The Earth System

How old is Earth? 4.56 billion years Earth radius: 6400km

Earth’s topography is measured with respect to sea level.

Earth’s layered structure: Inner core, Outer core, Mantle, Crust. Inner Core: Solid iron-nickel alloy Outer core: Liquid, metallic region Mantle: Mesosphere, Asthenosphere

o Asthenosphere: Can bend like plastic Crust: thinnest layer of the Earth Lithosphere: includes the crust and upper mantle

o Forms relatively cool, brittle plates of plate tectonicso Continental Crust: 35km thicko Oceanic Crust: 5km thicko Continental crust is thicker and has a lower density than oceanic crust

CC ride higher

James Hutton- Principle of Uniformitarianism: “the present is the key to the past”.o Sand rolling along a stream bottom shows that the sediment is moving

downstream.

Crustal rocks are less dense than mantle rocks.

Convection in Earth’s mantle o Outer Coreo Hot matter from the mantle rises Plates to form and diverge

Plates convergeCooled plate is dragged under the neighboring platesinksrepeat

3.8 billion years ago: Liquid water exist 600 million years ago: Earliest land animals 65 million years ago: dinosaurs extinct

Plate tectonics

13 major plates Singapore located on Eurasian plate Active mountain belts are most likely to be found along the margins of continents

Convergent : Subductiono Deep-sea trenches, earthquake belts, mountain, volcanoes

Divergento Volcanic activity, earthquakes at the crest of mid-ocean ridge

Transform: Slidingo Linear topography, earthquake activity, offsets in magnetic anomaly

bands

Age of seaflooro Measure the age by comparing magnetic anomaly bands mapped on the

seafloor with the sequence of magnetic reversals worked out on land

Convection:o Whole-mantle convection

Minerals

Mineralso Naturally occurring, solid crystalline substance, generally inorganic, with a

specific chemical composition

Most common Earth anion: Oxygen Anions tend to be larger than cations Polymorphs: Alternative structures formed from the same chemical compound

o Eg. Graphite and diamond

Minerals group into 7 classes:1. Native Elements2. Oxides* and hydroxides

Hematite, Spinel3. Halides

Halide, table salt – NaCl4. Carbonates*

Calcite, Dolomiteo Acid Test: Calcite – fizzes and release CO2

5. Sulfates* Anhydrite, Gypsum

6. Sulfides* Pyrite (fool’s gold)

7. Silicates* Ferromagnesian/ Felsic : Containing Fe & Mg

o Amphiboles, pyroxenes, biotite mica, olivine Non-ferromagnesian/ Mafic

o Feldspars: orthoclase and plagioclase, quartz, muscovite mica

* 5 most common classes, largest group is silicate minerals

Physical Properties:1. Hardness

Talc (1) Diamond (10)2. Cleavage

Tendency of crystal to break along flat planar surfaces3. Luster

Reflect light4. Color

Imparted by light Impurities produces intense color

5. Streak Fine deposit of mineral dust left on an abrasive surface

6. Density7. Crystal habit8. Fracture

Muscovite vs Biotite1. Similarities

Both members of mica familyHave sheet structure excellent cleavage in one direction

2. Differences Light color and pearly luster vs shiny black appearance

Non-ferromagnesian vs Ferromagnesian Orthoclase vs Plagioclase

1. Similarities Both members of feldspars family

2. Differences K ions rich vs Na and Ca ions rich Light cream to salmon pink vs White to medium gray Striations absent vs Striations on cleavage faces

Igneous Rocks

Extrusive pyroclastso Form in violent eruptions from lava thrown high in the air

Extrusive Igneous rocks o Cool rapidly on Earth’s surface Fine-grainedo Mafic – Basalto Felsic – Rhyolite

Intrusive Igneous rockso Cool slowly in Earth’s interior Large, Coarse-grainedo Mafic—Gabbroo Felsic—Granite

Intrusive Porphyritico Beneath Earth’s surfaceo Some crystals grow large, but the remaining melt cools faster, forming

smaller crystals

Igneous rocks are classified based on:o Texture : size, shape and arrangement of the crystals

Affected greatly by rate of coolingo Mineral composition

Phaneritic Textureo Coarse-grainedo Individual minerals can be identified with unaided eyeo Inter-grown crystals are roughly equal in sizeo Large masses of magma solidify at deptho Eg. Felsic: Graphite – Quartz, Hornblende, Feldspar

Aphanitic Textureo Fine-grainedo Formed at the surface, or within the upper crusto Grains too small to be identified by unaided eye

Vesicular Textureo Contain voids – left by gas bubbles that escape as lava solidifieso Form near the surface of lava flowso Eg. Scoria

Porphyritic Textureo Large crystals—phenocrysts, embedded in a matrix of smaller crystals—

groundmasso Coarse grained formed first, followed by smaller

Bowen’s reaction serieso Shows the sequence in which minerals crystallize from a magmao Provides a model of fractional crystallizationo Explains the composition of basaltic intrusion that forms the palisades o Olivine crystalize earlyo The last minerals to crystallize on Bowen's Reaction Series are those

found in igneous rocks with a felsic composition.

Intrusive igneous bodies: o Plutons

Largest: Batholiths – thick horizontal masses extending from a funnel-shaped central region

Smaller: Stocks o Sills

Parallel to the layers of bedded country rockso Dikes

Cut through country rockso Veins

Form where water is abundant Either in magma or in surrounding country rocks

Sedimentary Rocks

Major process that forms sedimentary rocks:o Weathering – breaks down rocks physically and chemicallyo Erosion – carries away particleso Transportation – via water, glaciers, wind

Abrasion reduces the size and angularity of clastic particles Particles more rounded and slightly smaller

o Deposition – occurs when particles settle out or dissolved minerals precipitate

o Burial – occurs as layers of sediment accumulate and compact previous layers

o Diagenesis – involves pressure, heat and chemical reaction, lithifies (compact & cementation) the sediment to make sedimentary rocks

Factors interact to create sedimentary environments

Sedimentary basins are formed by plate separationo Earth’s primary sources of oil and natural gas

Major types of sediments and sedimentary rockso Siliciclastic sediments (detrital)

Form from fragmentation of parent rock by physical and chemical weathering and are transported to sedimentary basins by water, wind or ice

o Chemical and biological sediments Originate from minerals dissolved in and transported by water Through chemical and biological reactions, there minerals are

precipitated from solution to form sediments Clastic Sediments and Sedimentary rocks classified by:

o Particle size

o Mineral composition

Metamorphic Rocks

Metamorphism takes place when preexisting rock is changed when subjected to temperatures and pressures unlike those which it was formed.

Subjected to differential stress, some minerals will recrystallize with a preferred orientation

Regional metamorphismo Rocks over large areas are metamorphosed by high temperature and

pressures generated during mountain buildingo Changes rock texture

Contact metamorphismo Country rock close to an igneous intrusion is transformed by the heat of

the intruding magmao Source of heat: heat from nearby magma body

Seafloor metamorphism o Hot fluids percolate through and metamorphose oceanic crust

Burial metamorphismo Deeply buried sedimentary rocks are altered by pressures and

temperatures higher than those that result in diagenesis High-pressure and ultra-high-pressure metamorphism

o At great depts., as when sediments are subducted Shock metamorphism

o Meteorite impacts

Degree of metamorphism is reflected on rock’s texture and/or mineral compositiono Low-grade

More compact more denseSoft sedimentary rock hard, compact metamorphic rock

o More extreme Recrystallize to form large crystals

Microscopic clay minerals tiny mica larger mica

Classification of metamorphic rocks by Texture o Foliated rocks, Granoblastic (non-foliated) rocks

Foliated rockso Any planar arrangement of platy and elongated mineral grains or

structural features within a rocko Classified by metamorphic grade, grain size, type of foliation, bandingo Common foliated metamorphic rocks include:

(In increasing grain size order) Slate

- Low-grade metamorphic rock- Forms from shale and mudstone- Rock cleavage is common- Sedimentary features may be visible

Phyllite- Fine-grained- Formed from mudstone and shale

Schists- Formed at the highest grade of regional

metamorphism Gneiss

o Distinguished by: Slaty cleavage

- Parallel arrangement of fine-grained metamorphic minerals

- Consists of closely spaced planar surfaces along which rocks split into thin, tabular slabs when hit with hammer

Schistocity- Coarser-grained metamorphic rocks- Parallel arrangement of platy minerals such as micas

Gneissic texture- Dark and light silicate minerals have separated

banded appearance

Hornfels – forms by contact metamorphism of mudstones and shales Marble – non foliated metamorphic rock consisting mostly of calcite.