Contents:
Assignment 1
Question 1 Theory of Formation of Solar System Page 2
Question 2 Plate Tectonics 2
Question 3 The Earth's Structure
Question 4 The Law of Superposition 3
Assignment 2
Question 1 4
Question 2 Diagnostic Properties of Minerals 4
Question 3 Mineral Descriptions 4
Question 4 Igneous Rocks 5
Question 5 Distinguishing Rock Types 5
Question 6 Rock Forming Processes 6
Assignment 1
Question 1
Theory of formation of the solar system.
A star cluster forms in the spiral arm of the galaxy.
Very massive stars evolve rapidly and explode as supernovae on time scales of 10 and 10 years.
Shock waves from supernova collide with the cloud of gas and dust in interstellar space.
Supernovae debris including isotopes is mixed into the cloud.
The cloud is fragmented and collapses into a disc as a result of the shock wave.
A rotating disc of dust and gas forms the primitive solar nebula.
The Sun, and the giant gas-rich planets Jupiter and Saturn, begin to form in the gaseous nebula.
Strong solar winds from the early Sun sweep gas out of the inner Solar System, leaving a swarm of small planetesimals. This stage occurs within 10 years.
The inner planets form from planetesimals on a time scale of 10 years. The remaining gas is swept from the system or accumulates on giant planets.
Question 2 Plate Tectonics
(a) Continental drift describes how the crust of the earth is divided into mobile plates, moving around on the mantle. Sea floor spreading occurs where the tectonic plates are moving away from each other under the oceans. New rock material oozes out and solidifies to form submarine basalts, and pillow lavas.
(b) There are at least three items of evidence for continental drift.
1. Geological evidence. In some places rock types can be matched from one plate to an adjacent plate. For example, there are Mesozoic dolerites across the bottom of Africa that match rocks in Antarctica, and rocks matching from the eastern edge of South America to the western edge of Africa.
2. Biological evidence. Distributions of flora and fauna such as Glossopteris, and marsupial opossums have been cited as evidence for a connecting of continents.
3. Climatic evidence. The distribution of Carboniferous and Permian glacial deposits being interbedded with marine deposits around the world is used as evidence that once all of the continents must have been clustered about the pole.
c. Continental drift , sea floor spreading, and theory of plate tectonics.
(d) Plate boundaries are very dynamic places for rocks to be, a veritable Hollywood for rocks. Compared to plate boundaries, the rest of the earth's crust is relatively stable. Some of these rock forming processes are:
Earthquakes
Kinds of earthquakes
2. Volcanism
Hot spots are leftover volcanic traces when the plate has moved one. These hot spots can continue to contribute magmatic material to the continental plate as it moves along. Most of the igneous rocks have been formed at plate boundaries.
Kinds of Volcanoes:
3. Deformation
Most of the metamorphic rocks known today were created by deformation in a plate boundaries. The Himalayas were created by this method.
Kinds of deformation
Question 4
The Law of Superposition stated by Steno is that in an undisturbed sedimentary sequence the uppermost strata are younger than those on which they rest. This principle is used to determine the age of one layer of rock Relative to another, that is whether it is older or younger. Stratigraphic and palaeontologic methods enable us to construct a relative time scale.
Absolute ages of rocks are usually determined by radiometric dating. Absolute age represents the oldest possible age, that of formation. This is where the ratios of radioactive isotopes in a sample are compared. This is called isotopic dating. Knowing the decay constant and half-life it is possible to determine the age of a rock or mineral by accurately measuring the concentration of parent and daughter atoms of each isotope and comparing them. The ages which are determined can represent a variety of possible events and careful consideration must be given to their interpretation.
Assignment 2
Question 1
A rock is an assemblage of minerals. Sometimes a rock is one mineral. A mineral is a naturally occurring chemical compound which has a fixed chemical composition. Some minerals are chemical elements, for example, carbon and gold.
Question 2 Determination of Diagnostic Properties of Minerals.
(a) Colour
The sample is viewed under a bright light, and its colour determined.
(b) Hardness
The sample is scratched against some other mineral of a known hardness.
(c) Streak
The sample is rubbed across a ceramic streak plate, and the colour determined.
(d) Lustre
The sample is viewed under strong light, and the appearance of the reflected light is described.
(e) Crystal Habit
The shape of sample's crystals is described.
(f) Transparency
Describes how much light passes through the crystal.
(g) Specific Gravity
The sample is weighed. The sample goes for a bath, and weighed in the bath, by hanging on a string. The two masses are compared by
SG=
Question 3 Two sample minerals.
Olivine was found to have a light green colour, a colourless streak vitreous lustre, granular crystal habit, to be transparent and to have a hardness of 6.5. The mass of crystals was very fragile, and pieces kept falling out during the test.
Garnet was found to have a dark maroon almost black colour, a colourless streak, a vitreous lustre, a crystalline crystal habit, NO transparency and a hardness of 7. These rounded crystals make excellent paperweights, due to their high specific gravity.
Question 4
Distinguishing igneous from other rocks:
All of these characteristics are used in combination to determine whether a rock is igneous.
Texture:
Igneous rocks have unique textures due to the way that crystals form in a magma chamber (plutonic rocks) or from a volcano (volcanic). The crystals are not subject to any of the stresses during growth, as they are in a metamorphic rock.
Mineralogy:
Igneous rocks have unique combinations of minerals. Usually a high quantity of quartz and feldspar will indicate a felsic igneous rock.
Habitat: The surrounding rocks can help to indicate whether a particular rock is igneous, that is, the presence of other igneous rocks nearby or a chilled margin, or a metamorphic zone.
Question 5
(a) basalt and a schist
A basalt has a unique texture, of fine grained dark matrix, with larger acicular feldspar crystals. The schist would be foliated and contain mica, and the basalt would contain neither.
(b) Granite and a gneiss
A gneiss will have metamorphic foliation and texture that a granite will not.
(c) slate and a shale (mudstone)
As a slate has evolved from a shale, these rocks will have a similar fine grain size. Only the slate will have metamorphic foliation and cleavage. Possibly the slate will show visible mica, and shale won't.
(d) conglomerate and a coarse sandstone
A conglomerate has pebbles and cobbles in its formation, greater than 2mm. A coarse sandstone has a fraction that is 1-2mm.
Question 6 Describing Processes of Formation
All of these rocks have Deposition in their formation, where some other material, dirt, organic matter, bits of other rocks, trees or cars was transported by water or air and laid to be Lithified: hardened, into rock by burial and compaction.
(a) Conglomerate
Deposition Lithification
(b) Limestone
Deposition
The deposition material of a limestone is going to contain shells and leftovers of creatures, as well as bits of rock and dirt. Lithification
(c) Well-sorted sandstone
Deposition Lithification
During the deposition, the transport water slowed down or decreased over a long period of time to allow the sediments to become sorted.
(d) Schist
Deposition Lithification
Metamorphism is a process where rock is buried and reheated under great pressure, and the minerals recrystallise and reform into different rock.
(e) Marble
Deposition Lithification Metamorphism
Bibliography
Perspectives of the Earth, I.F. Clark and B.J. Cook, Australian Academy of Science, Canberra, 1983
Lecture Notes for Natural Resource Management: Geology 1998
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