The following timelines attempt to show key events leading to modern humans from the very beginning. The emphasis is on developments which were beneficial to our appearance and survival on Earth and might be shown one day to have parallels to those on exoplanets with exobeings. N.B.: The dates given are approximate.
History of the Universe and Our Solar System
| Years in past | Events |
| 13.8 bya | Sudden, enormous expansion, known colloquially as the Big Bang, from an infinitely dense and hot origin. Time and space comes into existence. 380,000 years later the universe has cooled enough for atoms to form, mostly hydrogen with some helium. |
| 13.6–13.5 bya | Vast clouds of gas and dust show slightly irregular distributions due to quantum fluctuations at the very beginning, which are exaggerated during a period of exponential inflation (during a tiny fraction of first second after the ‘bang’). The collapse of these clouds leads to the first galaxies, including the Milky Way, which probably later absorbed other galaxies with which it collided. It is one of about 100,000 galaxies in the Laniakea Supercluster (this also subsumes the Virgo Supercluster, see Figure 4.2). |
| 5 bya | Our Solar System – the Sun, planets and asteroids – evolves from a huge disk of dust and gas (nebula), which had developed clumps and increased due to gravitational attraction (similar nebulae can still be observed within our galaxy). Nuclear fusion begins in the centre of the Sun, leading to it emitting light and heat. Our Sun is a third-generation star, which evolved from the gas and debris of previous stars that already contained heavy elements. |
| Our Solar System is located in the Orion–Cygnus arm far away from the centre of our galaxy (over 26,000 light years).The Earth develops a magnetic field due to its outer core of molten iron continually moving and thus produces a dynamo effect. The magnetic field shields the Earth from harmful radiation from the Sun (solar wind) and from space (cosmic rays). | |
| 4.5 bya | The Moon forms due to the collision of the Earth with a planetary body (called Theia) about the size of Mars; this hurls huge quantities of material into space, which ends up orbiting Earth and clumping to form the Moon. Because of its size, about a quarter of the diameter of the Earth, and its position (about 384,000 kilometres from the Earth), the Moon has a stabilising effect on the rotation of the Earth. |
History of Our Earth
| Years in past | Events |
| 4.55 bya | The Earth forms from rocks orbiting fairly near the Sun (like Mercury, Venus and Mars), which stuck together, exerting a gravitational pull that led to them accruing more material. The gas and ice giants (Jupiter, Saturn; Uranus and Neptune) develop and maybe migrate to their present positions. Planets also have moons which arise from local concentrations of material. In some cases, large amounts of water (already existent in the universe) are added to planets and moons and captured in comets, which orbit the Sun along long irregular pathways. |
| 4 bya | After the period of Late Heavy Bombardment, the Earth is free of serious impacts from space. Prokaryotes (simple cell microorganisms) arise. The Earth is anaerobic (lacking oxygen) to begin with but this changes when vast quantities of cyanobacteria release substantial amounts of oxygen into the atmosphere. |
| 2.5–2 bya | The first eukaryotes arise through the incorporation of one type of prokaryote into another. The resulting complex cells still have mitochondria, stemming from the incorporated prokaryotes with their own, now inactive DNA providing evidence of this process. Cells develop membraned nuclei and various organelles, different functional parts within a cell. Complex life forms begin to arise. Early forms might have developed near hydrothermal vents (such as black smokers) on the ocean floor. |
| 1.2–1 bya | Sexual reproduction appears. Instead of simple cell divisions with identical results (mitosis), a system of meiosis develops. Here cells resulting from division (one to two to four) only contain half the chromosomes of the first cell. These cells are called gametes, two of which fuse together during fertilisation. As gametes come from different sources, one from each parent, a genetic mixture occurs which is typical of all sexually reproducing eukaryotes and ultimately of humans, where the large gamete is the egg of the mother and the smaller gamete is the sperm of the father. |
| 1 bya | Forms of life evolve with a bone structure running through the centre of the body (vertebrates). These have a brain-like structure at one end where the mouth (for food intake) and major sensory organs are located. At the other end is an anus permitting waste to pass from the body. The brain controls the nervous system, which extends down the back (spinal cord) and branches out into the various limbs. |
| 540 mya | Cambrian ‘explosion’: a sudden increase in life forms, with skeletons and hard bodies (shells), is apparent in the fossil record. Several unique life forms date to this period, above all those involving predation. |
| 370 mya | Life forms move from the sea to the land. The source of these are lobe-finned fish, which had leg-like, jointed fins and primitive lungs. The latter probably developed to cope in aquatic situations with low oxygen, such as in shallow swamps. These fish are the ancestors of all tetrapods – four-limbed creatures. (Sea mammals resulted from a re-migration from land to the sea about 50 mya.) |
| 252 mya | Permian–Triassic extinction event, known as the Great Dying, leads to the extinction of over 80 per cent of all marine life and about 70 per cent of all terrestrial life. This is the most severe of all extinction events; its cause is uncertain, but asteroid impact, supervolcanoes, sudden depletion of oxygen in the air and sea have all been put forward as possible reasons. |
| 240 mya | The age of the dinosaurs begins. They come to dominate animal life across Earth. |
| 66 mya | A major asteroid impact occurs near the Yucatán peninsula (present-day Mexico). The resulting ecological catastrophe (fires, tsunamis, blocking of sunlight for decades) eradicated the dinosaurs and nearly all other forms of life. Some animals survive, like reptiles and birds. The demise of the dinosaurs opens the way for other vertebrates, above all mammals, to evolve unhindered. |
History of Homo Lineages
| Years in past | Events |
| 10 mya | Earliest apes evolve. Somewhat later gorillas and chimpanzees split. |
| 6–7 mya | The tribe hominini split with the last common ancestor between chimpanzees and the genus Australopithecus ‘southern ape’ (precursors of Homo species). |
| 4–1.5 mya | Habitual bipedality develops early on. Primitive tool making appears with Homo habilis (c 2.4–1.6 mya). Homo erectus (c. 2–0.12 mya) is the next major species which spreads throughout Africa and Eurasia even reaching east Asia as the remains of Homo floresiensis in Indonesia probably show. By about 0.5 mya Homo heidelbergensis had reached Europe and Homo naledi is documented for South Africa by about 0.3 mya. By about 60 kya Oceania and Australasia are settled by anatomically modern humans. |
| 1.5–1 mya | Management of fire achieved, affording protection from predators and furthering social bonding. Cooking of food follows shortly afterwards, greatly improving energy intake in a short period of time. This is taken as furthering brain volume with an attendant reduction in gut size. The reduction in the size of the teeth (especially the molars) and the jaw muscles may be related to the increasing size of the brain case. |
| 600–300 kya | First modern human beings (Homo sapiens) evolve in eastern and/or southern Africa. An exact dating of their appearance is not possible. |
| 100–70 kya | Human languages among Homo sapiens have gained modern structure. This must have happened before the last dispersal, as the internal organisation of all human languages is the same today and so must derive from a common source (parallel independent development extremely unlikely). |
| 70 kya | Last wave of dispersal of Homo sapiens out of Africa via the southern Arabian peninsula up into the Near East and on to Europe also across to South, East and South-East Asia. There was a limited amount of interbreeding with the following groups. |
| 35–40 kya | Neanderthals (Homo neanderthalensis), who had emerged in Europe and Western Asia about the same time as Homo sapiens, become extinct as do other poorly documented species such as the Denisovans (central Asia). This leaves Homo sapiens as the only extant human species. |
Human History
| Years in past | Events |
| 17 kya | Wall paintings were made in a cave complex at Lascaux (Dordogne, France) which are early examples of Homo sapiens art. |
| 15 kya | Homo sapiens groups cross from Siberia through Beringia not later than 15 kya (probably earlier) and quickly spread down into North and South America. |
| 12–11 kya | Göbekli Tepe, an archaeological site in Anatolia, Turkey, is early evidence of permanent settlement and buildings.Flourishing of Fertile Crescent – modern Iraq, southern Turkey and the Levant (present-day Syria, Lebanon, Israel). |
| 11.7 kya | End of the last glacial period of the Quaternary period. Ice sheet recedes exposing the European land mass. Rise of agriculture with the domestication of plants and animals and gradual transition from hunter–gatherer groups to sedentary farming communities. |
| 11–7 kya | Beginning of Neolithic period characterised by stone artefacts and implements found in archaeological sites. |
| 10 kya (i.e. 8000 BCE) | Beginning of Yellow River (Huanghe) civilisation in China. |
| 5000–4000 BCE | Indo-European groups, living in the steppe region north of the Caucasus, begin to disperse. The dialects of these groups gradually become branches of the later Indo-European family, which still later diversify into the individual languages of groups such as Indo-Aryan, Hittite, Tocharian, Hellenic (Greek), Italic (later Romance), Celtic, Germanic, Slavic, Baltic, most of which are attested to this day (but not Hittite or Tocharian). |
| 3500 BCE | Cuneiform script was developed in the Near East and used first for Sumerian, spoken in Mesopotamia (present-day Iraq), and for the unrelated languages Akkadian and Hittite (c 3.7 kya). |
| 3300 BCE | Beginning of Indus Valley civilisation. |
| 3000–1000 BCE | Bronze Age, a designation for a period during which an alloy of copper and tin was widely used and traded throughout Europe and the Near East. |
| 1200–500 BCE | Iron Age, initiated by the so-called Late Bronze Age collapse in the Eastern Mediterranean and the Near East (including the Nile valley), during which widespread incursions and invasions disrupted communities in this large area. |
| 1000 BCE | The Phoenicians employed an alphabetic script (from an earlier form called Proto-Sinaitic); this was later adopted by the Greeks, which provided the impetus for later modern alphabets in Europe. In alphabets, letters stand for sounds, not for objects. |
| 800 BCE | Classical antiquity begins with the rise of Greek city states. |
| 500 BCE | Roman Republic is founded, continued as the Roman Empire from 27 BCE onwards. |
| 400 BCE | Detailed records of astronomy observations begin to appear in China. |
| 200 BCE | Paper invented in China. |
| 100 BCE | Antikythera mechanism constructed in Greece. |
| O CE | Beginning of the Common Era (references from here on are to centuries). |
| 3–9 CE | Classical Period of Mayan civilisation. |
| 4 CE | The Roman Empire disintegrates into an Eastern and a Western half (395 CE). The Western Roman Empire continues to decline. |
| 5–6 CE | Flourishing of Indian astronomy, which later influenced Chinese and Islamic astronomy. |
| 5–15 CE | The Middle Ages in Europe follow, a period in which theology dominates most spheres of scientific investigation. |
| late 7 CE | Printing is invented in China. |
| 8–13 CE | Islamic Golden Age, during which science flourishes. |
| 14–15 CE | Aztec civilisation flourishes in areas of present-day Mexico. |
| 14–16 CE | Inca civilisation flourishes in areas of present-day Peru. |
| 14–17 CE | The Renaissance, a period of renewed interest in classical antiquity and of scientific activity, begins in Italy and spreads to all of Western Europe. |
| 1610 | Galileo builds the first telescope and discovers the larger moons of Jupiter. |
| 1687 | Isaac Newton publishes his Philosophiæ Naturalis Principia Mathematica, laying down the foundations of classical (deterministic) physics. |
| 1799 | Alessandro Volta develops the first battery (voltaic pile), thus harnessing electricity. |
| 1831 | Michael Faraday discovers electromagnetic induction and how to use it to generate electricity. |
| 1865 | James Clerk-Maxwell succeeds in unifying electricity and magnetism in a theory of electromagnetism. |
| 1900 | Max Planck introduces the notion of quantum, the smallest packet of energy, which is later empirically attested and forms the basis for quantum mechanics. |
| 1905/1916 | Albert Einstein publishes his theory of special and general relativity, respectively, showing that the speed of light was an absolute constant, that matter and energy were equivalent and that gravity was manifested as the curvature of space–time, an assumption empirically demonstrated some years later. |
Abbreviations: bya = billion years ago; mya = million years ago; kya = thousand years ago; BCE before the common era; CE common era (references here are in centuries).
