Human Diversity

Outline of Presentation Thinking about the universe Our evolving picture of the universe Critique of pure reason The nature of a scientific theory Our modern picture of the universe Our  galaxy and the stars
Formation of solar system and the start of life on Earth Exploding Stars and Supernovae Outline of Presentation Type II Supernova Type Ia Supernova Are we stardust? The Nebular Hypothesis How First life started on Earth?

POWERPOINT 1
Title: A brief history of the universe
Thinking about the universe  
• We live in a strange and wonderful universe. Its age, size, violence, and beauty require extraordinary imagination to appreciate. Some decades ago, Bertrand Russell gave a public lecture on astronomy. He described how the earth orbits around the Sun and how the Sun, in turn, orbits around around the centre of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: «what you have told us is rubbish. The world is really a flat plate supported on the back of a giant turtle.» The scientist gave a superior smile before replying, «What is the turtle standing on?» «You are very clever, young man, very clever,» said the old lady. «but it turtles all the way down!» • Most people nowadays would find the picture of our universe as an infinite tower of turtles rather ridiculous. • If you are a regular stargazer, you have probably seen an elusive light hovering near the horizon at twilight. It is a planet, Mercury, but it is nothing like our own planet. A day on Mercury lasts for 2/3 of the planet year. Its surface reaches temperatures of over 400 degrees Celsius when the Sun is out, then falls to almost – 200 degrees Celsius in the dead of night.

• Another thing that is hard to imagine  is how far away the planets and stars really are. It is natural to think the stars and planets are much closer than they really are. In every day life we have no experience of the huge distances of space. Those distances are so large that it does not even make sense to measure them in feet or miles, the way we measure most lengths. Instead we use the light-year, which is the distance light travels in a year. In one second, a beam of light will travel 186,000 miles, so a light year is a very long distance. The nearest star other than our sun is called Proxima Centauri (Alpha Centauri C), which is about 4 light years away. • Ancient people tried to hard to understand the universe, but they had not yet developed mathematics and science. Today we have powerful technological tools like computers and telescopes. • Humans are curious species. We wonder, we seek answers. Gazing at the immense heavens above, people have always asked a multitude of questions. What do we really know about the universe? What is the nature of reality? Where did the universe come from? Where is it going? Did the universe have a beginning? and if so, what happened before then? Will it ever come to an end? • The place we humans hold within the vast cosmos seem pretty insignificant.

Our Evolving Picture of the Universe
• Around 340 B.C. , the Greek philosopher Aristotle wrote a book called “On The Heavens”, in which he made good arguments for believing that the earth was a sphere rather than flat like a plate. • On argument was based on eclipses of the moon. Aristotle realized that these eclipses were caused by the earth coming between the sun and the moon. When that happened, the earth would cast its shadow on the moon, causing the eclipse. Aristotle noticed that the earth’s shadow was always round. This is what you would expect if the earth was a sphere, but not if it was a flat disk. • The Greek had another argument for the earth being round . If the earth was flat, you would expect a ship approaching from the horizon to appear first as a tiny, featureless dot. Then, as it sailed closer, you would gradually be able to make out more detail such as its sails and hull. But that is not what happens. When a ship appears on the horizon, the first things you see are the ship’s sails. Only later do you see its hull. • The Greeks knew from their travel that the North Star appeared lower in the sky when viewed from the South than it did in more northerly regions. • Aristotle thought the earth was stationary and that the Sun, the Moon and the planets moved in circular orbits around the Sun. For mystical reasons he believed that the earth was the center of the universe and that the circular motion was the most perfect.
                    
• This idea (the earth stood at the center) was elaborated by Ptolemy in the second century AD. Earth stood at the center surrounded by 8 spheres that carried the Moon, the Sun, the Stars and 5 planets (Mercury, Venus, Mars, Jupiter and Saturn). The outermost sphere carried the fixed stars. • Another model, however, was proposed in 1514 by a Polish priest, Nicolaus Copernicus. Copernicus had the revolutionary idea not all heavenly bodies must orbit the earth. In fact, his idea was that the sun was stationary at the center of the solar system and that the earth and the planets moved in circular orbits around the sun. The real advantage of the Copernican system is that the equations of motion are much simpler in the frame of reference in which the sun is at rest. • The German Johannes Kepler and the Italian Galileo Galilei started publicly to support the Copernican theory. • In 1609, Galileo started observing the night sky with a telescope, which had just been invented. When he looked at the planet Jupiter, Galileo found that it was accompanied by several small satellites or moons that orbited around it.  This implied that everything did not have to orbit directly around the earth, as Aristotle and Ptolemy had thought. At the same time Kepler improved Copernicus’ theory, suggesting that the planets moved not in circles but in ellipses. These events were the death blows to Ptolemy’s model.
                               
• The true explanation for why the planets orbit the sun was provided only much later in 1687, when Sir Isaac Newton published his Philosophiae Principia Mathematica, probably the most important work in physical sciences. In Principia, Newton presented a law stating that all objects at rest naturally stay at rest unless a force acts upon them, and described how the effects of force cause an object to move or change an object’s motion. • According to the law of gravitational attraction “each body in the universe was attracted toward each other body by a force that was stronger the more massive the body and the closer they were to each other”. • Newton was able to show that due to the gravity of the sun, the earth and other planets should move in an ellipse_ just as Kepler had predicted. Newton claimed that his laws applied to everything in the universe, from a falling apple to the stars and planets. • Aristotle and other Greek philosophers believed that the human race and the world around it had existed, and would exist, forever.

Critique of pure reason
• Aristotle and other Greek philosophers believed that the human race and the world around it had existed, and would exist, forever. • The questions of whether the universe had a beginning in time and whether it is limited in space were later extensively examined by the philosopher Immanuel Kant in his monumental work Critique of Pure Reason, published in 1781. He called these questions antinomies (contradictions) of pure reason because he felt that there were equally compelling arguments for believing the thesis, that the universe had a beginning, and the antithesis, that it had existed forever. • His argument for the thesis was that if the universe did not have a beginning, there would be an infinite period of time before any event, which he considered absurd. The argument for the antithesis was that if the universe had a beginning, there would be an infinite period of time before it, so why should the universe begin at any one particular time. In fact, his cases for both the thesis and antithesis are really the same argument. They are both based on his unspoken assumption that time continues back forever. 
The Nature of a Scientific Theory
• In order to talk about the nature of the universe and to discuss such questions as whether it has a beginning or an end, you have to be very clear about what a scientific theory is. The simpleminded view is that a theory is just a model of the universe. A set of rules that relate quantities in the model to observations that we make. • A theory is good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations. The theory that everything was made out of four elements: earth, air, fire and water, was simple enough but did not make any definite predictions. • Newton’s theory of gravity was based on an even simpler model, in which bodies attracted each other with a force that was proportional to a quantity called their mass and inversely proportional to the square of the distance between them. Yet it predicts the motions of the sun, the moon, and the planets to a high degree of accuracy. • Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time a result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. • A good theory is characterised by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation.

Our Modern Picture of the Universe
• Our modern picture of the universe dates back only to 1924, when the American astronomer Edwin Hubble demonstrated that the Milky Way was not the only galaxy. He found, in fact, many others with vast tracks of empty space between them. • In the years following his proof of the existence of other galaxies, Hubble spent his time calculating their distances and observing their spectra. At that time most people expected the galaxies to be moving around quite randomly, and so Hubble expected to find as many blue-shifted spectra as red-shifted spectra. It was quite a surprise, therefore, to find that most galaxies appeared red-shifted: nearly all were moving away from us. • More surprising still was the finding that Hubble published in 1929: even the size of a galaxy’s red shift is not random but is directly proportional to the galaxy’s distance from us. In other words, the farther a galaxy is, the faster it is moving away ! • And that meant the universe could not be static or unchanging in size, as everyone previously had thought. It is in fact expanding; the distance between the different galaxies is growing all the time. • Hubble’s observations suggested that there was a time, called the big bang, when the universe was infinitesimally small and infinitesimally dense. Under such conditions all the laws of science and therefore all ability to predict the future, would break down. • For Hubble’s universe, an expanding universe, there may be physical reasons why there had to be a beginning. Most scientists agree that the universe must have begun with a tremendous expansion from a very hot dense state, a big bang. This is the initial formation of matter and energy and then galaxies, stars and planets.

An expanding universe
• In 1929, Hubble published his observations showing that the universe is expanding. But Hubble did not directly observe the universe expanding. He observed the light emitted by galaxies. • Light carries a characteristic signature or spectrum, based on each galaxy’s composition. By analysing the spectra of distant galaxies, Hubble was able to determine their velocities. He had expected to find as many galaxies moving away from us as moving towards us. Instead he found that nearly all galaxies were moving away from us (redshift) and the further away they were, the faster they were moving. Hubble concluded that the universe is expanding. • Astronomers can estimate the speed of recession of the distant galaxies by measuring their redshifts. A redshift is the increase in wavelength that a ray of light undergoes when its source is receding from the observer. The principle of this phenomena is the Doppler effect familiar in every day life- the change in pitch that a sound wave undergoes when a speeding train passes the observer. • In light, a similar change in frequency takes place: the wavelengths of light rays increase, that is move toward the red end of the spectrum, when the sources recedes from the observer; and wavelengths decrease, that is, shift toward the blue end of the spectrum, when the light source approaches the observer.

Our Modern Picture of the Universe cont.
• Today scientists describe the universe in terms of two basic partial theories- the general theory of relativity and quantum mechanics. They are the great intellectual achievements of the 20th Century. • General relativity predicts there to be a point in time at which temperature, density and curvature of the universe are all infinite, a situation mathematician call a singularity. To a physicist this means that Einstein’s theory breaks down at that point and therefore cannot be used to predict how the universe began, only how it evolved afterwards. • The term “big bang” was coined in 1949 by Cambridge astrophysicist  Fred Hoyle. The first direct observations supporting the idea did not come until 1965, with the discovery that there is a faint background of microwaves throughout space. This Cosmic Microwave Background radiation or CMBR is radiation left over from the very hot and dense early universe that would have existed shortly after the big bang.

The Sun and the Stars • What is the Sun really? • The Chinese tell of a time when our cosmic environment suddenly changed. Ten suns appeared in the sky. The people on earth suffered greatly from the heat, so the emperor ordered a famous archer to shoot down the extra suns. The archer was rewarded with a pill that had the power to make him immortal, but his wife stole it. For that offence she was banished to the moon. • The Chinese were right to think that a solar system with ten suns is not friendly to human life. Any solar system with multiple suns would probably never allow life to develop. • The sun is a star. It is no different from lots of other stars, except that we happen to be near it so it looks much bigger and brighter than the others. It is not just a little bit nearer than any other star; it is vastly nearer. • The distance between each star and its planets is usually small compared to the distance between the stars themselves.  

How stars work?
• The difference between a star (like the sun) and a planet (like Mars or Jupiter) is that stars are bright and hot and we see them by their own light only, whereas planets are relatively cold and we see them only by reflected light from a near by star, which they are orbiting. • The larger any object is, the stronger the gravitational pull towards its centre. Everything pulls everything by gravity. • A star is much larger than a planet like Earth, so its gravitational pull is much stronger. The middle of a large star is under huge pressure because a gigantic gravitational force is pulling all the stuff in the star towards the centre. And the greater the pressure inside a star, the hotter it gets. • When the temperature gets really high the star starts to behave like a sort of slow-acting hydrogen bomb, giving out huge quantities of heat and light, and we see it shining brightly in the night sky. • The intense heat tends to make the star swell up like a balloon, but at the same time gravity pulls it back again.

• There is a balance between the outward push of the heat and the inward pull of gravity. The star acts as its own thermostat. The hotter it gets, the more it swells, and the bigger it gets, the less concentrated the mass of matter in the centre becomes, so it cools down a bit. This means it starts to shrink again, and that heats it up again and so on. • There are lots of different kinds of stars. Our sun is not very big, as stars go. It is slightly bigger than Proxima Centauri, but much smaller than lots of other stars. • The most recently discovered stars like Eta Carinae and RI36a1 are 100 times as massive as our sun, or even more. And the sun is more than 300,000 times the mass of the Earth, which means that the mass of Eta Carinae is 30 million times that of the Earth. • If a giant star like R136a1 has planets, they must be very very far away from it, or they would be instantly burned to vapour. Its gravity is so huge (because of its vast mass) that its planets could indeed be a very long away and still be held in orbit around it.

The life story of a star
• Actually, it is unlikely that there are any planets orbiting R136a1, let alone any life on them. The reason is that extremely large stars have a very short life. R136a1 is probably only about a million years old, which is less than a thousandth of the age of the sun so far: not enough time for life to evolve. • The sun is smaller, more mainstream star, the kind of star that has a life story lasting billions of years (not just millions), during which it proceeds through a series of stages, rather like a child growing up, becoming an adult, passing through middle age, eventually getting old and dying. • Mainstream stars mostly consist of hydrogen, the simplest of all the elements. The slow-acting hydrogen bomb, in the interior of a star coverts hydrogen to helium, the second simplest element, releasing a massive amount of energy in the form of heat, light and other kinds of radiation. • The size of a star is a balance between the outward push of heat and the inward pull of gravity. This balance stays roughly the same, keeping the star simmering away for several billions of years, until it starts to run out of fuel. What usually happens then is that the star collapses into itself under the influence of gravity- at which point all hell breaks loose. 

• The life story of star is too long for astronomers to see more than a tiny snapshot of it. Astronomers can find a range of stars, each at a different stage of its development: • some “infant” stars caught in the act of being formed from clouds of gas and dust, as our sun was four and a half billion years ago; • Plenty of “middle-age” stars like our sun; • And some old and dying stars. An ordinary star like our sun eventually runs out of hydrogen and starts burning helium instead. At this stage it is called a “red giant”. The sun will become a red giant in about five billion years’ time, which means it pretty much in the middle of its life cycle at the moment. Long before then, our poor little planet will have become much hot to live on. • In two billion years the sun will be 15% brighter than it is now, which means the Earth will be like Venus is today. No body could live on Venus because its temperature is over 400 degrees Celsius. But two billion years is a long time and humans will almost certainly be extinct long before then, so ther will be no body left to fry. 

POWERPOINT 2
Title: Formation of Solar System and the Start of Life
Looking for exploding stars 
• For many years astronomers are looking for exploding stars. Using the most advanced telescopes, they have been collecting electronic images of distant galaxies at a time. The astronomers are looking for exploding stars within these very distant galaxies. An explosion appears as a relatively bright spot of light on the photograph of the galaxy. • Sometimes, when a very massive star collapses, the outer regions of the star may get blown off in a tremendous explosion called a supernova. • The word nova means new, and a nova- a sudden brightening of an invisible star was thought to be a birth of new star. A supernova explosion is so huge that it can give off more light than all the other stars in its galaxy combined. Ironically, it signifies the death of a star, rather than its birth. • One example of this is the supernova whose remnants we see as the Crab Nebula. The Chinese recorded it. In AD 1054, Chinese astronomers recorded a «guest star» that had appeared suddenly in the vicinity of the star we know today as as Zeta Tauri. Within a month, the star disappeared, but a nebula remained (giant cloud of gas and dust) visible today with a medium-power telescope.

Type II Supernova
• In 1987, a supernova was observed in the Southern hemisphere by modern-day stronomers and the wealth of results from their research has taught us much about these mysterious explosions in the night sky. The 1987 explosion was the first that could be seen with the naked eye. •  When a massive star- much more massive than the sun- is through converting its hydrogen into helium and helium into carbon and the later nuclear reactions that make it burn as a bright a star have all been exhausted, the star can no longer hold itself up against gravitational collapse. As it falls inward under its own weight, the star explodes spectacularly. This explosion is called a Type II Supernova. Then , depending on its size, the star’s remnants will turn into a dense dead body called a neutron star (in which ordinary protons and electrons can no longer coexist and they fuse together to form neutrons), or in the more massive cases- a black hole, the most bizarre object in the universe. • In this latter case (black hole), the object is so dense and its gravitational pull so immense that even light cannot escape it.

Type Ia Supernova • A Type Ia supernova occurs after a white dwarf , the dead remains of a star of the same type as our sun (which will, itself, become a white dwarf when it is through with its own nuclear fuels in another five billion years), begins to collect matter that falls into it from a nearby companion star, each star orbiting the other. Once the incoming matter inflates the mass of the white dwarf to about 1.4 times the mass of our Sun, a sudden explosion of unequalled violence occurs. • The brightness of the Type Ia supernova makes it almost as luminous as an entire galaxy. The explosion is immense and clearly identifiable by its characteristics. • And because of the later property, finding such supernovae has become an urgent goal for all astronomers interested in measuring the distance and speed of recession of far away galaxies.

Are we stardust?
• What if Eta Carinae were to explode as a supernova tomorrow? That would be the mother of all explosions. But do not worry: We would not know about it for another 8,000 years, which is how long it takes light to travel the vast distance between Eta Carinae and the Earth (nothing travels faster than light). What, then, if Eta Carinae exploded 8,000 years ago? Well, in that case the light and other radiation from the explosion really could reach us any day now. The moment we see it, we will know that Eta Carinae blew up 8,000 years ago. • Only about 20 supernovas have been seen in recorded history. • Supernovas, unlike ordinary stars, can create elements even heavier than iron, lead, and uranium, for example. The titanic explosion of a supernova scatters all the elements that the star, and then the supernova have made, including the elements necessary for life, far and wide through space. That is where the matter in our planet came from, and that is why our planet contains the elements that are needed to make us, the Carbon, Oxygen, and Nitrogen and so on. They come from the dust that remained after a long-gone supernova lit up the cosmos. The Nebular Hypothesis • The earth is one of a number of bodies called planets, which revolve about a central heated body, the Sun. The planets, with their attendant moons or satellites and a number of smaller bodies revolving around the sun in the same direction and nearly in the same plane, constitute our solar system. • The nebular hypothesis is a theory which involves the suggestion of a common origin for all members of the solar system from a mass of heated gaseous material (Latin. Nebula, cloud) in motion, which is supposed to have occupied all the space between the central sun and the orbit of the outermost planet. • In the process of cooling and condensation rings of matter were formed, which later broke up into different planets. • The earliest period of the earth’s geological history is termed the Archaean Era. At first all the substances, including the water which now covers three quarters of the earth’s surface, were held suspended in the atmosphere, owing to the high temperature. Later there came a time when the waters condensed and the surface, cooled still further, permitted the water to cover the rocks of the early crust entirely or in part. • Volcanic upheavals must have been frequent as fire and water struggled for the mastery. During this time of course, no life was possible.

WORD DOC
Hypotheses about the origins of life
Introduction
      If there were other life out there in the universe, how similar do you think it would be to life on Earth? Would it use DNA as its genetic material like you or me? Would it even be made up of cells?
      We can only speculate about these questions, since we have not yet found any life forms from off the Earth. But we can think in a more informed way about whether life might exist on other planets, and under what conditions, by considering how life may have arisen right here on our own planet.
      In this lecture, we will examine scientific ideas about the origin of life on Earth. The when of lifes origin (3.53.53, point, 5 billion year ago or more) is well supported by fossils and radiometric dating. But the how is much less understood. Hypotheses about the origin of life are much more hypothetical. No one is sure which hypothesis is correct- or if the correct hypothesis is still out there, waiting to be discovered.
      The earliest evidence of life on Earth comes from fossils discovered in Western Australia that date back to about 3.53.53 point, 5 billion years ago.

How might life have arisen?
       In 1920s, Russian scientist Aleksander Oparin and English scientist Haldane both separately proposed what is now called the Oparin-Haldane hypothesis: that life on Earth could have arisen step by step from non-living matter through a process of gradual chemical evolution.
       Oparin and Haldane thought that simple inorganic molecules could have reacted with energy from lightning or the Sun, to form building blocks like amino acids and nucleotides, which could have accumulated in the oceans, making a primordial soap.
       The building blocks could have combined in further reactions, forming larger, more complex molecules (polymers) like proteins and nucleic acids.
The polymers could have assembled into units or structures that were capable of sustaining and replicating themselves. The basic idea- spontaneous formation of simple, then more complex, then self-sustaining biological molecules or assemblies. From inorganic compounds to building blocks.
The Miller-Urey Experiment
     In 1953, Stanly Miller and Harlold Urey did an experiment to test Oparin and Haldanes ideas. They found that organic molecules could be spontaneously produced under reducing conditions thought to resemble those of early Earth.
     Miller and Urey built a close system containing a heated pool of water and a mixture of gases that were thought to be abundant in the atmosphere of early universe, such as water, methane, hydrogen and ammonia. To stimulate the lightning that might have provided energy for chemical reactions in Earths early atmosphere, Miller and Urey sent sparks of electricity through their experimental system.
     After letting the experiment run for a week, Miller and Urey found that various types of amino acids, sugar and other organic molecules had formed. Large, complex molecules like DNA and protein were missing, but the Miller-Urey experiment showed that at least some of
the building blocks for these molecules could form spontaneously from simple compounds.
A variety of experiments done have shown that organic building blocks (especially amino acids, can form from inorganic precursors under a fairly wide range of conditions. It seems reasonable to imagine that at least some of lifes building blocks could have formed abiotically on early Earth. However, exactly how and under what conditions, remains an open question.
From building blocks to polymers
     How could monomers (building blocks) like amino acids or nucleotides have assembled into polymers, or actual biological macromolecules on early Earth? In cells, polymers are put together by enzymes. Monomers may have been able to spontaneously form polymers under the conditions found on early Earth.
     How the polymers would have become self-replicating or self-perpetuating, meeting the criteria for life.
The “genes-first” hypothesis
     One possibility is that the first life forms were self-replicating nucleic acids such as RNA or DNA. This is called genes-first hypothesis
The Metabolism first hypothesis
     An alternative to the genes-first hypothesis is the metabolism-first hypothesis, which suggests that self-sustaining networks of metabolic reactions may have been the first simple life (predating nucleic acids).
     Another possibility: Organic molecules from outer space
Organic molecules might have travelled to Earth on meteorites. Scientists have found that organic molecules can be produced from simple chemical precursors present in space.
     One meteorite that fell in 2000 in Canada contained tiny organic structures dubbed organic globules. Nasa scientists think this type of meteorite might have fallen to Earth often during the planets early history, seeding it with organic compounds.