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ORIGIN OF THE UNIVERSE & SOLAR SYSTEM

Cosmology; is the branch of astronomy involving the study of the  of the universe and the solar system. Cosmo-chemistry ;( chemical cosmology); is the study of chemical composition of the matter in the universe and the process that led to those compositions The solar system is made up of the sun (a star) with nine planets orbiting around it. These planets together with all the other heavenly bodies moving around or between individual planet form members of the solar system. Other heavenly body include; asteroids, comets, meteors, meteorites and satellites such as moon. The solar system does not include other stars .

There are two main types of planets; terrestrial (inner) planets and Jovian (outer)Planets

Origin of the solar system

Cosmologists attempt to answer the question “ the origin of the universe?”

The following theories are most commonly used to explain the evolution of the solar system

a.  Passing star theory

The theory was advanced by  Jeans and Jaffreys who .speculated that the solar system was formed about 4600 million years ago. They suggested that a star with greater gravitational pull than the sun passed close by the sun drawing off a stream of material in form of gas. These materials split, cooled and condensed to form planets set in the orbit by the passing star. The moons and other heavenly bodies moving around were thought to have formed in a similar manner

 This theory has the following major weaknesses

(a) Chances of another star approaching the sun is minimal

(b) High temperature, materials drawn from the sun or from the star would disperse rather than condense

(c) It does not explain where the sun and passing star came from

b. The Nebular theory

The solar system evolved or was formed from a rotating cloud or solar nebular of gas and dust. As the nebular rotated, it flattened into a disc with a high concentration of material at its centre. The flattening out was due to centrifugal force. In the outer sections of the disc, some substances such as methane and ammonia condensed while some like hydrogen and helium remained as gas. The outer rings formed planets like Jupiter, Saturn, Uranus and Neptune. Near the centre of the nebular, temperatures were much higher. The planets were formed by the accumulation of particles bumping into each other and growing into sizes large enough to exert gravitational attraction to each other. Continued accumulation and condensation of these gases led to the formation of other planets. At the same time, the sun continued to shed off most of its gases, hence reducing its rate of rotation to about once in 25 days. Due to high temperature, most volatile gases were probably swept away. This theory however has its own weakness e.g.  the origin and causes of the nebular are not explained

c. Big bang theory

At the beginning, the entire matter of the universe was condensed into a cloud of gas and dust. This underwent consecutive contraction and expansion and finally exploded with big bang about 6.5 billion years ago. The stellar body burst into several fragments which were thrown into space at a tremendous speed. This gave rise to the solar systems including ours. The earth’s is a tiny part of our solar system.

d. Supernova Explosion Theory

Most cosmologists believe the universe began as a dense kernel of matter and radiant energy which started to expand about 13.7 billion years ago, and later coalesced by cooling into elementary particles, atoms, stars and galaxies.

As cooling occurred, matter began to form, these atoms were pooled or attracted to one another by gravitational attraction to form  other more complex molecules ,stars and galaxies

 The elemental composition of the universe is governed by the nuclear processes of the stars. Through the process of nuclear fusion, two hydrogen atoms are squeezed together, forming a helium atom and releasing energy.   

The energy required to initiate nuclear fusion is about 108 Kelvins. (Hydrogen burning Requires 107 – 108 K) This energy an only be available when a star has a mass equal to that of our sun (called one solar mass).

Stars with larger masses generate greater internal temperatures, and are therefore able to synthesize elements heavier than helium.

Stars with 20 solar masses are capable of synthesizing all the elements through. Each step in the fusion process from helium to iron releases energy and produces a more stable nucleus. All elements after iron contain a nucleus that is less stable than the starting materials, and cannot be used to provide energy for a star.

 Elements 27 through 92 (manganese through uranium) are formed when stars exhaust their nuclear fuel, collapse in upon themselves, and then explode outward in a Super Nova explosion. The shockwave of the Super Nova explosion provides the extra energy necessary to synthesize the elements past iron.

Some of the elements formed are not stable, spontaneously decomposing to more stable substances. This process, nuclear fission, results in a release of energy and ultimately, elements that are stable. Several elements, uranium being one example, require many steps before reaching a stable state.

Since the rates of decay are well known for most heavy elements, it is possible to calculate accurate ages for substances that contain long-lived radioactive isotopes. This information has been used to estimate the age of our solar system, and its components, at 5 billion years old. The age of the universe, as determined from several astronomic measurements, is thought to be 15 billion years old. Since our sun does not possess sufficient mass to synthesize elements heavier than helium, and it is known to contain many heavy elements, we know that our solar system formed from space debris generated by earlier Super Nova explosions.

As time goes on, the elemental composition of the universe will gradually change, with hydrogen and helium being slowly converted into heavier elements. For our solar system, the chemical composition is essentially constant. This is because, in the overall scheme of things, the lifetime of our solar system is a mere blink of Father Time’s eyelid.

                  e.  Accretion of the Planets,

Cosmetologist further  believe that elements of earth were formed in stars that had lived out their life cycle, spewing out cosmic debris in the form of chemical elements. As this material drifted through space, gravitational attraction caused matter to concentrate into well defined regions. The majority of the mass was concentrated into the sun, generating enough heat to initiate the nuclear fusion process.

Planets formed from the material not included in the sun through a process called accretion. Originally proposed in 1944 by the geophysicist Otto Schmidt, the process of accretion was not proven until the Apollo lunar missions were able to return material from the surface of the moon for analysis and examination.

Accretion is a process where small dust grains become large dust grains, large dust grains become small particulates which gradually become large particulates, the large particulates become gravel which in turn becomes small balls, the small balls become large balls, which then become tiny planets. The tiny planets become larger planets, and the process continued until all matter in the region has been incorporated into a terrestrial body.

The majority of the earth’s mass was in place 4.56 billion years ago. Accretion continued to increase earth’s mass until it was large enough to retain an atmosphere (4.4 billion years ago). Heat generated, primarily from the accretion process and also  from decay of radioactive elements, caused the earth’s core to melt and initiated the geothermal cycle. This led to a differentiation of the chemical elements, first explained by Victor Goldschmidt. The oldest rocks on earth are some zircons from western Australia that are between 4.1 and 4.3 billion years old.

Primary differentiation of the elements is based on an elements chemistry relative to iron. This is reasonable since iron constitutes 35% of the earth’s mass. Four classifications of elements were established by Goldschmidt. They are:

1. Siderophiles–elements that are reduced by iron;
2. Lithophiles–elements that are not reduced by iron and have a tendency to form oxide complexes;
3. Chalophiles–elements that are not reduced by iron and have a tendency to form sulfide complexes; and
4. Atmophiles–elements that escape to the atmosphere.

The atmosphere consists of the gases that surround the earth, and its composition has changed dramatically since the earth formed. Earth’s first atmosphere was lost to space in the first million years following accretion. This atmosphere consisted of the gases locked inside the planetoids from which earth formed. Its composition was primarily carbon dioxide and nitrogen with trace amounts of methane, ammonia, sulfur dioxide and hydrochloric acid. There was no oxygen.

Earth’s second atmosphere contained carbon dioxide, nitrogen and water–and still no oxygen. As the earth surface cooled large amounts of water formed oceans and lakes, and started the hydrologic cycle–and weathering processes. The exact conditions that existed at ground level during the next two billion years are largely unknown, because the output of the sun was about 30% less than it is today and because the exact atmospheric composition isn’t known.

Photosynthetic bacteria began producing oxygen between 3.5 to 4 billion years ago, but all oxygen produced was consumed by minerals in the sea (mostly iron). Two billion years ago oxygen began entering the atmosphere, and our current atmospheric composition was reached 1.5 billion years ago.

Once in the atmosphere, oxygen reacted with incoming UV radiation to form ozone. Ozone acted as a filter against the intense solar radiation, permitting life to move from the oceans to the land.

The oldest known fossils were located in rocks that are 3.55 million years old, and were found in western Australia by J. William Schopf of UCLA. These fossils are remarkably similar to the structure of modern day cyanobacteria, highly evolved oxygen producing photosynthetic organisms.

The question of how life could spontaneously begin in such an inhospitable environment as that of the early earth was answered in 1953. Stanley Miller passed electric sparks through a mixture of water and gases similar to those thought to exist 4.5 billion years ago on earth. In a relatively short period of time, Miller was able to show that aspartic acid, glycine, a-alanine and b-alanine had been formed.

These substances are simple organic molecules essential to higher lifeforms–and they had formed spontaneously! A long list of similar molecules has been observed in interstellar space and inside meteorites. Perhaps most significant was the 1996 find of bacteria inside material believed to have originated from the surface of Mars.

                Environmental Segments:
The environment consists of various segments such as atmosphere, hydrosphere, lithosphere and biosphere. Before explaining the chemistry that is taking place in these segments one by one, a brief out line about their importance will be discussed.

Atmosphere: Atmosphere is a gaseous mixture of air that surrounds the earth. Atmosphere:
Atmosphere plays the following vital role in the survival of life in this planet.
• The atmosphere is the protective blanket of gases which is surrounding the earth. It protects the earth from the hostile environment of outer space.
• It absorbs IR radiations emitted by the sun and reemitted from the earth and thus controls the temperature of the earth.
• It allows transmission of significant amounts of radiation only in the regions of 300 – 2500 nm (near UV, Visible, and near IR) and 0.01 – 40 meters (radio waves). i.e it filters tissue damaging UV radiation below 300 nm.
• It acts as a source for CO2 for plant photosynthesis and O2 for respiration
• It acts as a source for nitrogen for nitrogen fixing bacteria and ammonia producing plants.
• The atmosphere transports water from ocean to land.

Its different layers’ areas are;

Troposphere: It is the lowest region of the atmosphere extending from earth’s surface to the lower boundary of the stratosphere. It contains water vapors and is greatly affected by air pollution.

 Stratosphere: The layer of the earth’s atmosphere above the troposphere and below the mesosphere is called stratosphere. Ozone layer to; present in this region.

 (iii) Mesosphere: it is the region of the earth’s atmosphere above the stratosphere and below the thermosphere. It is the coldest region (temperature – 2 to 92°C) of atmosphere.

Thermosphere: The upper region of the atmosphere above the mesosphere is called thermosphere. It is the hottest region (temperature up to 1200°C).

(v) Exosphere: it is the uppermost region of atmosphere. It contains atomic and ionic O2, H2 and He.

2. Hydrosphere: It is the aqueous envelop of the earth e.g., oceans. Lakes, etc.
3. Lithosphere: The solid rocky portion of the earth constitutes the lithosphere.
4. Biosphere: The biological envelop which supports the life is called biosphere e.g. animal, human beings.

The composition of the Earth’s atmosphere has been changed by human activity and some of these changes are harmful to human health, crops and ecosystems. Examples of problems which have been addressed by atmospheric chemistry include acid rain, photochemical smog and global warming. Atmospheric chemistry seeks to understand the causes of these problems, and by obtaining a theoretical understanding of them, allow possible solutions to be tested and the effects of changes in government policy evaluated.