ESSAY QUESTIONS

Essay Questions

Essay Questions

Questions 1

Determining the age of materials by means of their radioactive content is called radiometric age dating or radiometric dating. Earlier dating of rocks, minerals and other Earth materials resorted to deductive methods. Rock strata were compared in different regions and only by growing knowledge of the physical processes involved in their forming, could Scientists estimate the time needed for the specific formative process to have taken place.

Near the end of the 19th century a more precise tool, for dating past Earth-events, were gained. Radiometric age-dating is based on the fact that every radioactive element decays. The original or "parent" element emits radiation and particles until the loss thereof transforms it into a stable "daughter" element. A series of transformations into other radio-active elements marks its unparalleled pattern and rate of decay until it reaches stability.

The Law of Radioactivity describes the decay of radioactive elements and their resulting formation. A simple mathematical formula incorporates the decay rate of the parent element and calculates the ratio of the daughter element to the parent element after a given period of time. The concentration of the chemical elements must be measured as well as their isotopic composition.

Assumptions and Weaknesses of Radiometric Dating

Most rock dating methods rely on the following basic assumptions:

Initial conditions are known

Initial ratio of daughter/parent isotopes is known (zero date problem)

A constant decay rate

There is no leaching or addition of parent or daughter isotopes

Questions 2

A volcano is an opening in the Earth's crust through which molten rock (magma), gas and ash erupt, often with powerful force. The word 'volcano' can be used to describe the opening itself or the cone-shaped mountain that is built up around it. Volcanic eruptions are caused by the growing pressure of gas that has built up in the magma. When the pressure becomes too great the magma is forced onto the Earth's surface, where it is known as lava.

Some magma cools and solidifies on its way upwards and may be blasted out as enormous chunks of hot rock, or as volcanic ash and dust. Currents of very hot gas and rock particles, called pyroclastic flows, may sweep over the landscape at high speed destroying everything in their path. Dust can remain in the atmosphere for years and cause vivid sunsets all over the world (Benton, 2005: 44).

The nature of a volcano depends on how viscous, or sticky, the magma is. This depends on its temperature and the amount of silica (a mineral) it contains.

If the silica content is low, the lava flows out gently, forming a shallow shield-shaped cone. Lava with a very high silica content erupts slowly to form a dome, usually within an existing crater. Composite volcanoes cause the most dangerous, highly explosive, eruptions. These are volcanoes with alternate layers of rock and lava. The magma is moderately viscous and it is mixed with other materials.

The Earth's surface is divided into several plates, known as tectonic plates, which are moving all the time. Most of the Earth's active volcanoes are located along ...