6. Discussion (r.P – 8.1.5)

We’ll discuss the subject: «Plate tectonics in action». Pay attention to the words and expressions and pronunciation of some of the geographical names. Read the text, which will give you some necessary information. Use the earlier communicative formulas (Unit 7). Pay special attention to the questions, which will help you to underline what facts are more important.

Use the diagrams – «Plate tectonics in action», «Tectonic plates». (R.P. 8.2.10, 8.2.11)

Geographical Names

Eurasian Plate	Indo-Australian Plate	Nazca Plate
African Plate	Pacific Plate	South American Plate
Antarctic Plate	North American Plate

restless	непрекращающийся, неугомонный
jigsaw puzzle	картинка-головоломка, мозаика
abutting	примыкающий, прилегающий
diverging	расходящийся
colliding	сталкивающийся
slab	кусок, плита, блок
tectonic plate	тектоническая плита
coupled to	связанный / соединенный с
rigid	устойчивый, твердый
to ride upon	передвигаться / скользить по (поверхности)
convection current	конвективный поток
to shift	перемещать, сдвигать
margin -constructive -destructive -conservative -passive -active	граница -конструктивная -деструктивная -консервативная -пассивная -активная
lithosphere	литосфера
zone -collision -subduction	зона -столкновения -субдукции
spreading ridge	спрединговый хребет
to dive down	погружаться, нырять
to slide past	скользить мимо
to spark off	вызывать, порождать
boundary	граница, поверхность раздела
permutation	изменение
interlock	смыкаться

Earth’s changing surface

Our planet’s solid surface is a restless jigsaw of abutting, diverging and colliding slabs called plates (lithospheric plates). How plates behave forms the subject known as plate tectonics.

Each plate involves a slab of oceanic crust, continental crust, or both, coupled to a slab of rigid upper mantle. Collectively these plates make up the lithosphere. This rides upon the asthenosphere, a dense, plastic layer of the mantle. Heat rising through this layer from the Earth’s core and lower mantle seemingly produces convection currents that shift the plates above.

Plate activities produce three main kinds of plate margins.

• Constructive (divergent) margins are oceanic spreading ridges where new lithosphere is formed between two separating oceanic plates.

• Destructive (convergent) margins are oceanic trenches where an oceanic plate dives down below a (less dense) continental plate.

• Conservative (transform) margins are where two plates slide past each other and lithosphere is neither made nor lost.