The origin of the Universe is unknown -- it is the ultimate mystery of this whole story. The laws of physics which applied in the beginning are not clear, so it is hard to guess where it might have come from. There are several theories of how the Universe began. This web site follows the inflationary theory of creation, which seems the most plausible.
We use the word Macrocosmos to mean "everything there is". We will see that the Cosmos and the Universe are just small parts of the Macrocosmos. So how could it have begun?
Perhaps it was created out of nothing. To us, used to the idea that energy cannot be created, this seems impossible, but even today we find two kinds of matter (matter and antimatter) being created together out of nothing in quantum fluctuations. What is more, gravitational energy is equal and opposite to the matter energy in a closed space. This means that starting from nothing gravity and matter might have separated to create the Macrocosmos.
The amounts of energy in the Macrocosmos were small. The inflation theory predicts the Universe began with only 25g of matter! However this matter was crammed into a very very tiny space, creating an extremely high energy density.
About 300 thousand years after the Big Bang, the Universe had cooled enough for electrons to be captured by protons and alpha particlesto form atoms.
An electron is pulled towards a proton because their opposite electric charges attract each other. They stick together to form a totally new kind of object called an atom of hydrogen. In the same way two electrons were attracted to each alpha particle, which contained two protons, and were held close to it. The atom they made is called a helium atom.
Atoms are fantastic things. Around the outside of the atom the electron forms a large thin shell. Inside the atom is empty space, except for the tiny heavy proton at the center. An atom is like a football.
The electron in an atoms is like the skin of the football. Under this skin the atom is almost empty. At the center is something a football doesn't have. Held at the center by the electric force is the tiny proton. This is called the nucleus of the atom. The young Universe was full of hot atoms, moving around and bouncing off each other. They made a gas.
Once all the electrons were atoms trapped in atoms, the fog of the Universe cleared.
A galaxy is an island of billions of stars, separated from other galaxies by a vast ocean of almost empty space. In this story we look at one particular galaxy (the Milky Way), since that is the one we know best, the one where we live. But we should not forget that, scattered far and wide across the Universe, there are billions of other galaxies, probably very similar to ours.
Galaxies are either spiral (about 70% of galaxies - similar to the Milky Way) or elliptical (about 30%). A few are other shapes. It is not clear how the different shapes arose. Spirals are probably more interesting than ellipticals, since stars are formed continuously in them. It is probably this which has allowed life to form in the spiral galaxy where we live.
After a while the stars formed in an open star clusterdrift apart, probably pulled by the attraction of passing stars. Let's focus down on one star and see how it works.
A star (such as the Sun) is a ball of gas which has, at its heart, a nuclear fusion reactor. It is important to know something about how stars work, for several reasons.
- One star, the Sun, is the source of almost all the energy used by living things, including humans. We could not survive without it.
- If we could copy the Sun in a small and controlled way, we believe we could obtain a great deal of energy on Earth without creating a lot of pollution.
- Stars are the places where large atoms are built. Past generations of stars formed the gas and dust from which the planets and life were made.
We have seen that a small red giant, up to 1.5 times the size of the Sun, turns into a white dwarfwhen it dies. Larger red giants, however, die in a more spectacular way.
Once the nuclear fuel is exhausted in a red giant, the core starts to cool and the internal pressure falls, leading to contraction. In large red giants this is a sudden and catastrophic event so that the star collapses. As the outer layers of the star fall they gain heat. This triggers nuclear fusion in these outer layers and they explode in a spectacular explosion called a supernova, becoming for a few days brighter than a whole galaxy.
With so much energy it is possible to fuse iron nuclei into even heavier ones such as uranium nuclei. As the star explodes it throws out the nuclei which it has made. On their way out they pick up electrons and become atoms. The helium, oxygen, carbon, nitrogen, iron, uranium and other heavy atoms made by the star are scattered back to dust in the disc of the galaxy. In this way the atoms made in one generation of stars are passed on to be used by the next.
So all the atoms in your body (except hydrogen) were made in a supernova 5 billion years or more ago.
What happens next depends on the size of the original star.
We have seen that a small red giant, up to 1.5 times the size of the Sun, turns into a white dwarfwhen it dies. Larger red giants, however, die in a more spectacular way.
Once the nuclear fuel is exhausted in a red giant, the core starts to cool and the internal pressure falls, leading to contraction. In large red giants this is a sudden and catastrophic event so that the star collapses. As the outer layers of the star fall they gain heat. This triggers nuclear fusion in these outer layers and they explode in a spectacular explosion called a supernova, becoming for a few days brighter than a whole galaxy.
With so much energy it is possible to fuse iron nuclei into even heavier ones such as uranium nuclei. As the star explodes it throws out the nuclei which it has made. On their way out they pick up electrons and become atoms. The helium, oxygen, carbon, nitrogen, iron, uranium and other heavy atoms made by the star are scattered back to dust in the disc of the galaxy. In this way the atoms made in one generation of stars are passed on to be used by the next.
So all the atoms in your body (except hydrogen) were made in a supernova 5 billion years or more ago.
What happens next depends on the size of the original star.
Planets are lumps of gas and rock held close to a star by the force of gravity. We live on planet Earth going round star Sun, along with eight other planets. Together these are called the solar system.
Because stars form in dark clouds of dust and molecules in open star clusters, it is difficult to watch them form. So the story of how planets formed which we have just given has not been confirmed by observation.
About 20 planets have been discovered near Sun-like stars, although they are hard to see. Looking for planets near a star is a bit like trying to watch a moth flying around a spotlight which is pointing at you -- you get dazzled by the light. See the article Giant Planets Orbiting Faraway Stars for an explanation of how they are found.
Since discs of gas and dust have been detected around some young stars, we guess that planets might be common. But none of the planets so far discovered are like our Solar System. Indeed these discoveries are challenging current theories of the origin of planets.
If planets like ours are common, then life too could be common in the Galaxy.
We will now focus down on one tiny planet: the Earth. Notice from our diagram and model of the solar system how small it is compared to the Sun and the giant planets Jupiter and Saturn. If we didn't live here we probably wouldn't even notice it!
Yet there is a very good reason why we should look at this planet and no other. The Earth is the only planet on which water forms a liquid, which is essential for life. The reason has to do with its distance from the Sun. A planet further from the Sun, like Mars, is so cold that water freezes into ice. Closer to the Sun, like Venus, water boils and all the molecules fly apart. Only on the Earth can water form that marvelous substance, liquid water. The Earth, like most of the other planets in the Solar System, has an almost perfectly circular orbit. This is unusual. In most of the other planetary systems studied the planets have oval (elliptical) orbits. If the Earth had an oval orbit, travelling sometimes near to the Sun and sometimes far from it, life could not have evolved on the planet. At times the oceans would have boiled and at times they would have frozen, and life as we know it would have been difficult if not impossible.
Because they were made from a spinning disc, all planets spin like tops and they orbit (go round) the Sun. The Earth spins once a day and orbits once a year. The points which the Earth spins round are called the north and south poles.
Earth is the third planet from the Sun.
Life is a chemical system involving two types of molecules, proteins and nucleic acids, working together in a very special way. First we will look at these two types of molecule in turn. Next we will look at how they work together to make life. Then, when we know a little about what life is, we will think about how this beautiful chemistry might have started.
The first cellsappeared on Earth about 3.5 billion years ago. These early cells were very similar to the simplest cells we find on Earth today, called bacteria (sometimes called germs). Note that one of these is called a bacterium. Later bacteria evolved many new features. For example bacteria could swim. They used a long twisted whip-like tail called a flagellum fixed to a wonderful tiny rotating motor. This made the flagellum twist round and so pushed or pulled the bacterium along!
Bacteria have only one cell each. They can be round (coccus), rodlike (bacillus), or curved (vibrio, spirillum, or spirochete). Bacteria live almost everywhere on Earth, including the soil, water, organic matter, and the bodies of multicellular animals (eukaryotes). Some bacteria benefit humans and other plants and animals. Others are harmful; bacteria are the chief cause of infectious diseases in humans.
Bacteria differ from more advanced cells such of those found in animals and plants because they have no membrane around their nucleus nor any organelles. Simple cells like this are called prokaryotes. Bacteria make up the group which biologists call monera.
Archaebacteria are probably living fossils, similar to the earliest bacteria.
At some stage in history a process called continental drift began. We do not know when because the rocks have been squashed and changed so much since then, but it is important because it is still happening today. Some people think that it is one cause of ice ages.t is the heat generated by radioactive decay inside the Earth which drives this process. Today the theory of plate tectonics, which includes continental drift, forms a framework for the study of geology and the earth. Hot rock rises up from the mantle and spreads out on the surface to form the ocean floor. As the ocean floor spreads it pushes the continents around. They move one or two centimeters each year. As the continents move around they sometimes hit each other, creating mountains. This is how the Alps and the Himalayas were created. Mountains like this are on the inside of continents. Sometimes continents do not hit head on, but rub past each other. Since they do not have smooth edges, the rubbing is jerky and uneven. Pressure builds up and is then suddenly released. This creates earthquakes. The San Andreas fault in California is an example of this. n some places the floor sinks back down into the mantle, usually at the edge of a continent. As it sinks it melts and hot rock rises up, creating volcanoes along the coast. The Andes are being created in this way. Sometimes the volcanoes lie in an arc just off the coast of a continent. The islands of Japan are being formed like this.
t seems that the evolution of all successful animals began with ancestors similar to modern flatworms. Around 570 million years ago more advanced animals appeared.
Three types of animals were so successful that they are still the commonest animals today. All three types had hard outer coverings on their bodies. We call them
- Molluscs
- Arthropods
- Vertebrates
The molluscs and arthropods belong to a group of animals called the protostomia, while the vertebrates are deuterostomia.
he animals we lump together as fish actually consist of several very different groups of vertebrates:
- Jawless fish
- Bony fish
- sharks
- ray finned fish
- lobe finned fish
Once the plants and arthropods were living on land there was plenty of food for any vertebratewhich could manage to come out of the water. Some fish lived in ponds which dried up in summer. Their swim bladders evolved into lungs which they used to breathe air. They used their fins to crawl from one pond to another and these evolved into legs, two at the front and two at the back.
The vertebrates which emerged from the water and became land animals around 350 million years ago we call amphibians "am-fib-ee-ans". Their name means "both lives" because they lived both in water and on land at different times in their lives.
Leaving the water was one of the greatest steps ever taken by our ancestors. It needed changes in every part of the body. The most obvious changes were the appearance of legs and the ability to breathe. Other changes were not so obvious but were just as important. For example the way the blood flowed round the body had to change.
Amphibians were still not totally free from the water. They needed to return to it to reproduce (like the ferns and the arthropods before them). Their eggs were laid and fertilized in water and the young developed in the water just like their fishancestors. But when amphibians grew up they left the water to live on the land. Most frogs and newts are still at this stage of evolution. By 350 million years ago ferns the size of trees were common. They had solved most of the problems of living on land but were still tied to moist ground for their reproduction. Many ferns grew in swamps. They grew from a small underground growth called a prothallus. The sperm swam from one prothallus to fertilize the egg on another. Without water or wet ground they could not reproduce.
When they died some ferns fell into the swamp. Decomposition could not happen because there was no oxygen in this water so the plants were buried and eventually turned into the stone we call coal.
The ferns we see today are still among the most primitive of plants. Their fronds uncurl and carry spores on their undersides.
Soon a group of vertebrates called reptiles solved the problem of how to reproduce without water, and they did it in exactly the same way, as the insects. Fertilizationoccurred before the eggs were laid, by the male injecting sperm into the female's body.
She used it to fertilize her eggs which she then covered with a tough water-proof skin and laid on land. No surface water was needed for reproduction.
Reptiles had scaly skin. They probably could not keep themselves warm when the weather was cold or at night-time, and may have become slow and sleepy at these times, although there is some debate about this.
Plant seeds could not grow or spread very quickly. They needed the wind to carry the pollen to the egg. Also it took over a year for the plant to store enough food in the seed to make sure the baby plant could grow.
About 200 million years ago a new kind of plant evolved. It attracted insects using colored flowers, and gave them sugary nectar to eat. Bees, butterflies and other animals evolved to eat the nectar offered by the flowers. While eating they picked up pollen on their bodies which they carried to other flowers.
The pollen itself was different. It carried two sperm. One fertilized the egg. The second fertilized the flower which then grew rapidly into a fruit. The seed used this for food. These flowering plants could grow and make fruits in just a few weeks, so they spread much faster than the seed plants. Fruits, berries and nuts appeared, so there was lots of new food for animals. New animals evolved to eat the fruit. The land became filled with the color and scent of many beautiful blooms. The hardwood trees and other plants of the tropical rain forest, now being so rapidly destroyed by people, are of this kind.
Improvements in reproduction were happening in the vertebrate world too. Instead of laying their eggs, female mammals kept them inside their bodies while they developed. In this way they protected their young, feeding them and giving them oxygen. The young could develop larger brains and more advanced bodies than any reptile.
After birth the young were looked after by their mothers, who fed them a rich food called milk. Mammals were the only animals able to make this wonderful food. Then began a long period of care and training when the young learnt from their parents.
Unlike dinosaurs, who probably needed the Sun's heat to keep them warm, the mammals had fur to keep them warm. They also had a better blood system.
Mammals were also far more intelligent than dinosaurs. Even the stupidest mammal is a genius compared to the brightest reptile. Their long development, when they are cared for by their mother, is what lets mammals' brains grow so much more than reptiles'.
Mammals first appeared about 200 million years ago. It is strange that while the mammals had better bodies and brains than the dinosaurs, even so for a long time they were unable to spread. This was probably because most life-styles were already taken by the less advanced but more common dinosaurs. Mammals stayed as small shrew-like insect-eating animals, perhaps only coming out at night.
Some people find it hard to accept that humans have evolved from animals. Yet there are many facts leading to that idea. Human cells are eukaryotic, the same as animal cells. Our chromosomes and genes are almost identical to some of the apes. So are our tissues and organs. Fossil bones have been found, showing how people evolved.
The main difference between people and other animals is their ability to think, which comes from the large size of their brain, and their use of language.
Modern people (Homo Sapiens) seem to have evolved in Africa about 100 thousand years ago (although the date is far from clear) and lived there while the Neanderthals were spreading around the world.
An interglacial (warm period) began 35 thousand years ago. Then modern people came out of Africa and spread. Within a few thousand years they replaced the Neanderthals in Europe and Asia. Then about 25 thousand years ago the weather turned cold again and a glacial began. During the glacial, people improved the tools used by Neanderthals, developing specialized tools for different jobs.
But the thing which really set them apart from Neanderthals was their use of art and decoration. Cave paintings, beads, clay statuettes, carvings on the handles of tools, all show a more developed sense of art than Neanderthals ever did.
Many animals were hunted to extinction and people spread around the world.
The weather turned warm 11 thousand years ago and the present interglacial began. Many of the glaciers melted, it rained heavily, and the oceans rose 100 meters. New animals and plants replaced the old. People took up two different ways of life: Nomads and farmers.
Computers are now being invented and have already
left the Earth and begun to explore the solar system.
They will soon begin to design themselves,
and so become independent of their human inventors.
There are vast resources in space and huge amounts of energy,
so computers will rapidly colonise this corner of the Galaxy.
The Sun will eventually burn up the Earth,
but by that time organic life will be largely irrelevant.
The Universe will probably end by cooling and expanding to almost empty space.
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