Big History
David Christian
Introducing the idea of Big History
‘ We need a coherent account of how we were created and how we fit into the scheme of things . . . not a fragmented account of reality . . . a change to the view that serious work is restricted to beating to death a well-defined problem in a narrow discipline . . . Frames of any kind exclude more than they reveal. And this is particularly true of the conventional time frames of modern historiography, which normally extend from a few years to a few centuries . . . we desperately need to see humanity as a whole. Accounts of the past that focus primarily on the divisions between nations, religions, and cultures are beginning to look parochial and anachronistic – even dangerous . . . Big History proposes to create a new ‘grand narrative’ just when we have learned the futility, even the danger, of grand narratives . . . large stories provide a sense of meaning ‘
David Christian 2011 – Maps of Time
Introduction – Big History
Today we know more than ever before about ‘everything’. We are living in an Information Age where facts about the world and our collective learning are accumulating at an ever-increasing rate. But how do we fit all these facts together to build a unified account of history and the world using the best available evidence and information?
Every culture has its own origin story. Big History is the human origin story as revealed by science and deep time. It provides us with a long-term explanatory framework for the place of humans in the overall scheme of things (see also worldviews).
Big History[5] examines the preconditions necessary for the existence of planet Earth itself . . . then for life, plants, and people. It looks at how those Goldilocks conditions (the conditions just right for life to exist) emerged and the star stuff that is crucial to life.
What is Big History?
Big History had its origin in the 1980s as an attempt to draw together what we know about the universe, and our place in it. History at this scale is a multidisciplinary subject that combines both science and the humanities. It arose, in part, from the awareness that, at any point in time, what occurs necessarily depends, to a greater or lesser extent, on what happened before. To be ‘complete’, history must take this into account even though, of course, narrow time frames serve specific purposes.
Much of the Big History program was developed by Australian ‘Big Historian’ David Christian.[3]
ChronoZoom
Computer representation of time at all scales from the Big Bang 13.7 billion years ago to the present
Available free here.
Courtesy Wikipedia Commons
Orangeboxes2 – Accessed 21 April 2017
Mainstream history
Where Big History differs from other grand narratives is that it is more science-based and therefore under constant scientific revision.
Most importantly, the perspective of Big History it is not specific to a particular race, religion, or ideology – it is therefore a global (universal) origin story. Christian refers to it as a Grand Unified Theory of History (GUTH).[1]
This web site on plants and people takes as its starting point the context provided to us by Big History. If you find this approach to history appealing or useful then there are many videos about Big History on Youtube. This article provides just a brief introductory outline of their content.
There are several key ideas to the philosophy of Big History.
Analysis & synthesis
There are two general approaches to our study of the world: we can study it analytically, by breaking it down and reducing it to simpler component pieces, or we can study it synthetically by seeing how pieces are integrated into structural and functional wholes. In our individual lives we are constantly assessing the way events and objects around us ‘make sense’ by fitting them into a ‘Big Picture’. Ideally, knowledge accumulation can proceed by a constant to and fro’ between analysis and synthesis.
Big History resists the desire to fragment, reduce, and specialize. Articles on this web site are mostly synthetic and multidisciplinary, trying to unite different subject areas.
The need for synthesis
Many of us have a deep spiritual, psychological, and social desire for an explanation of our lives and their place within the greater whole. This provides grounding and a sense of identity for our lives. Without it there can be disorientation, confusion, and a sense of drift, what French sociologist Emile Durkheim referred to as ‘anomie’. There is also a sense that our education system, rather than providing us with the richest possible preparation for life is, instead, part of our job training.
Higher education has undergone a remarkable reversal. It has gone from having general literacy as its goal, leaving special expertise to form itself later as the outcome of individual interest and experience, to inculcating special expertise as its goal, leaving general literacy to form itself later as the outcome of individual interest.[6]
Big History provides the broad-brush explanation of the place of humanity in the universe that gives history a sense of meaning, purpose, and direction. This web site tries to compensate for the constant desire for more data with the provision of theory to account for that data: it locates plants within a universal context.
The future
Much of human history has involved conflict – over land and territories, resources, dynasties, religions and ideologies. Our world is becoming increasingly one of interconnection and interdependence in spite of counter-trends of autonomy and self-determination.
The better we understand the broad sweep of history, the universe, and the place of humans within it, the better can manage our future. Detailed knowledge of small segments of history cannot give us this perspective. Big History is an opportunity for cultural revision, the reassessment of human meaning and purpose within the boundaries of space and time and a vision for the future.
A world view
We are indeed stardust – the atoms and molecules in our bodies came from the universe and will return to it; in terms of our simple physics and chemistry, but not our biology, we share the age of the universe at 13.8 billion years
Traditionally it is religions that have provided accounts of creation the world views that give us identity . . . telling us how humans arose and where they fit into the scheme of things. Skeptics are justifiably suspicious of grand narratives or world views given the disastrous conflicts that have arisen out of uncompromizing ideologies and grand visions.
Among the tasks of Big History there is the assessment of the smoothness with which explanations intersect and the detection of anomalies – where there are major gaps in our knowledge – and understanding common themes that run through the overall account.
David Christian identifies four key factors in the Big History account: the underlying role of energy within all systems; the emergence of increasing complexity; the origin of new properties at particular scales of material organisation; and the Goldilocks principle, the presence of those critical conditions needed to cross physical thresholds.
Christian suggests that three key factors have influenced human history: access to and control of resources; growth in population; and increase in social complexity (social organisation).
Natural selection is the driver of biological change but significant change in human lives has occurred, not just by genetic inheritance, but by the transmission of cultural information using symbolic languages including the written and spoken word, and mathematics.
Timelines
Christian suggests that one major reason why long-term history has become more scientific is because of the sudden improvement in dating techniques.
The Chronometric Revolution
Three centuries ago our collective human knowledge of ancient history – meaning the period to about 1000 BCE – was restricted to four written sources: the Indian Vedas, the Chinese Five Classics, the Hebrew Bible and the Greek poet Homer.
The Bible, it was assumed, presented literal historical truth, and with little science to prove otherwise, the claim by Archbishop of Ireland James Ussher (1581-1656) that the world was created in 4004 BCE was widely believed.
Archaeology changed all this when French linguists in the 1820s unlocked the secrets of Egyptian hieroglyphics, taking (Western) history back to about 3000 BCE. British scholars of the 1840s then mastered the Old Persian, Assyrian, and Babylonian languages of Mesopotamia. The geological evidence of rocks, which was dismissed by religious belief, became scientifically accepted in the stratigraphy of the 1920s. The 19th century had unearthed pre-classical civilizations and the investigation of human evolution.There has, since WWII, been a little-acknowledged Chronometric Revolution as scientific technology has expanded our biologically given senses at both the macro- and micro-scales.
‘. . . at the end of the nineteenth century it was still impossible to assign reliable absolute dates to any events before the appearance of the first written records’ but ‘There now exist no serious intellectual or scientific or philosophical barriers to a broad unification of historical scholarship’.
The Chronometric Revolution over the last few decades has allowed us to date the age of the universe, individual rocks and fossils, archaeological remains, and the divergence of lineages in biological evolution.
In 1905 Ernest Rutherford pioneered the study of radioactive decay over time in what would subsequently develop, after 1945, into what we now call radiometric dating. Geochronology, the dating of rocks, uses the constant rate of decay of radioactive impurities for dating. The half-life of radioactive isotope carbon fourteen (C14) is relatively short at 5,730 years and this is reliable for dating organic remains up to 50,000 years old which conveniently covers a large portion of the time during which anatomically modern humans migrated across the globe.
Willard Libby pioneered radiocarbon dating in the 1940s and received Nobel prize for this work in 1960. This has transformed the study of archaeology. Accelerator mass spectrometry extending this period to 80,000 years, and this time span was expanded again with the advent of thermos-luminescence which can date objects over a period of several hundred years.
Potassium/Argon dating is used to measure the age of the earth and therefore an invaluable tool for geology.
Since the elucidation of the structure of DNA by Watson and Crick in 1953 genetic analysis has vastly improved such that we can now date with increasing accuracy the times of evolutionary divergence of branches on the tree of evolution.
The discovery of cosmic background radiation in 1964 has enabled us to date the current age of the universe at 13.8 billion years.
The psychological and intellectual leap that has occurred since the 19th century is vast moving from a ‘biblical framework’ to one in which:
. . . the universe began 13.72 billion years ago, life 4 billion years ago, hominins 6 million years ago, Homo 2 million years ago, anatomically modern humans c. 300 kya, behaviourally modern humans (about) 100 kya, settled agriculture 10 kya, cities 5 kya – none of these formerly known or even guessed.[7]
History
History & science
The once clear distinction between science and non-science is dissolving. We can no longer sustain the view that history deals with unpredictable and contingent processes and is largely a study of thoughts and motives while science deals with law-like predictability and regularity. There is, rather, across-the-board application of scholarly rigour within domains of knowledge. Both science and history depend on evidence. Certainly science involves empiricism as model-testing by observation to form predictions and law-like claims in a slightly different way from history. But this is hardly a critical distinction as social science uses a similar methodology.
Big History factors
Increasing complexity
In the course of the history of the universe, there has been the emergence of objects of increasingly complex structure and organization. This is in apparent localized defiance of the second law of thermodynamics (the law of entropy) which tells us that the overall trajectory of the universe is to rundown – energy cannot be created or destroyed only transformed, and in transformation it degrades. Structure must eventually disperse.
The early tiny irregularities in the universe (wrinkles) gave rise to the thermodynamic disequilibrium that allowed gravity to clump matter into stars and galaxies, followed by life and human beings.
Scale
History examines events as they occur in both spaces (places) and times. When expressed in this way we see that the key ‘content’ of history is not just time but space as well, in other words, scale. This is like looking down a microscope. Just as looking down a super microscope might reveal first an insect, then its leg, then the anatomy of the leg, as we narrow the historical focus so the different scales bring different factors, aspects or interpretations into view.
The scale of study we choose depends on what we want to learn. Does history begin with the Big Bang, the emergence of humans from ape-like ancestors, or does the use of written language provide a convenient demarcation between history and pre-history (say, around 3000 BCE and after), or is it the advent of modern science and industrial society (say, from around 1500) . . . what would you choose?
The temporal scale we choose for our history can change the mode of historical analysis. If we consider human history from the time of the Big Bang to the present our periodization will be of wide time frames relating to the long-term history of humans and the universe. We would not look to historians to information of these changes we would look primarily to scientists, essentially physicists and anthropologists. At this scale history is Big History. When we look at history in terms of the full span of human history, again it is not historians that we look to for Enlightenment but archaeologists, palaeogeneticists, evolutionary biologists, and anthropologists. It is only when we consider the shorter time frames that humanitarian insights of traditional historians can be brought to bear.
In general terms, the longer the time frame (millennia) the more important become large impersonal forces like geography: ‘what differs is not people but places’. Over the medium-term, say centuries, we tend to focus on change due to political, economic and cultural factors. Short-term history is inclined towards particular places, events, and people.
Big History is large-scale, covering all time and space, what happened in your life is small-scale. Big history encourages historians to work on many scales; it counters our temptation to focus on human agency and whim that gives history its strong sense of contingency . . . ‘At the very large scales, even in human history, structure begins to trump agency’. It resists the tendency to view all history from the perspective of the present, for example, the view that ‘the Stone Age was a preamble to history, a dystopian era of stasis before the happy onset of civilization, and the arrival of nifty developments like chariot wheels, gunpowder, and Google’ (Wikipedia). The general assumption that history begins with the written word looks parochial today. [3]
Globalization
It takes the world to build a laptop computer in terms of the social organization and resources that are required. It is the uneven distribution of human, mineral and organic resources across the planet that creates todays trade network. In general the more complex the system and greater the encouragement of innnovation the greater the wealth generated but this can be exported as occurred with China. Science and technology entail embedded knowledge, the average automobile today linked to 100,000 patents. After 1950 there was a Great Acceleration in human population, economic activity, and per capita GDP.
The rate of environmental, social, and economic change has closely matched the rate of increase in human population – 10 million in 10,000 BCE, 135 million in 1500, and 7.5 billion in 2017. The population explosion that occurred between 1700 and 1900 was accompanied by a massive increase in technological capacity as a consequence of the Scientific and Industrial Revolutions that occurred through the Age of Discovery which was marked by northwestern European maritime colonial expansion away from the old Mediterranean trade routes and into the Atlantic, Indian, and Pacific Oceans to develop a truly global economy dominated by European (mostly British) values, traditions, and social institutions. Collectively this has become known as the Great Divergence.
Between 1960 and 2000, even after two world wars, the population would again double in the Great Acceleration whose technology now created a transport and communication revolution as part of an electronic age in a world strongly influenced by America and American culture. The last decade or so has seen China adopt a market economy and rapid economic growth.
Big history assumes that research into analytic detail, whether historical or scientific, takes place within a broader framework of understanding (a grand narrative) and that it is only from the vantage point of this broader framework of understanding that policy is derived and practical management decisions are taken.
Big history contributes towards a consensus empirically-based grand narrative that is emerging from the constant interplay between fine detail (analysis) and overview (synthesis) that is part of the constant reinterpretation of both history and science. It steps back to examine the long-term factors that have shaped human history.
Key points
- Big history seeks to understand the integrated history of the Cosmos, Earth, Life, and Humanity, using the best available empirical evidence and scholarly methods: it is an internationally shared account of the universe and its contents, contributing to the scholarship of everything
- Four key factors that have influenced the Big History account of the universe:
1. the crucial role of energy in all systems
2. the origin of new properties at particular scales of material organization
3. Goldilocks principle, the presence of those critical conditions needed to cross physical thresholds.
4. the emergence of increasing complexity
1. access to and control of resources
2. growth in human population
3. increase in social complexity (social organization).
- Natural selection is the driver of biological change but significant change in human lives has occurred, not just by genetic inheritance, but by the transmission of cultural information using symbolic languages that include the written and spoken word, and mathematics.
- Since WWII there has been a Chronometric Revolution adding much-increased security to scientific knowledge by allowing us to date the age of the universe, individual rocks and fossils, archaeological remains, and the divergence of lineages in biological evolution.
- The distinction between arts and humanities is dissolving. We can no longer sustain the view that history deals with unpredictable and contingent processes and is largely a study of thoughts and motives while science deals with law-like predictability and regularity. There is, rather, across-the-board application of scholarly rigour within domains of knowledge. There is now no serious intellectual or scientific barrier to a broad unification of historical scholarship’.
- Big History divides the history of the universe into eight ‘thresholds’ with just three of these involving humans (see below) to which I add a fourth, Informatia, the transition threshold from fossil fuels to renewable energies.
Big History Thresholds
Big History divides the history of the universe into eight ‘thresholds’ with just three of these involving humans.
Those thresholds encompassing human history are discussed in more detail later under the headings Natura, Agraria, and Industria to which I have added a fourth, Informatia. As an introduction to human history I suggest reading the article History in 10,000 words.
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
Planet formation:
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.
Timeline of Chronometry
c. 1600 Archbishop of Ireland James Ussher (1581-1656) dates the Creation to around 6 pm on 22 October 4004 BCE according to the proleptic Julian Calendar
1800 – the dating of the collective human knowledge of ancient history is restricted to, essentially, four written sources: the Indian Vedas, the Chinese Five Classics, the Hebrew Bible, and the Greek poet Homer.
1820s – Egyptian hieroglyphics deciphered taking known history back to about 3000 BCE
1840s – British scholars master Old Persian, Assyrian, and Babylonian languages of Mesopotamia
1900 – still impossible to assign reliable dates to any events prior to the written record
1905 – Ernest Rutherford pioneers radioactive decay
1939 – Americans L.W. Alvarez and Robert Cornog first use an accelerator mass spectrometer (AMS) in a cyclotron to demonstrate that 3He was stable and that the other mass-3 isotope, tritium (3H), was radioactive. AMS uses smaller sample sizes (c. 50 mg) and has become an advance on radiocarbon dating covering samples ranging from around 80,000 to 100 years old
1940s – radiocarbon dating pioneered by Willard Libby (receives Nobel Prize in 1960). This transforms archaeology, allowing key transitions in prehistory to be dated and applied as geochronology, the dating of rocks, using the constant rate of decay of radioactive impurities e.g.the last ice age and commencement of the Neolithic and Bronze Age in different regions. The half-life of radioactive isotope carbon fourteen (C14) is relatively short at 5,730 years and this is reliable for dating organic remains up to 50,000 years old (conveniently covers much of the period when anatomically modern humans migrated across the globe).
1962 – Émile Zuckerkandl and Linus Pauling notice that the number of amino acid differences in hemoglobin between different lineages changes roughly linearly with time, as estimated from fossil evidence. They generalized this observation to assert that the rate of evolutionary change of any specified protein was approximately constant over time and over different lineages (known as the molecular clock hypothesis, gene clock, or evolutionary clock). It is an important tool in molecular systematics used to determine scientific classifications and study variation in selective forces. Knowledge of rates of molecular evolution in particular lineages also helps estimate the dates of phylogenetic events, including those not documented by fossils. However, as yet it is limited and estimates may vary by 50% or more.
1964 – discovery of cosmic background radiation enables dating age of the universe to 13.8 billion years
1967 – A.C. Wilson promotes the idea of a ‘molecular clock’ – a technique that uses the mutation rate of biomolecules (usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins) to deduce the time in prehistory when two or more life forms (lineages) diverged. Essentially a way of dating the branching points of the evolutionary tree
1969 – molecular clocking applied to anthropoid evolution. V. Sarich and A.C. Wilson find albumin and hemoglobin have comparable rates of evolution, indicating chimps and humans split about 4 to 5 million years ago
molecular anthropology has been extremely useful in establishing the evolutionary tree of humans and other primates
1970s – mitochondrial DNA became an area of research in phylogenetics in the late 1970s. Unlike genomic DNA, it offered advantages in that it did not undergo recombination.
Big History Preview
CrashCourse Big History – 2014
The Sun & the Earth
Human Evolution
The Anthropocene and the Near Future
CrashCourse Big History – 2014 – 12:19
The Origin of the Elements
Jefferson Lab – 2012- 57:32
The Big Bang
Emergence of life
Migrations and Intensification
The Deep Future
Exploring the Universe
The Evolutionary Epic
The Modern Revolution
The history of our world in 18 minutes | David Christian
TEDx – 2011 – 17:40
First published on the internet – 1 March 2019
. . . substantial revision – 22 July 2020
Omega or Swan Nebula
Photograph NASA’s Hubble Space Telescope located about 5500 light-years away in the constellation Sagittarius.
Courtesy Wikimedia Commons – NASA, ESA and J. Hester (ASU) 2003 – Accessed 15 October 2020
