GEOLOGY

GEOLOGY: What does it mean?

It is the science of the composition, structure, history of the Earth.

The geology of an area is the base that determines what life is able to occur in that area. And what are the interrelationships between rocks, soil, climate, vegetation and animals.

The GEOMORPHOLOGY refers to the way in which the geology influences the shape of the landscape.

The TOPOGRAPHY is the shape of the landscape that is influenced by the geology of the area.

The GEOLOGY influences Ecosystems:

• Rocks are broken down to form soils (sand, clay, mud...).
• Soil type, result of interaction of geology, climate, geomorphology.
• Type of vegetation, result of interaction between the soil and the climate.
• Animal species are there because vegetation is available and the climate suits them.

The WEATHERING is the disintegration and decomposition of rocks and minerals by natural processes (action of  frost or ground water...)

The EROSION is the gradual wearing away rock or soil by physical, biological or chemical breakdown, and the transportation of materials away by water, wind or ice.

THE COMPOSITION OF EARTH

It is made up of a very dense core, a dense mantle and a thin outer crust.

GRAVITY and HEAT are the 2 main factors that shape the Earth. The force of gravity causes heavy metals such as iron to be concentrated at the core, while the lighter materials like Mg or Al silicates are found near the crust. Heat creates large-scale convection currents in the mantle that cause large slabs of upper mantle and crust (called plates) to move around the surface of the Earth.

The CONVECTION circulatory movement is a liquid or gas, resulting from regions of different temperatures and different densities rising and falling in response of the force of gravity.

3 rock types exist: Igneous rocks (volcanic); Sedimentary rocks; Metamorphic rocks

IGNEOUS ROCK

They are formed when the hot magma rises up from the lower crust or the upper mantle and then cools down and becomes a solid mass (2 types: Extrusive and Intrusive)

Extrusive igneous rocks are formed when the magma is ejected from the crust onto the surface of Earth, cools down and becomes solid (Ryolite, Basalt).

Intrusive igneous rocks are formed when a molten rock mass (magma) cools down and solidifies beneath the surface of Earth (Granite, Gabbro, Dolerite).

MAGMA is a molten (liquid) rock before it erupts on the surface of the earth.

LAVA is a molten rock erupted from a volcano or a fissure on land or the ocean floor and solidified as rock on the surface of the earth.

Lava that cools down quickly forms igneous rocks with small crystals (fine grained).

Extrusive igneous rocks developed from magma that reaches surface as a lava-flow, cools down rapidly.

Intrusive igneous rocks cool down at a slow rate and form rocks with large crystals (coarse grained).

SEDIMENTARY ROCKS

They are made up of sediments that originated through physical or chemical processes or through the accumulation of organic remains. These sediments may then be buried, compacted and transformed into rocks. This process is called LITHIFICATION (process in which loose sediments [particles] are changed into solid rock).

There are 2 types of sedimentary rocks: of mechanical origin and of organic matter origin. 

• Mechanical origin: Most common rocks. Sedimentary rocks are composed of mineral particles produced by the mechanical disintegration (weathering and erosion) of other rocks. Fragments are transported by wind, rain, flowing water into larger bodies of water, where they are deposited in layers as sediments. These sediments accumulate. When they are buried they become compacted by the material abose. This material then becomes cemented by seeping waters to form a rock. ex: shale (sedimentary rock derived from clay or silt); sandstone (from sand).
• Organic matter origin: when organic matter from plants and animals accumulate. ex: Limestone: accumulation of skeletons (calcium carbonate) of marine animals (shells, corals...); and Coal: carbon containing sediments formed from organic matter (degraded wood, plant debris, spores, algae).

METAMORPHIC ROCK

Rock in which the original composition and texture of a solid rock have been altered through high temperature and/or pressure. Rocks go through metamorphic changes in mineralogy (re-crystallisation) and usually a change in texture of the rock. The metamorph involves a change in physical form, appearance or character.

ROCKS FORMING MINERALS

Rocks are usually made up of a mixture of minerals. Few rocks are entirely of 1 mineral (called Native element).

A MINERAL is a naturally occuring inorganic crystalline substance with a well-defined chemical composition and a constant geometrical arrangement of its atoms and ions.

An ATOM is the smallest portion into which an element can be divided and still retain its properties.

IRON is an atom or group of atoms that has acquired an ellectric charge by loosing or gaining 1 or more electrons.

Minerals properties:

• substance that cannot be broken down into other substance by chemical means.
• each mineral is know by its short chemical formule (ex: SiO2).
• Most minerals will form crystals if they are allowed to grow unrestricted.
• are formed through the process of CRYSTALLISATION.

PROPERTIES OF 2 COMMON ROCK TYPE:

ROCK and THEIR MINERALS: