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Introduction to Environmental Chemistry

1.1 Beginning of the Universe

About 13.7 billion years ago, markedly condensed neutron collection led to the beginning of the universe as a distinctive massive fireball known as the "Big Bang". As a result of this explosion, hydrogen and some helium nuclei were produced, which further produced galaxies and stars eventually. However, there are some misconceptions regarding this theory. Some experts believe that it was not an explosion but an expansion. Due to extreme density and pressure, at a finite time in the past, the expansion of the universe began. With the passage of time, this fireball cooled down and different physical processes came into play which formed the stars and galaxies we see around. Another misapprehension regarding the Big Bang is "singularity", according to which our universe came into existence as a little fireball emerging somewhere in space. But according to some experts, space didn't exist before the Big Bang. Back in the late 1960s and early 1970s, three British astrophysicists, Stephen Hawking, George Ellis and Roger Penrose put their attention on the theory of relativity and its consequences regarding our concepts of time. In 1968 and 1970, they prolonged Einstein's Theory of General Relativity to include measurements of time and space. Their calculations showed that time and space had finite beginning, corresponding to the origin of mass and energy. Thus, it is believed that singularity didn't appear in space; rather space arose inside of singularity, and prior to singularity, nothing existed, neither space, time, mass or energy - nothing.

Approximately 4.6 billion years ago, gravitational collapse of a gigantic molecular cloud resulted in the formation of our solar system; this is generally known as the "nebular hypothesis". Various stars, planets, galaxies and sun formed within crumpling clouds and maximum mass of solar system was gathered in the sun while the rest was flattened into a protoplanetary disc. The sun, the red giant, expanded many times before casting off its external layer, which is misleadingly called a "planetary nebula". However, this hypothesis is contradicted by a large number of alternative theories. In the 1920s, Edwin P. Hubble discovered a relationship that is now known as "Hubble's law". This law states that velocity of a galaxy is proportional to its distance from us. Hubble's law is used to determine the age of the universe by its velocity and its current distance. The time is distance divided by velocity which turns out to be one divided by Hubble's constant for all galaxies. By using the appropriate cosmological model, the calculated value is 13.73 billion years; that is quite close to the estimated answer of 14 billion years. According to Hubble's law, v = H × d where Ho = 1/t and "v" is velocity of the galaxy (in km/s), "d" is its distance (in megaparsecs,0 Mpc; 1Mpc = 3.086×1019 km), H0 is Hubble's constant and "t" is time. Background cosmic radiations were discovered in 1967 that were the strong advocate of Big Bang, and thus are considered as the second pillar of the Big Bang theory.

However, hydrogen and helium comprise only a small percentage of the total observed density of the universe and maximum mass of the universe is other than atomic matter. Due to interaction between light and matter, background cosmic radiations originated. Radiance is produced by the metals when heated at elevated temperatures. The radiations that are emitted by this material are known as "black body radiations" (BBR). The third pillar of the Big Bang theory (abundance of hydrogen and helium) states that about 90% of the universe is made of hydrogen atom and the other 10% of helium atom. In the beginning, the temperature of the universe was so hot that neutral atoms and atomic nuclei were unable to exist. The universe was a blend of particles and radiations at that time. But immediately, after two minutes, the temperature was lowered by 1 billion Kelvin (still hotter than the middle of the sun). The density of the universe was half of the density of air. At this reduced temperature, deuterium was able to hold together. The reason for this is that, at such a high temperature collision of proton with deuterium had adequate energy to break it apart. Thus from the above discussions, it has been concluded that at low temperature, matter exists in combined form while at elevated temperatures, matter is found in individual particle forms.

Plasma is the gaseous mixture of freely charged particles like electrons, protons and various other sub-atomic particles and ions that can respond to strong electromagnetic radiations. Plasma is a strong conductor of electricity due to the presence of free charges that carry electric current thereby generating a huge amount of magnetic field. This process may cause plasma to constrict into filaments, produce beam of particles, emit wide range of radiations including radio waves, light waves (including infrared, ultraviolet and visible region of electromagnetic spectrum), microwave, x-ray, gamma rays and synchrotron radiation, and form cellular regions of plasma with characteristics similar to magnetosphere and interplanetary medium. Plasma is a distinctive fourth state of matter other than pure solids, liquids and gases and known because of its unique characteristic properties. It is sometimes even referred as "first state of matter". Plasma usually appears as a cloud of natural gas or ion beam of charges that may also include grains and dust particles thereby generating "dusty plasma". Plasma is formed by heating the ionized gas by stripping electrons quite away from the atom and enabling the positive and negative charges to move freely. Plasma was first identified in a discharge tube, also known as Crookes tube, and was so described by Sir William Crookes in 1879, who called it "radiant matter".

1.2 Plank's Time

Plank's time is the time taken by a photon in travelling with the speed of light to cover the distance equal to Planck length. Plank's time is most significant in cosmology (a branch of astronomy involving the origin and evolution of the universe, from the Big Bang to today and on into the future). This extremely small time period is only about 10-43 seconds. The interaction between radiations and matter with space is described by general relativity. No theory was able to explain the universe before Planck time. In 0 to10-43 seconds: shifting of Big Bang upto Plank time occurred and no physical theory was able to explain the behaviour of matter at the beginning of the universe while looking at the history of the universe. In 10-43 to 10-35 seconds: antimatter was produced with little spare of matter during this period of time, and only a minute amount of mater was left over when matter and antimatter was annihilated. In the present time, only one baryon per billion photons is present in universe. From 10-35 to 10-6 seconds: four identifiable forces were separated from fundamental forces and Hadron and Mesons were combined at the end of that era. In between 10-6 to 10-4 seconds: a short period ranging from 10-6 to 10-4 seconds after the Big Bang when heavy weight atomic particles like protons, neutrons, pions and kaons were formed is known as the Hadron Era. Extra baryons were left over, which led to the formation of stars and galaxies after annihilation of baryons and antibaryons.

In 10-4 to 10 seconds: following the Hadron Era is the time period during which photons; neutrons, positrons and electrons were present in almost equal numbers; this is called Lepton Era. Leptons felt the weak interactions just like electrons. At about 0.1 second, n/p ratio started to slant in favor of proton. Neutrinos stopped interacting with each other and matter at about 1 second and n/p ratio was fixed, which in turn determined helium and deuterium abundance in the universe. After three to twenty minutes: nuclear fusion produced helium, deuterium and lithium. The elaboration of helium abundance was a big achievement of Big Bang theory. Furthermore, abundance of deuterium and lithium was also explained by Big Bang theory. In between 10 to 1011 seconds (approximately 3000 years (equavalent to the time on earth)), the energy density of the universe was dominated by radiations during the period called the Radiation Era. At 1013 second (400,000 years (equavalent to the time on earth)): At this time period, the temperature was very low, enabling the neutral atoms to survive individually thus becoming transparent. Then, radiations were able to cross them freely without being absorbed or scattered. From 1013 second to present: with the passage of time, the temperature of the universe decreased, eventually leading to the formation of stars, galaxies and constellations. Nuclear fusion reactions led to the formation of the first star within the first few minutes of the formation of the universe.

1.3 Components of Solar System

The aggregation of eight planets (excluding Pluto) and their moons in ellipsoidal orbits around the sun, along with smaller bodies like asteroids, meteoroids and comets is called "solar system" (Figure 1.1). Atoms, molecules and particles of cosmic dust from interplanetary clouds got attracted towards each other due to the gravitational field about 6×109 years ago and began to fall together into what is known as the "solar system". The sun is the principal source of energy for existence of life on earth. It is the...