by neufer » Thu Aug 05, 2021 3:54 pm
Chris Peterson wrote: ↑Thu Aug 05, 2021 2:37 pm
De58te wrote: ↑Thu Aug 05, 2021 10:55 am
The Moon may not have weathering today, but it was a different story 4 billion years ago. The Moon was half the distance from the Earth then. Today the Moon's tidal forces can raise oceans a few feet. Imagine the Earth's tidal force on the Moon when it was much closer. Moonquakes galore could have created rock slides. Moon volcanoes erupted. There are thousands of crater impacts. Each one blew gravel and dust up over the surface. Moon dust is not smooth as on Earth but has little jagged edges. When the dust fell back, it took a small chunk out of the crater wall, but only once, until the next impact. And it is believed that the Moon 4 billion years ago did have an atmosphere similar to Mars. That caused wind erosion. There is also temperature difference of 100s degrees between the shadows in the craters and the sunny side. Heat expansion could cause loose particle slides. The ancient atmosphere could be responsible for eroding the old large craters like Clavius, but the atmosphere was already gone when younger Tycho hit.
The Moon continues to experience weathering, in the form of a continuous bombardment of radiation, charged particles, dust, gravel, and occasional larger bodies, and moonquakes (as well as the thermal weathering you refer to).
- Dust, gravel, and occasional larger bodies
Whatever happened to micrometeoroids, meteoroids, and occasional meteors?
https://en.wikipedia.org/wiki/Tektite wrote:
<<Tektites (from Greek τηκτός tēktós, "molten") are gravel-sized bodies composed of black, green, brown, or gray natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of
Eduard Suess. They generally range in size from millimeters to centimeters. Millimeter-scale tektites are known as microtektites. Tektites are characterized by:
- a fairly homogeneous composition
an extremely low content of water and other volatiles
an abundance of lechatelierite
a general lack of microscopic crystals known as microlites and chemical relation to the local bedrock or local sediments
their distribution within geographically extensive strewn fields
Though the meteorite impact theory of tektite formation is widely accepted, there has been considerable controversy about their origin in the past. As early as 1897, the Dutch geologist Rogier Diederik Marius Verbeek (1845–1926) suggested an extraterrestrial origin for tektites: he proposed that they fell to Earth from the Moon. Verbeek's proposal of an extraterrestrial origin for tektites was soon seconded by the German geologist Franz E. Suess. Subsequently, it was argued that tektites consist of material that was ejected from the Moon by major hydrogen-driven lunar volcanic eruptions and then drifted through space to later fall to Earth as tektites.
The major proponents of the lunar origin of tektites include NASA scientist John A. O'Keefe, NASA aerodynamicist Dean R. Chapman, meteorite and tektite collector Darryl Futrell, and long-time tektite researcher Hal Povenmire. From the 1950s to the 1990s, O'Keefe argued for the lunar origin of tektites based upon their chemical, i.e. rare-earth, isotopic, and bulk, composition and physical properties.
Chapman used complex orbital computer models and extensive wind tunnel tests to argue that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater Tycho on the Moon's near side. O'Keefe, Povenmire, and Futrell claimed on the basis of behavior of glass melts that the homogenization, which is called "fining", of silica melts that characterize tektites could not be explained by the terrestrial-impact theory. They also argued that the terrestrial-impact theory could not explain the vesicles and extremely low water and other volatile content of tektites. Futrell also reported the presence of microscopic internal features within tektites, which argued for a volcanic origin.
At one time, theories advocating the lunar origin of tektites enjoyed considerable support as part of a spirited controversy about the origin of tektites that occurred during the 1960s. Starting with the publication of research concerning lunar samples returned from the Moon, the consensus of Earth and planetary scientists shifted in favor of theories advocating a terrestrial impact versus lunar volcanic origin. For example, one problem with the lunar origin theory is that the arguments for it that are based upon the behavior of glass melts use data from pressures and temperatures that are vastly uncharacteristic of and unrelated to the extreme conditions of hypervelocity impacts. In addition, various studies have shown that hypervelocity impacts are likely quite capable of producing low volatile melts with extremely low water content.
The consensus of Earth and planetary scientists regards the chemical, i.e. rare-earth, isotopic, and bulk composition evidence as decisively demonstrating that tektites are derived from terrestrial crustal rock, i.e. sedimentary rocks, that are unlike any known lunar crust.>>
[quote="Chris Peterson" post_id=315601 time=1628174236 user_id=117706]
[quote=De58te post_id=315594 time=1628160954 user_id=141631]
The Moon may not have weathering today, but it was a different story 4 billion years ago. The Moon was half the distance from the Earth then. Today the Moon's tidal forces can raise oceans a few feet. Imagine the Earth's tidal force on the Moon when it was much closer. Moonquakes galore could have created rock slides. Moon volcanoes erupted. There are thousands of crater impacts. Each one blew gravel and dust up over the surface. Moon dust is not smooth as on Earth but has little jagged edges. When the dust fell back, it took a small chunk out of the crater wall, but only once, until the next impact. And it is believed that the Moon 4 billion years ago did have an atmosphere similar to Mars. That caused wind erosion. There is also temperature difference of 100s degrees between the shadows in the craters and the sunny side. Heat expansion could cause loose particle slides. The ancient atmosphere could be responsible for eroding the old large craters like Clavius, but the atmosphere was already gone when younger Tycho hit.[/quote]
The Moon continues to experience weathering, in the form of a continuous bombardment of radiation, charged particles, dust, gravel, and occasional larger bodies, and moonquakes (as well as the thermal weathering you refer to).[/quote]
[list][b][i][color=#0000FF]Dust, gravel, and occasional larger bodies[/color][/i][/b] :?:
Whatever happened to micrometeoroids, meteoroids, and occasional meteors?[/list]
[quote=https://en.wikipedia.org/wiki/Tektite]
<<Tektites (from Greek τηκτός tēktós, "molten") are gravel-sized bodies composed of black, green, brown, or gray natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of [url=https://en.wikipedia.org/wiki/Eduard_Suess#Franz_Eduard_Suess]Eduard Suess[/url]. They generally range in size from millimeters to centimeters. Millimeter-scale tektites are known as microtektites. Tektites are characterized by:
[list] a fairly homogeneous composition
an extremely low content of water and other volatiles
an abundance of [url=https://en.wikipedia.org/wiki/Lechatelierite]lechatelierite[/url]
a general lack of microscopic crystals known as microlites and chemical relation to the local bedrock or local sediments
their distribution within geographically extensive strewn fields[/list]
Though the meteorite impact theory of tektite formation is widely accepted, there has been considerable controversy about their origin in the past. As early as 1897, the Dutch geologist Rogier Diederik Marius Verbeek (1845–1926) suggested an extraterrestrial origin for tektites: he proposed that they fell to Earth from the Moon. Verbeek's proposal of an extraterrestrial origin for tektites was soon seconded by the German geologist Franz E. Suess. Subsequently, it was argued that tektites consist of material that was ejected from the Moon by major hydrogen-driven lunar volcanic eruptions and then drifted through space to later fall to Earth as tektites.
[float=right][img3=Aerodynamically shaped australite caused by ablation of molten glass]https://upload.wikimedia.org/wikipedia/commons/3/3b/Australite_back_obl.jpg[/img3][/float]
The major proponents of the lunar origin of tektites include NASA scientist John A. O'Keefe, NASA aerodynamicist Dean R. Chapman, meteorite and tektite collector Darryl Futrell, and long-time tektite researcher Hal Povenmire. From the 1950s to the 1990s, O'Keefe argued for the lunar origin of tektites based upon their chemical, i.e. rare-earth, isotopic, and bulk, composition and physical properties. [b][color=#0000FF]Chapman used complex orbital computer models and extensive wind tunnel tests to argue that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater Tycho on the Moon's near side.[/color][/b] O'Keefe, Povenmire, and Futrell claimed on the basis of behavior of glass melts that the homogenization, which is called "fining", of silica melts that characterize tektites could not be explained by the terrestrial-impact theory. They also argued that the terrestrial-impact theory could not explain the vesicles and extremely low water and other volatile content of tektites. Futrell also reported the presence of microscopic internal features within tektites, which argued for a volcanic origin.
At one time, theories advocating the lunar origin of tektites enjoyed considerable support as part of a spirited controversy about the origin of tektites that occurred during the 1960s. Starting with the publication of research concerning lunar samples returned from the Moon, the consensus of Earth and planetary scientists shifted in favor of theories advocating a terrestrial impact versus lunar volcanic origin. For example, one problem with the lunar origin theory is that the arguments for it that are based upon the behavior of glass melts use data from pressures and temperatures that are vastly uncharacteristic of and unrelated to the extreme conditions of hypervelocity impacts. In addition, various studies have shown that hypervelocity impacts are likely quite capable of producing low volatile melts with extremely low water content. [b][u][color=#0000FF]The consensus of Earth and planetary scientists regards the chemical, i.e. rare-earth, isotopic, and bulk composition evidence as decisively demonstrating that tektites are derived from terrestrial crustal rock, i.e. sedimentary rocks, that are unlike any known lunar crust.[/color][/u][/b]>>[/quote]