DBH 3.
BIOLOGY & GEOLOGY
Tectonic plates theory
The Tectonic Plates Theory was formulated in the 1960´s. According to this theory:
- The outermost solid part of the Earth, the litosphere, is divided into large blocks called tectonic plates that fit together in the same way as pieces of a giant jigsaw puzzle.
- The plates float on top of the asthenosphere, the layer just below the litosphere. The asthenosphere is denser than the litosphere and is partially formed by molten materials that circulate in convection currents.
- The convection currents of the asthenosphere are the engine that moves the tectonic plates.
ACTIVITIES
Search for new vocabulary and build up a particular section of related vocabulary.
1. Define these terms:.
a. Tectonic Plates.
b. Convection current.
c. Asthenosphere.
2. Complete the following chart.
The points where two tectonic plates meet are called boundaries. Earthquakes, volcanic eruptions, formation of mountain ranges and rocks deformation are most likely here.
The plates can move one with respect to another in different ways:
a) Divergent boundaries:
When plates separate they form a divergent boundary. Materials from the inside of the Earth rise up between the plates forming new litosphere and provoking their separation. The limit between the plates is a ridge. For example, in the middle of the Atlantic Ocean, the Atlantic ridge separates the African and the South American Plates.
b) Convergent boundaries
When plates collade they form a convergent bounday. These limits can be of two types:
- When one plate collades by its continental side with other by its oceanic side, the oceanic plates sinks undernearth the other one (subduction). The subducting plate is destroyed, molted into the asthenophere. When plates converge they cause earthquakes and form volcanic mountain ranges in the continent and trench in the ocean. For example, Nazca Plate is subducting undeerneath South American Plate, forming the Andes Mountain Range.
- When two plates collide by their continental sides neither one non another subduct. In this case, a huge mountain range is formed and plates fuse (obduction). For example, African Plate is colliding with the Eurasian Plate forming the Pirineos and the Alpes.
c) Transform boundaries
When plates slide past each other, moving in opposite directions, they form a transform boundary. The friction between the plates provokes intense earthquakes, but litosphere is neither created nor destroyed. This limit is called transform fault. An example of this is San Andres´s fault between the North American and Pacific Plates.
