to build up the lower layers of Mount Sharp.[29][30][/color][/b]
On February 1, 2019, NASA scientists reported that Curiosity had determined, for the first time, the density of Mount Sharp in Gale crater, thereby establishing a clearer understanding of how the mountain was formed.[31][32][/quote]
And from https://en.wikipedia.org/wiki/Gale_(crater)
[quote][b][size=150]Geology[/size][/b]
An unusual feature of Gale is an enormous mound of "sedimentary debris"[21] around its central peak, officially named Aeolis Mons[5][6] (popularly known as "Mount Sharp"[22][23]) rising 5.5 km (18,000 ft) above the northern crater floor and 4.5 km (15,000 ft) above the southern crater floor—slightly taller than the southern rim of the crater itself. [b][color=#0000FF]The mound is composed of layered material and may have been laid down over a period of around 2 billion years.[3] The origin of this mound is not known with certainty, but research suggests it is the eroded remnant of sedimentary layers that once filled the crater completely, possibly originally deposited on a lakebed.[/color][/b][/quote]
So was the central peak of Gale crater originally a much smaller peak created by the impact, and later built up over a billion plus years by sedimentary deposition to be even higher, so that even the top of Mount Sharp was once entirely under water? I'm not sure. I don't think Curiosity will ever get to the peak... or will it?