ISNS 3359 Earthquakes and Volcanoes (aka shake and bake)

ISNS 3359 Earthquakes and VolcanoesISNS 3359 Earthquakes and Volcanoes(aka shake and bake)(aka shake and bake)

Lecture 2: Matter, earth and sources of energy

Fall 2005

How We Understand the Earth• Must think in terms of geologic time rather than human

time – thousands, millions and billions of years• In 1788, Hutton introduced concept of geologic time:

– “No vestige of a beginning, no prospect of an end.”– Everyday changes over millions of years add up to major

results• UniformitarianismUniformitarianism: natural laws are uniform through

time and space; present is the key to the past• Contrast to previously believed catastrophismcatastrophism• Currently modified actualismactualism: rates of Earth processes

can vary

Energy SourcesFour primary energy sources fuel Earth processes:• Impact of extraterrestrial bodies

– Asteroids and comets; abundant in early Earth history, rare now• Gravity

– Mass of Earth pulls objects (glaciers, hillsides) downhill• Earth’s internal heat

– As Earth cools, heat flows from interior to surface– Volcanic eruptions, earthquakes– Plate tectonics; formation of continents, atmosphere and oceans

• The Sun– Evaporation of water into atmosphere produces weather– Hailstorms, lightning, tornadoes and hurricanes

Energy SourcesEnergy Sources

http://www.nikhef.nl/~pieth/astro/ph/clavius.htm

http://3dnworld.com/users/1/images/UltimateEarth.jpg

Origin of the Solar System• Solar system began as rotating spherical cloud of gas, ice, dust

and debris• Gravitational attraction brought particles together into bigger and

bigger particles• Cloud contracted, sped up and flattened into disk

Origin of the Solar System• Formation of Sun

– Greatest accumulation of matter (H and He) at center of disk– Temperature at center increased to 1 million degrees centigrade – Nuclear fusion of hydrogen (H) and helium (He) began,

producing solar radiation

Origin of the Sun and Planets• Formation of planets

– Rings of concentrated matter formed within disk– Particles within rings continued to collide to form planets – Inner planets (Mercury, Venus, Earth and Mars) lost much gas

and liquid to solar radiation, becoming rocky (terrestrial)– Outer planets retained gas and liquid, as gas planets

• Impact origin of the Moon– Early impact of Mars-sized body with Earth– Impact generated massive cloud of dust (from Earth’s crust and

mantle) and gas which condensed to form Moon– Lightweight gases and liquids lost to space– Lesser abundance of iron (from Earth’s core) in Moon

Earth History• Earth began as aggregating mass of particles and gases

– Aggregation took 30 to 100 million years

– Occurred about 4.57 billion years ago

• Process of aggregation created huge amounts of heat

• As temperature rose above 1,000 centigrade, iron melted

– Liquid iron is denser than remaining rock,

• so sank toward center of Earth to form inner and outer core

– Release of gravitational energy produced additional heat

– Remaining rock melted, • allowing low-density material

to rise– Low-density material formed

crust, oceans and atmosphere

Earth History• 3.9 billion years ago: large oceans, small continents• 3.5 billion years ago: life (photosynthetic bacteria)• 2.5 billion years ago: large continent• 1.5 billion years ago: plate tectonics

• This last point - actually a very interesting debate ==> concept of uniformitarianism and how far back does it apply

Earth HistoryAnalogy with Mother Earth, 46-year-old woman:

(1 Mother Earth year = 100 million geologic years)• First seven years unaccounted for• 42 years old: life appeared on continents• 45 years old: flowering plants• 8 months ago: dinosaurs died out• Last week: human ancestors evolved• Yesterday: humans evolved• Last hour: discovered agriculture, settled down• 1 minute ago: Industrial Revolution

The Layered Earth• Differentiated into layers of increasing density• Center of Earth: Iron-rich corecore

– Inner core is solid– Outer core is liquid and has viscous convection currents,

responsible for Earth’s magnetic field• Surrounding core is Earth’s mantlemantle, 2,900 km thick

– Stony in composition (like chondritic meteorites)• Low-density elements extracted over time (mainly through volcanic

activity) from the mantle to form the crust, atmosphere and oceanscrust, atmosphere and oceans

The Layered Earth

http://wapi.isu.edu/Geo_Pgt/Mod04_Earth/EarthFig2.htm

Lithosphere = crust + rigid part of upper mantle

Mantle convection

Driving force of plate tectonics

Behavior of Materials• Gas, solid and liquid are obvious terms, but

should be considered with respect to time– Over longer time periods, solids may

behave as liquid• Glacier is solid ice, yet flows downhill as

ultrahigh viscosity liquid over time span of years

• Elastic deformation is recoverable – object returns to original shape

• Ductile deformation is permanent – stress applied over long time and/or at high temperatures

• Brittle deformation is permanent – stress applied very quickly to shatter or break object

The Layered Earth• Asthenosphere is plastic

– “Possession of a structure weak enough to yield to an influence, but strong enough not to yield all at once”

• About 250 km thick• Comes to surface at mid-ocean ridges (and other basaltic

volcanoes)• Lies more than 100 km below surface elsewhere• Allows Earth to be oblate spheroid (flattened during

rotation; like Solar System during formation)• Allows continents to ‘float’ atop the mantle, by principles

of isostasy

Isostasy• IsostasyIsostasy: Less dense materials float on top of more dense materials

(i.e. iceberg floating in ocean)• Earth is a series of density-stratified layers• Core – densities up to 16 g/cm3

• Mantle – densities from 5.7 to 3.3 g/cm3

• Continents (crust) – densities around 2.7 g/cm3

• Oceans – densities around 1.03 g/cm3

• Atmosphere – least dense

Isostasy

Examples of isostasy:• Impoundment of water in Lake Mead behind Hoover

Dam caused area to sink 175 mm over 15 years• Scandinavia is currently rising (about 200 m so far)

– Had been depressed under weight of ice sheets during last glacial period (since 10,000 years ago)

– Ground ruptures and earthquakes are present– Viking ship buried in the harbor mud of Stockholm was

lifted above sea level– Another 200 m of uplift is likely

http://www.uwgb.edu/dutchs/EarthSC202Notes/folds.htm

http://www.museum.state.il.us/exhibits/larson/glaciers.html

Energy, Force, Work, Power and Heat• Energy: Capacity to do work

– Potential energy: potential to do work (PE = mgh)– Kinetic energy: energy of motion (KE = ½ mv2)-related to heat

• Work: Force times distance (W = Fd = mad)• Force: Mass times acceleration (F = ma)• Power: Rate at which work occurs (P = W/T)• Heat: Capacity to raise the temperature of a mass

(energy)

m (mass), g (gravity), h (height), v (velocity), a (acceleration), d (distance)

Internal Sources of Energy• Impact energy

– Tremendous numbers of smaller bodies hit the Earth early after its formation, converting energy of motion to heat

• Gravitational energy – As Earth pulled to smaller and denser mass, gravitational

energy was released as heat

Heat from both of these early sources is still flowing to the surface today, as heat conducts very slowly through rock

Also, loss of heat through advection - hydrothermal circulation at the mid-ocean ridges

Gravity• Gravity is attraction between objects:

– Two bodies attract each other with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them along with a constant (Universal gravitational constant G)

• F= GMm/(dist)2

– I worked on a project to show it is not a constant • Planetary mass can be considered concentrated at its center• Gravity of a sphere same as a particle of infinite mass at the center—can’t tell the

difference

• Gravitational effects of Sun and Moon on Earth– Moon’s mass is about 1/80 of Earth– Sun’s mass is 332,000 times that of Earth– Moon is 386,000 km from Earth– Sun is 150,000,000 km from Earth– Sun’s gravitational pull on Earth is 170 times that of the Moon

Gravity•Tidal energy is generated by interactions of gravity between Earth, Sun and Moon

•Tides are caused by differences in gravitational pull from one part of Earth to another

–Sun’s pull in mostly uniform throughout Earth, so small tides

–Moon’s pull is much greater on facing side than on opposite side, so Moon tides are about twicetwice magnitude of Sun’s tides

Gravity• Tides affect land, water and air – most obvious in ocean• Moon’s tidal bulges move relative to Sun’s tidal bulges

– Both tides coincide twice monthly (spring vs neap tides)• Tidal motions within the Earth cause:

– Earth’s and Moon’s rotations to slow down– Earth and Moon to move farther apart– Days become longer– Years have fewer days

• 370 million years ago, Earth day was 22 hours and year had 400 days

Internal Sources of EnergyRadioactive elements• Unstable radioactive atoms decay and release heat• Early Earth had much larger amount of short-lived radioactive

elements and therefore much greater heat production than now• Radioactive decay process:

– Measured by half-life: length of time for half the present number of atoms of a radioactive element (parent) to disintegrate to decay (daughter) product

– Half-lives against time is negative exponential curve

Internal Structure of Atom Internal Structure of Atom (brief and simple)(brief and simple)

• Atom = protons, neutrons, electrons (p + n = nucleons).

• Composition of an atom is expressed as the number of protons and neutrons in the nucleus. The number of protons is the atomic number (Z) and defines the location on the periodic table. N = number of neutrons and A = Z+N = mass number.

• Nuclide = atom with a unique number of protons and neutrons. Can thus define a nuclide by specifying Z and A e.g.:

Table of isotopes:

Internal Structure of Atom Internal Structure of Atom (brief and simple)(brief and simple)

Internal Structure of Atom Internal Structure of Atom (brief and simple)(brief and simple)

Internal Structure of Atom Internal Structure of Atom (brief and very (brief and very simple)simple)

Radioactive decay can be used to date rocks. Longer the half life the older the rocks can

be dated.

Internal Structure of Atom Internal Structure of Atom (brief and simple)(brief and simple)

• Isotopes of an element - same # of protons (Z) but different # of neutrons (N) i.e., same atomic number, diff. atomic weights

•Mass of proton = 1.6726231 x 10-27 kg

•Mass of neutron = 1.6749286 x 10-27 kg

•Mass of electron = 0.91093897 x 10-30 kg

• Stable isotopes = if not involved in radioactive decay scheme

• Radiogenic isotope = if formed by decay but not involved in a decay scheme

• Radioactive isotope = if undergoes radioactive decay

Internal Sources of Energy• Sum of internal energy from impacts, gravity and

radioactive elements (plus tidal friction energy) is very large

• Internal temperatures have been declining since early Earth maximum, but still significant enough to cause plate tectonics, earthquakes and volcanic eruptions

Age of the Earth• Oldest Solar System materials are 4.57 billion years

old– Measured using radioactive elements in Moon rocks and

meteorites• Oldest Earth rocks (found in northwest Canada) are

4.055 billion years old• Oldest Earth materials (zircon grains from Australian

sandstone) are 4.4 billion years old

http://www.geology.wisc.edu/zircon/Earliest%20Piece/Earliest.html

Age of the Earth

http://www.geology.wisc.edu/zircon/Earliest%20Piece/Earliest.html

Age of the Earth• Earth must be younger than 4.57 billion years old

materials that formed the planet– Seems that Earth has existed as coherent mass since about 4.54

billion years ago– Probably took 30 million years (0.03 billion years) for Earth to

form– NOTE; new estimates for gas giants (Jupiter and Saturn) - may be

as little as a few hundred years• Collision that formed the Moon seems to have occurred

between 4.537 and 4.533 billion years ago• Earth must be older than 4.4 billion years old zircons

(which indicate low T surface conditions of formation)

Radioactivity Disasters• Chernobyl disaster of 1986, in Ukraine

– Explosion released 185 million curies of radioactive atoms affecting everyone from Scandinavia to Greece

– 31 workers were killed and 165,000 later deaths blamed on accident, with more to come

• Can such a thing occur in nature? Depends on relative amounts of U-238 and U-235:– U-235 makes up 0.7% of uranium ore– Uranium ore used in reactors is enriched to 2-4% U-235– Because U-235 decays more rapidly than U-238, at some point

in the past all uranium ore would have had about 2-4% U-235– Sites in West Africa were natural nuclear reactors about 2

billion years ago, at about 400 degrees centigrade temperatures

External Sources of EnergyAll sources of internal heat flow on Earth are dwarfed by 5,300

times greater heat flow to Earth from SunSun• Solar radiation:

–43% visible wavelengths–49% near-infrared wavelengths–7% ultraviolet wavelengths–Short wavelength

• Sun’s energy:–30% reflected back to space at short wavelengths (albedo)–47% absorbed as heat–23% evaporates water and begins hydrologic cycle

Hydrologic Cycle• Sun’s heat evaporates water and plants transpire water into atmosphere• Atmospheric moisture condenses and precipitates• Sun’s energy is stored in water and water vapor• Equatorial regions receive excess insolation (solar radiation), whereas in polar

regions radiation back to space exceeds insolation• Imbalance between equatorial and polar regions cause ocean currents and winds,

transferring heat

Hydrologic Cycle• 97.1% of Earth’s water is in oceans• Of remaining 2.9%:

– 68% in glaciers– 21% underground– 10% in atmosphere– 1% in rivers, lakes, inland seas and soil moisture

• Water in atmosphere holds, transports and releases solar energy, distributing heat around the Earth

Water – The Most Peculiar Substance on Earth?

• Present in liquid, solid and gas states• Highest heat capacity except liquid ammonia• Highest heat conduction• Highest latent heat of vaporization• Highest latent heat of fusion except ammonia• Bipolar molecule easily able to bond with ions• Highest dielectric constant of liquids• Expands 9% when frozen (most substances shrink)

Processes of Construction vs. DestructionRock Cycle:• Internal heat melts rock to magma,

which rises and cools to form igneous rocks– Process of Construction

• External heat from Sun drives hydrologic cycle that weathers and erodes rocks into sediments, which are transported and deposited – Process of Destruction

Processes of Construction vs. DestructionRock Cycle:• Continents could be eroded to sea level in 45 million

years (1% Earth history), but processes of construction keep raising continents and forming new landmasses

• The power of these Processes of Construction and Destruction causes disastersdisasters!

Impacts with Asteroids and CometsEarth travels 950 million km around the Sun each year with an orbital speed of

108,000 km/hr kinetic energy = 2.7 x 1033 joules• When this kinetic energy is brought into collision with another body, effects are

catastrophic and worldwide:– Asteroid: 65,000 km/hr– Comet: 150,000 km/hr

• Additional sources of energy are:– Daily rotational motions of Earth on axis– Monthly rotational motions of Earth-Moon system about center of gravity

Volcanoes and the Origin of the Ocean, Atmospheres and Life

• Volcanic gases (H, O, S, C, Cl etc) combine to make:– Water (H2O), carbon dioxide (CO2), sulfur dioxide (SO2),

hydrogen sulfide (H2S), carbon monoxide (CO), nitrogen (N2), hydrogen (H2), hydrochloric acid (HCl), methane (CH4), and others

• Dominant volcanic gas is water vapor – more than 90%• Are volcanoes responsible for the oceans?

Volcanoes and the Origin of the Ocean, Atmospheres and Life

• Volcanic rocks:– Oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium

(Ca), magnesium (Mg), sodium (Na), potassium (K)• 4.5 billion years of volcanism has brought light weight

elements to the surface to make up – Continents– Oceans– Atmosphere– CHON (carbon, hydrogen, oxygen, nitrogen) elements of life

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