Unit 1 Notes
Earth Structure, Materials, Systems, and Cycles Objectives
Since this course is about how Earth processes can adversely affect us as human beings, we need to first discuss some of the basic principles of the science of Earth - that is geology.
1. Earth's place in the Solar System and how it formed.
2. the structure of Earth and the materials from which it is made.
3. minerals and rocks, including the most important minerals and rocks for understanding natural disasters.
4. Earth processes, the energy that drives the processes, and the fundamentals of energy transfer in the Earth.
5. the time scale upon which Earth processes act.
6. plate tectonics - important in understanding earthquakes and volcanic eruptions.
7. geologic processes that cycle energy and materials through Earth systems.
The Earth in the Solar System
The Solar System
• The Earth is one of _____________ planets (eight if Pluto is not considered a planet) in the solar system
• In addition to the planets, many smaller bodies called asteroids, comets, meteoroids are present.
• All objects in the solar system orbit around the____________.
• The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) have ___________ densities because they are mostly composed of rock, and are called the Terrestrial Planets.
• The five planets outside the orbit of Mars (Jupiter, Saturn, Uranus, Neptune, and Pluto) have __________ densities because they mostly composed of gases, and are called the Jovian Planets.
The Planet Earth
Interior Structure of Earth
• The Earth has a radius of about _____ , although it is about 22 km larger at equator than at poles.
• Density, (mass/volume), Temperature, and Pressure increase with depth in the Earth.
• The Earth has a layered structure. This layering can be viewed in two different ways:
Compositional Layering
Crust
-
Continental
Ocean
-
Mantle
-
Core
Layers of Differing Physical Properties
-Lithosphere -
- Asthenosphere -
- Mesosphere -
- Outer Core -
- Inner core -
Minerals
The Earth is composed of rocks. Rocks are aggregates of minerals. Minerals are composed of atoms. In order to understand rocks, we must first have an understanding of minerals. We'll start with the definition of a Mineral.
A Mineral is
• Naturally formed
• Solid (it cannot be a liquid or a gas)
• With a definite chemical composition (every time we see the same mineral it has the same chemical composition that can be expressed by a chemical formula).
• and a characteristic ______________structure (atoms are arranged within the mineral in a specific ordered manner).
Examples
• Halite (salt) - Is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula NaCl, and does have a definite crystalline structure, as shown below. Thus halite is a mineral.
Important Minerals in the Earth's Crust
The variety of minerals we see depend on the chemical elements available to form them. In the Earth's crust the most abundant elements are as follows:
1. O, Oxygen 45.2% by weight
2. Si, Silicon 27.2%
3. Al, Aluminum 8.0%
4. Fe, Iron 5.8%
5. Ca, Calcium 5.1%
6. Mg, Magnesium 2.8% 7. Na, Sodium 2.3%
8. K, Potassium 1.7%
9. Ti ,Titanium 0.9%
10. H, Hydrogen 0.14%
11. Mn, Manganese 0.1%
12. P, Phosphorous 0.1%
Note that Carbon (one of the most abundant elements in life) is not among the top
Formation of Minerals
Minerals are formed in nature by a variety of processes.
Among them are:
• Crystallization from melt - the process that results in igneous rocks.
• Precipitation of water - the process that results in chemical sedimentary rocks.
• Precipitation from living organisms - the process that results in biochemical sedimentary rocks
• Change to more stable state - the process that results in the formation of soil, through weathering, and the formation of metamorphic rocks.
• Precipitation from vapor. (not common, but sometimes does occur around volcanic vents)
Since each process leads to different minerals, we can identify the process by which minerals form in nature. Each process has specific temperature and pressure conditions that can be determined from laboratory experiments.
Important Minerals for This Course
For the purposes of this course, three minerals that are most important (others may be introduced as needed) are:
Quartz - Chemical Formula SiO2. - Quartz is one of the primary minerals that originally forms by crystallization from a melt in igneous rocks. Although quartz is formed at relatively high temperatures it is stable (does not break down or alter) at conditions present near the Earth's surface. Thus quartz is a primary constituent of sand, soil, and sedimentary rocks called sandstones.
Clay Minerals - Clay minerals are sheet silicates, thus they have a crystalline structure that allows them to break easily along parallel sheets. Clay minerals form by alteration of other minerals during the process of chemical weathering (alteration under conditions present near the Earth's surface).
Calcite - chemical formula CaCO3 (calcium carbonate). Calcite is easily dissolved in water under slightly acidic conditions. Thus calcite can be precipitated directly from water. Organisms can extract the Calcium and Carbonate ions from water to precipitate their shells. Thus calcite is a primary constituent of chemical and biochemical sedimentary rocks.
Rocks
Rocks are aggregates of minerals that are held together to form a consolidated mass. The three general types of rocks are:
Igneous Rocks – If the crystallization takes place deep beneath the surface of the Earth they are called ____________. Examples include:
Granite -
Gabbro -
If the crystallization takes place on the surface of the Earth they are called __________________.
Examples include:
Rhyolite - a fine grained to glassy rock containing crystals of quartz, feldspar, and biotite - chemically the same as a granite.
Andesite - a fined grained rock containing crystals of pyroxene, plagioclase, and sometimes hornblende.
Basalt - a fine grained rock containing crystals of olivine, pyroxene, and plagioclase - chemically the same as a gabbro.
Sedimentary Rocks - rocks that form near the surface of the Earth through chemical precipitation from water or by cementation of loose fragments (called sediment).
Clastic Sedimentary Rocks - result from the cementation of loose fragments of pre-existing rock. The cementation occurs as a result of new minerals precipitating in the space between grains. Clastic sedimentary rocks are classified on the basis of the size of the fragments that makes up the rock
Name of Particle Size Range Loose Sediment Consolidated Rock
Boulder >256 mm Gravel Conglomerate (if clasts are rounded)
or Breccia (if clasts are angular)
Cobble 64 - 256 mm Gravel
Pebble 2 - 64 mm Gravel
Sand 1/16 - 2mm Sand Sandstone
Silt 1/256 - 1/16 mm Silt Siltstone
Cla.
