Earth and Life Science

OBJECTIVES

Compare the relative size and material properties of Earth's core, mantle and crust.

Relate the principal differences between oceanic and continental crust.

Contrast the lithosphere with the asthenosphere.

Differentiate between minerals and rocks.

Recall the definitions of the major categories of igneous, sedimentary, and metamorphic rocks.

Explain the meaning of the rock cycle.

90 million years ago, Earth has a big changes from now, like how life forms, including dinosaurs. We would see the big different spatial distribution of land and water. And also the shape and size of the oceans and continents are very different from what they are today. They said that forest grew above the present Arctic Circle, and grasses did not exist yet. How does it happen? According to this chapter all differences between then and now in the size, shape and distribution of mountains ranges and water bodies, and the accompanying differences in climate, soil and organism, are require scientific explanation.

EARTH'S PLANETARY STRUCTURE

The science of physical geography had been focus on Earth's surface. Now let's know the planet's internal structure,composition, properties and processes, it is needed to understand many aspects of Earth's natural surface characteristics. From low density gas molecules in the outermost layer of the atmosphere to high density iron and nickel at the center of the planet. Gas, Liquid and Solid matter are need to consist the Earth system by gravitational attraction. According to Sir Isaac Newton that the degree to which particles are drawn to each other by gravity depends on the mass of each particle, which is commonly expressed in units of grams or kilograms. So it is say that, the particles that are drawn to each other by gravity is depends on the mass of each particle. For those object that have a greater gravitational force of attractions it means that it has a larger mass. So if the object has a low gravitational force it means it has a low mass. Those types of earth materials that have the greatest density is also have the greatest gravitational attraction, and as a result they have tended to concentrate close together at and near the center of earth. Scientist are continually working to learn more about Earth's interior because most of what we know about Earths internal structure and composition has not been resolve but it puts to indirect conclusion by various forms remote sensing.

But because of the evidences of scientist that conclusion was change because scientist use that evidence to gain indirect knowledge of Earth's interior is the behavior of various shocks waves known as seismic waves, as they move through the planet. Scientist have an instrument to track seismic waves of earthquakes as they travel through earth and it is called seismograph this instrument can record seismic waves from an earthquake even when the earthquake is centered thousands of kilometers away from the seismograph's location . Earthquake can produce two major types of seismic waves that has different speeds. It is the P waves and S waves ; the P waves or primary waves are the one who can travel faster and the one who first to arrive at recording seismograph and the S waves or secondary is the one who travel more slowly than P waves.

CORE

Earth’s innermost section, the core, contains one third of Earth’s mass and has a radius of about 3360 kilometers (2100 mi), which is larger than the planet Mars. Earth’s core is under enormous pressure- several million times atmospheric pressure at sea level. Scientific have deduced that the core is composed primarily of iron and nickel and consist of two distinct sections, the inner core and outer core.

        Inner core has a radius of about 960 kilometers (600 mi). The speed of P waves travelling through the inner core shows that it is a solid with a very high material density of about 13 grams per cubic centimeter (o.5 lbs/in.). The outer core forms a 2400-kilometer (1500-mi) thick band around the inner core. Rock matter at the top of the outer core has a density of about 10 grams per cubic centimeter. Because the outer core blocks the passage of seismic S waves, earth’s scientists know that the outer core is molten, that is, consists of liquid (melted) rock matter. The high density of both sections of earth’s core support the notion that they are composed of iron and nickel.[pic 1]

[pic 2]

MANTLE

With a thickness of approximately 2885 kilometers (1800 mi) and representing n early two thirds of Earth’s mass, the mantle is the largest of Earth’s interior zones. Earthquake waves that pass through the mantle indicate that it is composed of solid rock matter, in contrast to the molten outer core that lies beneath it. Scientist agree that the mantle consist of silicate rocks (high in silicon and oxygen) that also contain significant amounts of iron and magnesium.

The interface between the mantle and the overlying crust is marked by a significant change of density, called a discontinuity, which is indicated by an abrupt decrease in the velocity of seismic waves as they travel io through this internal boundary. Scientists call this zone the Mohorovicic discontinuity, or Mohofor short, after Croatian geophysicist who first detected it in 1909. The Moho does not lie at a constant depth but generally mirrors the surface topography, being deepest under mountain ranges where the crust is thick and rising to within 8 kilometers (5 mi) of the thin ocean floor.

CRUST

• Earth’s solid exterior is the crust, which is composed of a great variety of rock types that respond in diverse ways and at varying rates to surface processes.
• As the outermost layer of the solid earth, crust comprises the ocean floor and the continents and is primary importance in understanding surface processes and landforms.
• Two kinds of earth crust; oceanic and continental and distinguished by their location, thickness, and composition.
• Crustal thickness varies from 3 to 5km (2-3 miles) in the ocean basins to as much as 70km (44miles) under some continental mountain systems
• Oceanic crust is composed of basalt, a heavy, dark colored, iron rich rock that is also high in silicon (Si) and Magnesium (Mg). It has density of 3.0g/ and is only a few kilometers thick.[pic 3]
• Continental crust comprises the major landmasses on earth that are exposed to the atmosphere. Its density is 2.7g/ lesser than the average density of oceanic crust. But it’s thicker than oceanic crust from about 20 – 70 Km with an average thickness of 32 to 40 km.[pic 4]
• Continental crust contains more light- colored rocks than oceanic crust does and can be regarded as granitic in composition.

[pic 5]

Lithosphere and Asthenosphere

• Lithosphere is the uppermost mantle and overlying crust form a single structural unit. The term lithosphere is traditionally been used to describe the entire solid earth.
• Asthenosphere(from Greek: asthenias, without strength), a 180 kilometer(110mi) thick layer of the upper mantle that responds to stress by deforming and flowing slowly rather than by fracturing. It has the characteristics of a plastic solid.
• As material in the asthenosphere flows, it drags segment of the overlying, rigid lithospherealong with it. Tectonic forces, large scale forces that break he deform earth’s crust, sometimes resulting in earthquake and often responsible for mountain building, comes from movement within the plastic asthenosphere.
• A cross section of the lithosphere and asthenosphere and extending lower into mantle.
• Turn is produced by thermal convection currents in the rest of the mantle below the asthenosphere that are driven by heat from decaying radioactive materials in the planet’s interior.

[pic 6]

MINERALS

• Is an inorganic, naturally occurring, crystalline substance represented by a specific chemical formula.

• Mineral halite, which is used as table salt, has specific chemical formula NaCl and as a crystal adopts a cubic form.
• Some examples of a minerala are quartz,calcite,fluorite,talc, topaz and diamond.
• In every mineral had distinctive and recognizable physical characteristics aid in its identification.
• Some of the characteristics include hardness,color,luster,cleavage, tendency to fracture, and specific gravity.
• Molecules and atom are the chemical bond which hold together to composed a mineral.

[pic 7]

ROCKS

• Is a consolidated aggregate of various types of minerals, OE a consolidated aggregate of multiple individual pieces (grains) of the same kind of mineral?
• Rocks are the fundamental building materials of the lithosphere.
• Rocks are weathered and eroded to the deposited as sediment elsewhere.
• A mass of consolidated rock that has not been weathered is termed bedrock

Igneous Rocks

Igneous Rocks are  formed by crystallization from a liquid, or magma. They include two types  

• Volcanic or extrusive  igneous rocks form when the magma cools and crystallizes on the surface of the Earth
• Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the Earth

Magmas are less dense than surrounding rocks, and will therefore move upward. If magma makes it to the surface it will erupt and later crystallize to form an extrusive or volcanic rock. If it crystallizes before it reaches the surface it will form an igneous rock at depth called a plutonic or intrusive igneous rock.