L6 - Lunar Geology Flashcards
What is a mineral?
A mineral is a solid material of well-defined composition, formed by natural processes. Its atoms are arranged in a regular pattern and because of this, minerals form crystals with characteristic shapes e.g. diamond (crystalline carbon).
What is a mineral?
A mineral is a solid material of well-defined composition, formed by natural processes. Its atoms are arranged in a regular pattern and because of this, minerals form crystals with characteristic shapes e.g. diamond (crystalline carbon).
What is a rock?
A rock is any naturally-formed solid assemblage of mineral grains:
• The mineral grains may be fragments of crystals or intact crystals
• A rock usually contains several mineral types (not just one)
• Rocks are classified according to the way their grains are arranged (although the identity of grains present and dominant size of mineral grains are also important)
The shape of the grains in a rock, their size and the relationship between them define the texture of a rock, and reflect the process that formed it.
Characteristics of Sedimentary Rocks?
Weathering, erosion, transport and deposition of sedimentary material result in a rock with a fragmental texture i.e. grains are cemented together with spaces between individual grains.
Characteristics of Igneous Rocks?
Formed by solidification of liquid magma (underground or at the surface). These rocks have an interlocking, intergrown, crystalline texture with randomly orientated crystals.
Characteristics of metamorphic Rocks?
Any rock type that has been heated to a few hundred degrees Celsius and/or been subjected to high pressure (because of weight of overlying rocks). Metamorphism occurs in solid state only. Minerals become chemically unstable i.e. their ions redistributed to form larger crystals or new minerals. They have an intergrown texture (like igneous rocks) but with many crystals aligned or arranged in parallel bands.
Explain how most lunar geological features (mountains, craters, maria, rilles, etc.) formed and contrast this to how most geological features formed on Earth.
No, most lunar features formed as a result of meteorite bombardment and volcanism. In contrast, the Earth is much more geologically active and, in addition to volcanism and early meteorite bombardment features, has been sculpted by:
• Plate-tectonic activity (mountain-building, subduction and sea-floor spreading)
• Strong atmospheric and oceanic effects e.g. abrasion by wind, frost, running water (rivers, coastal erosion), ocean tidal activity, etc.
Explain why lunar dust has been described as the “No. 1 environmental hazard on the Moon”.
• Scientific instruments destroyed by overheating
= Adsorbed dust absorbs more solar photons making devices overheat
• Opaque dust clouds making lunar capsule descent manoeuvres dangerous
=Dust clouds generated by lunar module descent thrusters
• Abrasion on moving parts
=Adsorbed dust is composed of hard and abrasive minerals, e.g. silicates and oxides
Explain what the discovery of abundant anorthosite rocks in the lunar highlands revealed to Geologists.
Anorthosite rocks abundant in lunar highlands. Anorthosites are plutonic igneous rocks i.e. a rock formed by slow crystallization composed almost entirely of one silicate mineral: plagioclase feldspar (alumino silicates with variable Na and Ca). Just one mineral is a rock suggests that it formed due to floating or sinking in magma (molten rock below surface). Hence, it is believed that the Moon was surrounded by a huge ocean of magma soon after it formed
Explain the Magma Ocean Concept. (EXAM!!!)
When Moon formed it was enveloped by a layer of molten rock (magma) hundreds of km thick. As magma crystallized, the denser minerals sank while the less dense ones (such a feldspar) floated. Hence, the Moon developed an ancient anorthosite crust. The dense minerals (olivine and pyroxene) later re-melted to produce the basalts that compose the maria.
Explain why it is unlikely that water ever flowed on the lunar surface.
No evidence has been found:
• All Earth rocks contain some evidence of water
• Apollo 15 collected regolith samples from Hadley Rille. A “rille” is a river-like channel where lava flowed during the eruption of mare basalts
• All samples collected showed no mineralogical/geochemical evidence to suggest that water formed these features
• The Moon (apart from possible polar ice) is “as dry as a bone”
Explain why some 26% of the near side of the Moon‟s surface unlike 2% for the far side.
Basalt is not evenly distributed on the lunar surface. Nearly 26% of the near side of the Moon is basalt and only 2% of the far side is basalt. Most basalt in either hemisphere is found in areas of lowest elevation, particularly in the very large impact basins.
Explain the Ejected Ring Theory of lunar formation and why it remains the most credible theory of how the Moon formed.
- A projectile as large as Mars collides with the “nearly-completed” Earth 4.5-4.6 Billion years ago.
- Metallic core of projectile gets added to Earth’s core (predicted by computer simulation).
- Much of rocky mantles of Earth and projectile vaporized.
- Some of this vaporized debris orbits Earth and, eventually, accretes to form the Moon.
Explain how Geologists can differentiate between lunar rocks and rock from Earth.
- Establishing the age of the rock e.g. Argon method. Moon rocks are usually >3 billion years (unlike terrestrial rocks).
- The fact that lunar rocks don’t have minerals associated with the presence of water e.g. amphiboles, an important group of rock-forming silicates, including hornblende [Ca2(Mg, Fe, Al)5 (Al, Si)8O22(OH)2], the commonest.
- The fact that lunar rocks are depleted in volatile elements e.g. Na, Z, Pb, Hg, etc.
- Looking for enrichment of certain elements e.g. the Moon’s KREEP rocks (potassium, Rare Earth elements, phosphorous).
What is a rock?
A rock is any naturally-formed solid assemblage of mineral grains:
• The mineral grains may be fragments of crystals or intact crystals
• A rock usually contains several mineral types (not just one)
• Rocks are classified according to the way their grains are arranged (although the identity of grains present and dominant size of mineral grains are also important)
The shape of the grains in a rock, their size and the relationship between them define the texture of a rock, and reflect the process that formed it.
