In the Beginning... According to current scientific thinking, the age of the universe is something between 10 and 20 billion years. The age of 15 billion years we assume here, is a parametrized value (Hubble's constant, Lambda, Omega, S), implying that the least variation in the value of one "constant" will result in a change in age. There is a possibility that with time this value will no longer be correct, or that certain theories will need to be revised. T=0 in this universe: theories based upon quantummechanics cannot make any statements about what happened between 0 and c10-43 second after the Big Bang. Theories based on general relativity cannot say anything about T=0 itself. c10-43 second (s): there is a single 'super force' that comprises the four fundamental forces of nature. Shortly afterwards they split up: first gravitation, then the strong nuclear force (theories describing the unification of the three remaining forces are known as GUTs or Grand Unified Theories), finally the electromagnetic force and weak nuclear force. The universe is expanding at the speed of light. c10-35s: the temperature is 1028 K (Kelvin, 0°C = 273.15 K). Possibly primordial black holes emerge with a radius of 10-35 m and a mass of 10-8 kg. c10-13s: the universe expands further and cools down. The temperature is now 1017 K. c10-6s: the fundamental particles known as quarks have slowed down sufficiently to combine into neutrons and protons. The temperature has gone down to 1013 K. c1s: the universe is a seething sea of all sorts of subatomic particles, mainly electrons, positrons, photons and neutrinos, and a significantly smaller amount of protons and neutrons. The temperature is 1010 K. c1-100s: when the temperature has fallen to about 109 K, it becomes too cool to produce electrons and positrons (which are the same in every aspect except in charge) from the surrounding energy fields. Most electrons and positrons disappear in mutually destructive collisions. Eventually, only one in a billion electrons will remain. Once this temperature is reached, it is cool enough to form nuclei of deuterium (one proton and one neutron), followed little later by a complex chain of reactions in which deuterium captures free neutrons and protons with the production of helium and lithium as a result. A quarter of the universe's baryonic mass is being transformed into helium nuclei, a fraction into nuclei of lithium, the rest remains as hydrogen nuclei (free protons). The electrons stay unbound. c1012s: the temperature has fallen to a few thousand K (the surface temperature of the Sun is 5780 K). The nuclei combine with electrons: atoms come into existence. The capture of electrons makes the universe transparent: the photons, forming a background radiation (then at the wavelength of visible light) can move freely. As such, matter is no longer influenced by the radiation pressure and the decoupling of matter and radiation is a fact. The universe continues to expand and cool down. Under the influence of gravity clouds of hydrogen contract and proto-galaxies are formed, out of which star systems gradually emerge: eventually the first extremely heavy stars (hypothetical) appear, exploding very quickly and changing into (common) black holes. Clouds of gas contract under their own gravity and form a flat rotating disc that condenses into one or more stars, out of which, in certain cases, planets are born. Stars initially get their energy from gravitation: the temperature and pressure at the centre of the star increase. Once the critical temperature is reached (over five million K in the core), nuclear fusion starts : out of every four hydrogen atoms one nucleus of helium is formed. In doing so, nuclear energy is [being] released that keeps the gas pressure in the star high enough to counteract the contraction that would result from its own gravity. After hydrogen fusion, stars heavier than eight times the mass of the Sun can go on to convert helium into carbon and oxygen, followed by the formation of magnesium and silicon and ultimately iron. Such stars show a so-called onion structure. At this point iron cannot be converted into still heavier elements with the production of energy. Since the internal pressure can then no longer oppose gravitation, the star's centre collapses, causing the outer layers to fall into regions of higher temperature, going through accelerated nuclear fusion. As this happens, the energy [that is being] released is gigantic: the star's core collapses, but the outer regions are blown off in space with tremendous force (supernova). The heavy elements that have been formed in this process are dispersed and caught by other clouds of gas. This explains the presence of heavy elements in our solar system, such as carbon, the basic element of life. c3.1017s: In one of these star systems, a gas cloud, enriched with heavy elements, contracts to become our solar system with one star and nine planets (counting Pluto as an actual planet). One of those planets is Earth. According to our current scientific knowledge, its age is about 4.6 billion years. c4.6 billion years ago. When gravitation brings order in the chaotic matter that remains after the formation of the Sun (the accretion disc), the Earth and the planets come into existence. Accretion in this disc produces planetesimals that, close to the Sun, consist mainly of rock, but that farther away contain compounds of the lighter elements (ice, methane). Collisions of these rocky planetesimals result in the formation of the cores of the planets. The heat generated in this process is sufficient to completely melt these young planets. In the case of the young Earth, the compounds containing heavy elements like iron and nickel 'sink' to the centre of the planet; the compounds containing lighter elements such as silicon, magnesium, and aluminium stay at the surface, which cools down and forms a crust. In the meantime, the population of planetesimals decreases, resulting in ever fewer destructive impacts. Shortly after the Earth is formed, one heavy collision flings away the Earth's crust, part of which ends up in orbit around the planet: the Moon is born. The compounds with the very lightest elements ­ hydrogen and oxygen (as water vapour), nitrogen and carbon dioxide ­ are the constituents of an early atmosphere. Condensation of water vapour forms the first oceans. Besides water (ice), the impacting planetesimals also introduce complex carbon compounds. Carbon can form versatile molecules with other elements with only a small change in energy. Many of the essential materials for life consist of such complex carbon compounds. The presence of this kind of molecules has been confirmed on Halley's comet and in meteorites. The growing atmosphere and the developing magnetosphere gradually offer more protection against the cosmic radiation that would otherwise destroy all life. Prokaryote and eukaryote phylogeny These phylogenies are based upon similarities in informational molecules, namely subunits of ribosomal RNA (rRNA; RNA = ribonucleic acid). In each tree, groups that are connected have the most similar rRNA, and the length of the lines between connections, as well as of the terminal lines, reflects relative genetic differentiation. The phylogeny for the prokaryotes was assembled in the laboratories of Karl Woese and James Lake; the tree for the eukaryotes comes largely from the work of Vincent Sogin's laboratory. Only a sample of the numerous phyla of bacteria and protoctists have so far their rRNA analyzed. Thus, these phylogenies are incomplete, and some illustrated relationships may change slightly as new phyla are analyzed and added. 4 - c3.8 billion years ago. The Sun has gained in strength. The Earth's rotation slows down whilst its companion, the Moon, has doubled its initial orbital period of ten hours. Besides the predominating nitrogen, carbon dioxide, hydrogen sulphide and methane are found in the still pinky-orange atmosphere. Few modern organisms would be able to survive in this poisonous world which, after billions of years of bacterial metabolic activity, will eventually be populated by the three primary groups of life: procaryotes (archaea and bacteria) and eukaryotes ('higher' organisms). The question of spontaneous biogenesis, whether chemical processes have brought about life out of non-life, is not in scientific doubt anymore. The discussion is about which of the many conceiveable ways may have led to the first cellular organisation. Chemical evolution: survival of the stablest structures led to the emergence of more complex molecules such as RNA and DNA. A remarkable property of these molecules is their ability to replicate, as well as their information-carrying character, allowing them to build organized structures using the process of protein synthesis. Those complexes were actually minute chemical factories surrounded by a cell membrane. The first type of cell that could reproduce was born. First type of cell = RNA + DNA + cell membrane + protein synthesis + reproduction. ————————————————————————— Written and supervised by: Prof. Dr. Gustaaf Cornelis (logician and philosopher of science), Ronny Martens (astronomer), Tim Trachet (mathematician), Prof. Dr. Jean Paul Van Bendegem (logician, mathematician and philosopher of science), Prof. Dr. Walter Verraes (biologist), —————— © 2001 Tom Schoepen, http://www.worldhistorytimeline.net