Tutor profile: Cole P.
Explain the role of alumino-silicate minerals in determining the protolith of a metamorphic rock. What do they form from, and can they occur in igneous rocks?
Metamorphosed terrigenous sediments that have been derived from the weathering and erosion of granites have aluminosilicate minerals like kyanite and sillimanite because these are metamorphic minerals that form due to the Al-bearing clay phases in the parent sediment. The incongruent weathering of feldspars in granites produces these Al-bearing clay phases, which then become present in the sedimentary protolith before metamorphism. When the sedimentary rock containing the clays is subjected to higher pressure and temperatures, the phases turn into the distinct metamorphic aluminosilicate minerals. Fresh igneous rocks do not contain these minerals because igneous rocks crystalize directly from a magma melt, and the aluminosilicates are not stable at such high magmatic temperatures.
Subject: Earth Science
This question involves a scenario of interdisciplinary planetary science field analysis. Use your Earth science skills, combined with elements of Earth geology, to solve the problems on another planet. It is the year 2047. You and your team arrive at a new field site on Mars that has never been analyzed or visited before. The group observes the following: The site is a large valley with tributary networks entering it. It give a great cross section view of the deposits on both sides. You notice there are regions of mass wasting, landslides, and evidence of extensive hydrologic activity. There are massive boulders that seem out of place sitting atop finer grained sediments and sandstones. Some regions seem as if they have undergone past volcanic activity, and seem to be related to the hydrologic evidence. Your team of 4 consists of a astrobiologist, a geochemist, and an geotechnical engineer. You are the group's leader and the planetary geologist. Use your best judgement to create a plan for how to efficiently analyze the site, and how would you go about analyzing the various deposits based on their extremely varying grain sizes? What elements are key for creating a map? This answer can have as much or as little creativity, just be sure to keep all principles of Earth science in mind.
The first thing to do is to delegate tasks based on the skills of the team. Next, start these tasks by breaking up into teams of two. re-congregate and re-evaluate tasks based on the initial findings. Work as a full team to decide what is the best course of action for finding future settlements and the safest locations. Make a map of the region as a team and organize the samples based on this location map. Ultimately, the goal would be to create a interactive DEM of the region, highlighting geologic, geographic, and hydrologic differences, sample locations, relative ages and rock types, potential for future colonization, and other interesting features (such as volcanic lava tubes or confusing elements that require more research). The astrobiologist and the engineer would start in the areas of mass wasting and hydrologic activity, because those are the regions where we would expect life to have existed in the rock walls, evidenced by the saturation of water that induced the mass wasting. The engineer would team with the astrobiologist to determine the best locations for drilling into the cliff sides boreholes in certain layers to search for evidence of past life. The astrobiologist would continue to sample the wetter regions and determine future areas for borehole drilling down at the base of the valley. The geochemist would team up with the leader, you, as the planetary geologist and start from the bottom of the sequences to start relative dating of the sediments and preliminary absolute dating techniques. After a general stratigraphy has been established, the group would team up together to figure out what the sedimentology was and start theorizing on potential environments, for example: tsunami deposits or glacial drop-stones to explain the large boulders sitting in the fine grained sediments. the planetary geologist would team up with the engineer do begin geomorphological calculations on the frequency and intensity of the landslides and mass wasting. The engineer would make calculations on the total energy required to produce the mass wasting events and landslides, by measuring the scarps and masses of alluvium with the laser-precision detectors. While this aspect of the analysis was being conducted, the geochemist and the astrobiologist would continue to search for the areas of volcanic activity for the potential of lava tubes, or volcanic rocks for future colonizes to shield them from radiation. These areas would be inspected for potential past life through a slew of geochemical tests and analyses. Get the group together and ultimately come to conclusions about the various tests that have been done on the first day and begin planning for future returns to the site.
Compare and contrast the formation and evolution of the TRAPPIST-1 exoplanetary system (7-planet resonant system around a small m-dwarf – search on Google for more information) to the formation and evolution of our solar system, and speculate as best you can on the causal relationships for these differences. Use 333,000 M⊕ for the mass of our sun and 26,000 M⊕ for the mass of TRAPPIST-1. Any other numbers or constants can be requested by the proctor, or found online, but are not necessary.
In planetary formation and dynamics, the fundamental characteristics that determine the end-result (planetary system) of a planetary accretion disc are primarily the temperature gradient and total mass of the disc. Of lesser importance are the rotational velocities of the disc, metallicity of the parent nebula, and other conditions within the stellar nursery, which could produce chaotic formation events, limiting the number of planets in a given system. For our purposes in this comparison, the temperature gradient depends on the temperature of the star (i.e. the mass of the star) and the total mass of the disc is dependent on the regional mass of the stellar nebulae that the disc condensed from. In the case of TRAPPIST-1, the star is an M-dwarf star. Comparing the mass of our own star (Ms) to the mass of this star (Mt), the ratio becomes: Ms/Mt = 333,000 M⊕ / 26,000 M⊕ = 12.8. This means that our star is 12.8 times more massive than TRAPPIST-1, and therefore we can assume the mass of the initial regional nebulae was around 1 order of magnitude smaller during formation of their system (10^-1). This would allow the planets that formed around TRAPPIST-1 to be much more centralized, and as we know, their orbits are consistent with this estimate, as they orbit well within the distance from our sun to Mercury. We expect the formation and initial evolution of this system to be therefore dominated by strong orbital resonances and not much planetary migration, which is consistent with the models of the TRAPPIST-1 system that show tidal locking and harmonic orbits that would prevent migration. In the formation of our solar system, the temperature gradient allowed the Jovian gas giant planets past the frost line to accumulate their gasses and then migrate further outward. It is possible that in the TRAPPIST-1 system that during formation of these planets, that their high temperature gradient (due to proximity to the host star) in the region of growing planetesimals was limited to rocky terrestrial worlds. This would have left the planets in a similar state (approx. current masses) when the stellar wind turned on and expelled the excess gas, preventing further accretion of the terrestrials into super-earth sized worlds and Jovian worlds. Their stable orbits since formation would have prevented migration, combined with the approximate condensation mass can both explain their observed orbit locations and relatively small sizes. The uniqueness of this system compared to our solar system can be seen in terms of the orbital geometries and stellar sizes. The question of habitability and water content of these world could be explained through further discussion of the formation and evolution of this system.
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