 Rudimentary Aspects of Geology (before we proceed):

INTRODUCING THE EARTH

Present Earth:

The Earth is roughly 4.5 BY old, consist of three principal solid layers:

Mantle plus Crust – 2885 km (Crust – 40 km;

Young Oceanic 4 (<200 my), Continental – 35-40 km (<3.8 BY)

Core - 3486 km (solid inner core – 1216; outer core 2270)

Outer skin – atmosphere, hydrosphere, biosphere

Review: Big Bang, Origin of Planets (Universal Calendar)

If the Earth was formed as a homogenous mass, why is it layered now. Why do we have various spheres?

Earth must have differentiated. Why and how ??

Imagine the homogeneously accreting Earth. We think it warmed up substantially (1200 deg-C), and the surface may have completely melted (dynamic argument and moon melted).

Even if it did not melt, mechanical properties must have been less rigid than now. Dense parts sink, less dense parts float. Magma rises, magma gases rises, and Fe-Ni metal sink.

Core segregated. Releasing further heat (conservation of energy).

Other sources of heat, e.g., accretion energy, radioactive decay

Solid Earth (BASICS):

The solid earth consists of ROCKS. Core – Fe-Ni alloy, Rest – silicates

Rocks consists of MINERALS, the building blocks of the Earth.

Whereas there are over 3000 known minerals, only about 2-3 dozen are common rock-forming (let me know if I had mentioned more than three dozens in the course of this semester).

Minerals are generally classified according to the anionic group present:

Native elements

Sulfides

Oxides/hydroxides

Halides

Carbonates

Sulfates

Phosphates

Silicates

The BULK SOLID EARTH consists primarily of (by weight):

Iron	35 %
Oxygen	30 %
Silicon	15 %
Magnesium	13 %
Nickel	2.4 %
Sulfur	1.9 %
Calcium	1.1 %
Aluminum	1.1 %
Sodium	0.57 %
Potassium	0.07
Others	< 1 %

The core had attracted the siderophiles; Fe, Ni, S

The mantle and crust tended to attract the lithophiles: Fe, Si, Mg, Al

The mantle (most of the silicate part of the Earth) is largely composed of O – 44%; Fe – 10%, Si – 23 %, and Mg – 19%: Fe-Mg Silicates

Due to magmatic/volcanic processes, the Crust tended to concentrate the light elements, K, Na, Al – hence K-Na-Al silicates are stabilized in the crust.

ROCKS

Igneous – mineral crystals or glass formed from solidified molten magma

Sedimentary – consolidation of loose grains or sediments or chemically precipitated from water (or by wind and other transport medium – glacier)

Metamorphic - solid-state transformation of pre-existing rocks through pressure and temperature causing recrystallization.

Rock cycle:

Metamorphic

// \\

Igneous -------------------------à Sedimentary

EROSION and WEATHERING

Weathering is the process of physically and chemically disintegrating solid rocks leading to the formation of soil, sediments and dissolved matter.

- the physical and chemical disintegration of geological deposits

- key is that the present conditions are quite different from

previous conditions - chemical and physical adjustment

Weathering reaction rates are influenced by:

(1) nature of the minerals - Reversed Bowen

(2) climate, microclimate, drainage

(3) rock textures and structures - rates in cm/year if water gets

there.

(4) biology (!)

Soils: Soil is formed by weathering of rocks. It is distinct from sediments, which are transported unconsolidated materials.

Examples:

- Podzol (New York)

- Terra rossa (limestone, residual clay, chert, sand residue)

- Laterites

Caliche - CaSO₄, CaCO₃ in arid climate

PLATE TECTONICS and TECTONIC SETTINGS

This is a true UNIFYING theory for Earth Sciences

Alfred Wegener: 1915 outlined the idea of movement of the continents

SUPPORT:

Fit of Coastlines:

Fossil Evidence

Paleoclimate

Magnetic Evidence Earth's magnetic field is like that produced by a bar magnet.

The magnetic field can be recorded in rocks when they are formed. The "mineral magnets" will point toward poles by virtue of their magnetism.

ATMOSPHERE AND OCEANS (COMPOSITION/STRUCTURE)

(to be continued)