Geology is the study of the Earth and its history

* Geologic Processes effect every human on the Earth all of the time, but are most noticeable when they cause loss of life or property. Such life or property threatening processes are called natural disasters. Among them are:
o Earthquakes
o Eruptions of Volcanoes
o Tsunamis
o Landslides
o Subsidence
o Floods
o Droughts
o Hurricanes
o Tornadoes
o Meteorite Impacts

# All of these processes have existed throughout Earth history, but the processes have become hazardous only because they negatively affect us as human beings. Important Point - There would be no natural disasters if it were not for humans. Without humans these are only natural events.

# Risk is characteristic of the relationship between humans and geologic processes. We all take risks everyday. The risk from natural disasters, while it cannot be eliminated, can, in some cases be understood in a such a way that we can minimize the hazard to humans, and thus minimize the risk. To do this, we need to understand something about the processes that operate, and understand the energy required for the process. Then, we can develop an action to take to minimize the risk. Such minimization of risk is called hazard mitigation.

Although humans can sometimes influence natural disasters (for example when road construction sets off a landslide), other disasters that are directly generated by humans, such as oil and toxic material spills, pollution, massive automobile or train wrecks, airplane crashes, and human induced explosions, are considered technological disasters, and will not be considered in this course.

# Some of the questions we hope to answer for each possible natural disaster are:

* Where is each type of disaster likely to occur and why?
* How often do these disasters occur?
* How can each type of disaster be predicted and/or mitigated?


The Earth in the Solar System

The Solar System

* The Earth is one of nine planets 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 Sun.

* The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) have high 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 low densities because they mostly composed of gases, and are called the Jovian Planets.

Origin of the Solar System
o Original Solar Nebula
o Condensation of the Sun about 6 billion years ago
o Condensation of the Planets about 4.5 billion years ago.
o Process is continuing today, although at a much slower rate.

The Planet Earth

Comparisons Between Earth and the Other Planets
o Earth similar in size density and structure to the terrestrial planets (all have metallic core, high density, composed of rock, with thin to non-existent atmosphere.

o Earth is the only planet with an atmosphere composed of Nitrogen, Oxygen, Carbon Dioxide, and Water Vapor.

o Earth is the only planet that has a hydrosphere, a region on the surface where water can exist in liquid, vapor and solid forms. This is due to the Temperature on the Earth's surface that usually remains between the freezing point of water, 0oC, and the boiling point of water, 100oC. Temperature on the Earth is controlled by the distance from the Sun and by the atmosphere of the Earth, which tends to moderate temperature variation.

o Earth is the only planet with a biosphere, (life sphere) which is made up of all living matter. The biosphere exists because of the Earth's temperature, and because of the atmosphere. Oxygen is present in the atmosphere because of the biosphere.
o Earth is the only planet with a regolith. Regolith is a thin covering of loose rock debris that has formed as a result of a process called weathering. Weathering is the mechanical and chemical response of interactions between the rocks of the Earth and its hydrosphere, atmosphere, and biosphere. While other planets have something resembling regolith, most formed as a result of meteorite impacts which have mechanically broken the surface into loose fragments of rock. The Earth is unique in that other processes have occurred to produce a more varied regolith.
Interior Structure of Earth
o The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at poles.

o Density, (mass/volume), Temperature, and Pressure increase with depth in the Earth.

o The Earth has a layered structure. This layering can be viewed in two different ways (1) Layers of different chemical composition and (2) Layers of differing physical properties.
* Compositional Layering
o Crust - variable thickness and composition
+ Continental 10 - 70 km thick
+ Oceanic 8 - 10 km thick
o Mantle - 3488 km thick, made up of a rock called peridotite.


+ Core - 2883 km radius, made up of Iron (Fe) and small amount of Nickel (Ni)