CONTINGENCY AND CONTINUITY IN EARTH HISTORY AND BIG HISTORY
One such question, common to all the component fields, may concern the role of contingency in history - a topic with a long pedigree in philosophy. A consideration of contingencies makes it clear that our particular world is the extraordinarily improbable result of what actually did happen, against all likelihood, in history. The particular physics we know emerged during the Big Bang for no known reason. The nature and motions of stars like the Sun are the result of completely unpredictable many-body orbital interactions. Earth could have had no moon, two moons, or have been a moon. The supercontinent cycle happened as it did because of the particular polarity that chanced to happen at the initiation of subduction. The fish that gave rise to land mammals might have had six lobe fins rather than four, so that intelligent tool-using mammals could have walked upright sooner and more easily, and have looked like centaurs. The 65-Ma mass extinction would not have happened if the bolide had been a few minutes ahead or behind in its orbit and missed the Earth; it would have been a different extinction if the bolide had been a few seconds ahead or behind and missed the Yucatán carbonate platform. Human history is notoriously contingent, and strongly influenced by battles whose outcome hangs on the most unpredictable chances. Each individual alive today is the infinitesimally improbable result of 1 Gyr of sexual reproduction.
One can also see trends in Big History, especially toward increasing organization and toward more complex physics, chemistry, and biology, with phase changes at the appearance of new regimes (the H-He cosmos, solid planets, organic life, and thinking humans). Would these continuities have ruled in some form, despite the particular contingent details, or are the trends contingent themselves? This philosophical debate gains in generality when viewed in the broader perspective of Big History.