2 energy and environment 2

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Energy and Environment

EN3

Lecture 2

Dr. Mamta Awasthi

CEE, NIT


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Introduction

Today we start into our review of the history of Life

We will look at the origins of the earth and its features thatmay have made it suitable for life.

The layers of atmosphere

Key Points

Earth and the Solar System formed at the same timeapproximately 4.6 Billion Years ago.

The earth's size and position made it suitable for life todevelop.

Life probably originated around 3.8 billion years ago. The origins of the Universe

Layers of the atmosphere


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Origin of Earth

Earth, along with the other planets, is believed to havebeen born 4.5 billion years ago as a solidified cloud ofdust and gases left over from the creation of the Sun.

For perhaps 500 million years, the interior of Earthstayed solid and relatively cool, perhaps 2000F.

The main ingredients, according to the best availableevidence, were iron and silicates, with small amountsof other elements, some of them radioactive.

As millions of years passed, energy released by

radioactive decaymostly of uranium, thorium, andpotassiumgradually heated Earth, melting some ofits constituents.

The iron melted before the silicates, and, being heavier,sank toward the center. This forced up the silicates that

it found there.


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After many years, the iron reached the center, almost4,000 mi (mile) deep, and began to accumulate.

No eyes were around at that time to view the turmoil thatmust have taken place on the face of Earthgiganticheaves and bubblings on the surface, exploding volcanoes,and flowing lava covering everything in sight.

Finally, the iron in the center accumulated as the core. Around it, a thin but fairly stable crust of solid rock formed

as Earth cooled.

Depressions in the crust were natural basins in which

water, rising from the interior of the planet throughvolcanoes and fissures, collected to form the oceans.

Slowly, Earth acquired its present appearance.


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A. Nebular theory (LaPlace)

...the whole of the matter of the solar systemonce formed a globular or spheroidal mass ofintensely heated gases, extending beyond theorbit of the outermost planet, and having a slow

motion of revolution about an axis. As it cooledand contracted, its rate of revolution increased,and this became so great that at successiveepochs it threw off rings, which, owing to slight

irregularities, broke up, and, gravitating together,formed the planets. The contraction continuing,the sun, as we now see it, was the result. (A. R.Wallace, 1904, p. 112.)


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B. Planetesimal Hypothesis of

Chamberlin & Moulton:

generic condensation produces dust and

smaller bodies

formation of protoplanetary disc

"Colder" planetesimals accumulate due to

gravity

Accretion theories: updated planetesimal view


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A. Homogeneous vs. heretogeneous

accretion 1. Homogeneous accretion asserts that the accumulation of

planetisemals initially formed a well-mixed Earth thatbegan to undergo differentiation as gravitational collapseresulted in the release of heat. Convection and escape ofheat through surface begins, but as Earth gets too big,convection cannot handle heat buildup andpartialmeltingoccurs. (Partial melting is required to generate the corewithout completely melting the mantle). Fe-rich coreforms, differentiation now begins.

Hetrogenous accretion theory is the idea that the internal

layering of Earth began in time with denser, Fe-richmaterials to which were added lighter, silicates thatcompose the mantle and crust.


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The last common ancestor

When the earth formed some 4.6 billion years ago, itwas lifeless and inhospitable to living organisms.

One billion years later it was already teeming withprokaryotic life forms, ancestors to all present livingthings.

What would these early progenitors of life be like?

If we make the reasonable assumption that the lastcommon ancestor of all presently living organismsmust have had those characteristics which are now

shared by the organisms which constitute the fiveliving kingdoms, then a listing of the commoncharacteristics of living species also describes theminimum characteristics of the last common ancestor


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All life is cellular

All living things are from 50 to over 90% water,

the source of protons, hydrogen and oxygen in

photosynthesis and the solvent of biomolecules.

The major elements of covalently bound

biomolecules are carbon, hydrogen, nitrogen,oxygen, phosphorus and sulfur.

There is a universal set of small molecules: (i.e.

sugars, amino acids, nucleotides, fatty acids,phospholipids, vitamins and coenzymes.)

The principle macromolecules are proteins, lipids,

carbohydrates and nucleic acids.


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There is a universal type of membrane structure

(i.e. the lipid bilayer) The flow of energy in living things involves

formation and hydrolysis of phosphate bonds,usually ATP.

The metabolic reactions of any living species is asubset of a universal network of intermediarymetabolism (i.e. glycolysis; the Krebs cycle, theelectron transport chain)

Every replicating cell has a genome made of DNAthat stores the genetic information of the cellwhich is read out in sequences of RNA andtranslated into protein.


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Biologists and paleontologists have

defined five basic questions that need

to be answered when discussing the

origin of life

(1) Where did the raw materials for life comefrom?

(2) How did monomers develop?

(3) How did polymers develop?(4) How did an isolated cell form?

(5) How did reproduction begin?


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The extraterrestrial origin of life?

Svante Arrhenius in 1908 proposed the"panspermia theory" - that life originated onEarth with the arrival of spores that had drifted

through space from some other planetary orsolar system.

Among those who favor this hypothesis, FrancisCrick argues that the overwhelming biochemical

and molecular evidence suggests that the lastcommon ancestor was already on earth 3.5 to3.6 billion years ago when the history of lifebegan on earth.


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Is the Panspermia idea a viable one?

The possibility that life once existed on Mars made muchnews last year.

The evidence is questionable but still a possibility.

Is it likely that microbial life came to earth from Mars or somemore distant extraterrestrial source?

"Deinococcus radiodurans, a bacterium highly resistant toradiation, would be a good vector for panspermia, said Dr.[Kenneth W.] Minton [of the Uniformed Services Universityof Health Sciences in Bethesda, MD].

While drifting through interstellar space for many thousands

of years, it might acquire a shell of interstellar crud thatcould protect it [from the intense heat generated] when itentered some planets atmosphere space"


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Layers of the atmosphere


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Troposphere

Troposphere. (0 km to 10 km) The lowest shell is theregion of water vapor, clouds, and all of our weather.

It extends from sea level up to about 18 km at theequator or about 8 km at the poles. This is a zone of

turbulence and rapid mixing. Localized surface heating, topographic rises, and water

phase changes, all cause significant changes inatmospheric temperature and pressure called

weather. However, the most significant effects areprimarily due to gravity. Because of this, thetemperature, pressure, and density generally decreasewith altitude.


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Stratosphere

Stratosphere. (10 km to 50 km) This is the layerabove almost all water vapor where thetemperature rapidly increases with altitude.

Here the density is low enough that direct

heating by light from the sun is much moresignificant than conduction or convection frombelow as it was for air in the troposphere.

This makes it vertically stable and "stratified",hence the name. This is the zone where most ofour protective ozone layer resides. Thisstratosphere extends up to about 50 km.


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Mesosphere and Ionosphere

Mesosphere. (50 km to 80 km) This is the

"middle sphere". Here the temperature again

decrease with altitude This is the zone where

most of our protective ozone layer is produced

by ionizing solar and cosmic radiation. Themesosphere extends up to about 80 km.

Ionosphere. Above about 80 km, most of the

particles are ionized by high-energy light fromthe Sun as well as cosmic rays. This vast region

is usually broken thermosphere, exosphere and

magnetosphere.


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Thermosphere

Thermosphere. (80 km to 700 km) The thermosphere ischaracterized by large temperature variations (> 300C).

There are very few molecules and so heat retention is verylow.

This is the region of the Low Earth Orbit, where the Space

Shuttle, the Hubble Telescope, and many earth observingsatellites reside.

By human standards, this is almost a perfectvacuum. However, the few atoms and molecules that existhere are easily ionized by sunlight and cosmic radiation.

This ionization leads to the production of the hauntinglybeautiful Aurora Borealis and Aurora Australis as well asthe so-called D, E, F1, & F2 layers that make long distanceradio communication possible by reflecting radio waves

back to earth.


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Exosphere and Magnetosphere

Exosphere. (700 km to 5000 km) The exosphere isthe zone from which atoms and molecules are

continuously escaping into space.

Magnetosphere. (5000 km to >> 60,000 km) The

outermost shell is enormous and is strongly

influenced by the interaction of Earth's magnetic

field and the solar wind. It contains the Van Allen

radiation belts where high energy chargedparticles are trapped and concentrated. This is the

region occupied by Geosynchronous Satellites.

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