Big History Thresholds
Threshold 1 - BIG BANG
Until a few decades ago it was assumed that the universe had always been in existence, a theory known as the Steady State Universe advocated by the English physicist Fred Hoyle. However, Soviet-American theoretical physicist and cosmologist George Gamow (1904 –1968), was an early advocate of Belgian Georges Lemaître’s (1894-1966) Big Bang theory. Lemaître first claimed that the recession of nearby galaxies suggested an expanding universe, a theory soon observationally confirmed by American Edwin Hubble in the 1920s. Cosmic Background Radiation (CBR) now clearly indicates an origin of the universe at a ‘Big Bang’ about 13.7 billion years ago from an object smaller than an atom and at a temperature of trillions of degrees and which expanded into everything that is in the universe today. This was also the origin of space and time and it was assumed therefore that to ask ‘What happened before the Big Bang’ was a meaningless question.
After an initial period of inflation expansion slows and different energies emerge (gravity, electromagnetism, strong and weak forces holding atomic nuclei together) matter emerges (dark matter, and atomic matter consisting of quarks and electrons). In recent years physicists have postulated a multiverse with the Earth just one among many universes though evidence for this theory is slim.
Pre- Big Bang – Unknown. Current speculation suggests either nothing (no time or space), or a multiverse.
BB 13.8 billion years BP – an object smaller than an atom at a temperature of trillions of degrees expands giving rise to everything that is in the universe today
BB + 1 second – expansion slows and different energies emerge (gravity, electromagnetism, strong and weak forces holding atomic nuclei together) matter emerges (dark matter, and atomic matter consisting of quarks and electrons)
BB + c. 380,000 years – expansion & cooling to a temperature at which electrons and protons (ionised plasma) unite to form electrically neutral atoms with enormous release of energy as cosmic background radiation (CMB) or cosmic microwave background (CMB).
Threshold 2 - STAR FORMATION
BB + a few million years – uniform distribution of dark matter, energy, hydrogen, and helium atoms but very slight gradients in temperature. Gravity pulls matter into stars and galaxies creating sufficient heat to splits atoms which then fuse to form helium nuclei setting up a counter force to gravity. The universe now has stars and galaxies with substantial differences in temperature, density and gravitational energy.
13.8 billion years The Big Bang
3 minutes after the Big Bang – The formation of hydrogen and helium nuclei
380,000 years after the Big Bang – The release of cosmic background radiation and the formation of electrically neutral atoms of hydrogen
560 million years after the Big Bang – The first stars flare into life with galaxies forming soon after (approximately 500 million years after the Big Bang
8-10 billion years – The formation of our galaxy, the Milky Way, from the mergers of several other galaxies
4.567 billion years – Formation of the Sun and the beginning of the formation of our solar system.
Threshold 3 - ELEMENTS IN STARS
+ c. 100 million years. Universe mostly hydrogen and helium atoms but new elements are now formed. As stars had fused all its protons (burned out) to produce helium nuclei the centre collapses as gravity takes over and temperatures rise so high that helium nuclei now fuse to form carbon, nitrogen, and oxygen, proceeding through the periodic table until the centre of the star consists of iron (element 26 in the periodic table) – if big enough (and gravity therefore strong enough) a supernova explosion occurs forming all the other elements in the periodic table – over 90 elements that can combine in various ways.
Linking thresholds 1-3:
10^(-43) seconds after the Big Bang – 10 to the power of negative forty three seconds. The smallest space of time that has any physical meaning; Planck time
10^(-36) to 10^(-32) seconds after the Big Bang – Inflation, formation of the four fundamental forces of physics, quantum fluctuations create the tiny “wrinkles” in density that prevents the Universe from being totally homogenous and “stillborn”
The Next 10 seconds after the Big Bang – Quarks and anti-quarks, electrons and positrons combine and annihilate into energy, one-billion of quarks and electrons remain without a partner
The Next 3 Minutes – The Universe cools to the point that hydrogen and helium nuclei form from quarks (that formed into protons and neutrons)
380,000 Years after the Big Bang – The Universe cools to 3000K and becomes “electrically neutral”, allowing nuclei to gain electrons and form fully fledged atoms, photons able to move freely, and the release of Cosmic Background Radiation
200 million Years after the Big Bang – The formation of the first stars and galaxies from clouds of hydrogen and helium gas, followed by the death of the first stars and the creation of the remainder of the 92 naturally occurring elements on the Periodic Table.
Threshold 4 - SOLAR SYSTEM
Emergence of planets and solar systems as materials and molecules orbiting stars undergo accretion to form planets. In our solar system the rocky heavy planets form closer to the sun and the gaseous ones further away. The earth became molten and with the heaviest elements at its core, as iron, differentiated to the lightest in the mantle and on the surface as as granites and basalts and above this the gaseous atmosphere. The mantle drifts on the fluid as the continents move relative to one-another (continental drift). Amino acids are formed. The Earth is molten with an iron core, mantle and crust and, at first, no free oxygen. Planets and solar systems are chemically and structurally more complex than stars.
4.57 billion years – Gas cloud condenses, contracts, and increases rotation to form protoplanetary disk
4.5682 billion years – Oldest grains in the solar system form (calcium-aluminium inclusions, and some chrondrites)
+10 million years – Gas giants had largely formed, probably much closer to the Sun than at present
+10 million years – Solar wind clears out much of the gas disk, ending growth by gas accretion
c.4.5 billion years – Jupiter migrates inwards, preventing planet formation in the asteroid belt, and limiting the supply of material to Mars. It then enters into a resonance with Saturn, and moves to current orbit
4.45 billion years – Terrestrial planets had largely formed by continual accretion of rocky protoplanets, and formed metal cores. Moon forming impact
4.4 billion years – Oldest preserved zircon grains
4.2 billion years – Oldest rocks on Earth
3.9 billion years – A 2:1 resonance between Jupiter and Saturn causes Neptune to leap outside Uranus’s orbit, and they both migrate into the outer solar system, causing a massive disruption in the Kuiper and precipitating the late-heavy bombardment
3.8-3.9 billion years – Late heavy bombardment observed in the lunar record
3.5 billion years – Oldest fossil record for life on Earth
4.567 billion years Formation of the solar system
4.54 billion years Accretion of planetesimals into the Earth
4.52 billion years Impact of “Theia” and the formation of the Moon
4 billion years Torrential downpours, cooling of the Earth’s crust, and formation of the first oceans
3.8 billion years Chemical signatures of the earliest life on Earth
3.5 billion years Fossil evidence for the earliest single-cell life
2.5 billion years Oxygenation of the atmosphere due to photosynthesizers
1 billion-750 million years Formation of Rodinia
300-100 million years Formation and dissolution of Pangaea.
Threshold 5 - EMERGENCE OF LIFE
Matter organises into systems that can harness energy to metabolise, reproduce, and adapt to their environments. These are highly complex organic systems capable of self-maintenance with the intake of food energy: amino acids form proteins; nucleic acids make up genetic material; phospho-lipids form permeable membranes. Similar forms are replicated based on genetic material passed from generation to generation. Replication of forms permit change through interaction of the system with the environment. We are not sure how life and DNA originated but it occurred in a chemically diverse environment with water, gentle energy flows, and no free oxygen.
4.56 billion years – Formation of the solar system
4.54 billion years – Formation of the Earth
4 billion years – Torrential downpours lasting millions of years form the Earth’s oceans, allowing chemicals to form in a liquid environment
3.8 billion years – First chemical impressions of single-cell life
3.5 billion years – The oldest fossil evidence for life
2.5 billion years – Photosynthesizers increase percentage of oxygen in the Earth’s atmosphere, less resistant organisms die off
1.7 billion years – Evolution of the first eukaryotes
1.5 billion years – Sexual reproduction
1 billion years – First evidence of multicellular organisms.
Threshold 6 - HUMANS IN NATURE - NATURA
70 M BP – Meteor hits Yucatan Peninsula killing dinosaurs and creating mammalian radiation with primates
3 M BP – Appearance of tools
200-150,000 BP – Appearance of Homo sapiens with with capacity for cultural as well as evolutionary change and knowledge accumulation.
Threshold 7 - HUMANS IN AGRICULTURAL LANDSCAPES - AGRARIA
Palaeolithic man had tools, religion and art but the lifestyle of the hunter-gatherer favoured small groups when large groups could harness the benefits of scale. Agriculture arose independently after the last Ice Age in regions where there were amenable climatic conditions and access to domesticable animals and plants. Crops that could be stored were a source of energy that allowed populations to grow and settled families did not need to carry children. Settled communities produced task specialization and more sophisticated technology, division of labour, hierarchical social structures, scribes to write and maintain commercial and other records, local and external markets. The spaces where people lived and worked were now created by humans who had now moved out of nature.
Threshold 8 - HUMANS IN RURAL & URBAN LANDSCAPES - MODERNITY - INDUSTRIA
The Industrial Revolution (typically 1750-1850 but now expanded to about 300 years) encompasses the transition from subsistence living to mechanization, wealth per capita, and growth with energy as a crucial factor. Energy sources change from wind, horses and water to fossil fuels with a redistribution of labour, information, goods, and capital. Historians are unsure about whether culture and social factors or materials and economic factors are more important in this transition which involves at least five major changes:
Our interpretation of these events falls into two extreme camps: an optimistic view that sees industrialization as the source of liberty, wealth, and happiness with people generally better educated and more healthy, and a pessimistic view that sees it as a means of oppressing peasants, workers, and native populations, the source of climate change and environmental degradation and also the source of ultimate doom of growth is not contained within environmental limits.
First published on the internet – 1 March 2019