1 The World from the Dawn of Time (c.4.5bn-c.7m bc) In the beginning when God created the heavens and the earth, theearth was a formless void ... - Book of Genesis, 1:1 We should all be grateful for dramatic changes to global climate. Wereit not for billions of years of intense celestial and solar activity, repeatedasteroid strikes, epic volcanic eruptions, extraordinary atmospheric change,spectacular tectonic shifts and constant biotic adaptation, we would not bealive today. Astrophysicists talk of habitable regions around stars that arenot too hot and not too cold as being in the 'goldilocks zone'. The earthis one of many such examples. But conditions have changed constantlyand sometimes catastrophically since the creation of our planet around4.6 billion years ago.1 For almost all the time that the earth has existed, ourspecies would not and could not have survived. In today's world, we thinkof humans as architects of dangerous environmental and climate change;but we are prime beneficiaries of such transformations in the past. Our role on this planet has been an exceptionally modest one.The first hominins appeared only a few million years ago, and thefirst anatomically modern humans (including Neanderthals) around500,000 years ago. What we know of the period since then is patchy,difficult to interpret and often highly speculative. As we get closer to themodern day, archaeology helps us understand more reliably how peoplelived; but to know what they did, thought and believed we have to wait till the development of full-writing systems around 5,000 years ago. Toput that into context, accounts, documents and texts that allow us toreconstruct the past with nuance and detail cover around 0.000001 percent of the world's past. We are not just fortunate to exist as a species,but in the grand scheme of history we are new and very late arrivals. Like rude guests who arrive at the last minute, cause havoc and setabout destroying the house to which they have been invited, humanimpact on the natural environment has been substantial and isaccelerating to the point that many scientists question the long-termviability of human life. That in itself is not unusual, however. For onething, our species is not alone in transforming the world around us, forother species of biota - that is to say, flora, fauna and microorganisms -are not passive participants in or simple bystanders to a relationshipthat exists solely or even primarily between humans and nature. Eachis actively involved in processes of change, adaptation and evolution -sometimes with devastating consequences. This is one reason why some scholars have criticised the idea andthe name of the 'Anthropocene', which prioritises humans into 'adistinguished species' that has claimed the right to identify what is andis not wild, to classify 'resources' as ones that can be used - sustainably orotherwise. Such, argue some, is the 'arrogance that greatly overestimateshuman contributions while downplaying those of other life formsalmost to the point of nonexistence'. For around half the earth's existence, there was little or no oxygen in theatmosphere. Our planet was formed through a long period of accretion,or gradual accumulation of layers, followed by a major collision with aMars-sized impactor - which released enough energy to melt the earth'smantle and create the earliest atmosphere from the resultant exchangebetween a magma ocean and vapour that was anoxic, that is to say,lacking in oxygen. The earth's biogeochemical cycles eventually resulted in a radicaltransformation. Although there is considerable debate about how, whenand why oxygenic photosynthesis occurred, evidence from organicbiomarkers, fossils and genome-scale data suggests that cyanobacteriaevolved to absorb and take energy from sunlight, using it to make sugarsout of water and carbon dioxide, releasing oxygen as a by-product. Newmodels suggest that 1 to 5 billion lightning flashes that occurred per year on early earth may have been the source of large volumes of prebioticreactive phosphorus that played an important role in the emergence ofterrestrial life. Around 3 billion years ago - if not earlier - enough oxygen wasbeing produced to create 'oases' in protected nutrient-rich shallowmarine habitats.6 Whether because of chemical reaction, evolutionarydevelopment, sudden superabundance of cyanobacteria, volcaniceruptions or a slowdown in the earth's rotation (or a combination ofall five), atmospheric oxygen levels accumulated rapidly around 2.5-2.3billion years ago, resulting in an episode known as the Great OxidationEvent. This was a key moment that paved the way for the emergence ofcomplex life as we know it. It also led to dramatic changes in climate, as rapidly increasing oxygenreacted with methane, producing water vapour and carbon dioxide.Alongside the effects of a supercontinent being formed from thecollisions of landmasses, the earth's greenhouse was weakened, leadingto the planet being covered completely in ice and snow.8 Changes in theearth's orbit around the sun, known as the Milankovitch cycle, may alsohave played a role in this process.9 So too might giant meteorite impactswhich not only threw up debris into the atmosphere that blocked thesun's light and heat but also played an important role in the formationof the continents.The glacial episodes may have been weaker orstronger over the course of several hundred million years, but in generalthe effect of 'Snowball Earth' was so dramatic that some scientists referto this period as a whole as a 'climate disaster'. This process was precarious and complex, and is the subject ofconsiderable advances in current research. As with later glaciations,however, it resulted in profound changes for the planet's plant and animallife. One outcome appears to have been the evolution of small organismsinto larger sizes, capable of moving at faster speeds to compensate forthe high viscosity of cold seawater.14 It has recently been suggested thatthe formation of 8,000-kilometre long belts of 'supermountains' mayhave played a role in the rise of atmospheric oxygen and in stimulatingbiological evolution as a result of phosphorus, iron and nutrients beingdeposited into oceans as mountains eroded over the course of hundredsof millions of years. The fossil record of complex, macroscopic organisms begins with theEdiacara Biota period which started 570 million years ago and which saw at least forty recognised species developing into multicellular animals thatwere symmetrical - presumably helpful for functions such as mobility.16 Itmarked a period of extraordinary diversification in the variety of animalsliving in the oceans and in their evolution, development and adaptation,with some creatures like trilobites developing respiratory organs on theirupper limbs. Near the end of the Ordovician period, around 444 million years ago,a sudden cooling, perhaps triggered by tectonic shifts that produced theAppalachian mountains, led to sharp falls in temperature and initiatedshifts in deep ocean currents, as well as declines in sea level that shrankhabitats for marine planktonic and nektonic species. That coolingproduced one pulse of extinction; another came when temperaturesmoderated, sea levels rose and ocean current patterns stagnated, with aresultant sharp fall in oxygen levels.18 Traces of mercury and indicationsof significant acidification suggest that volcanic activity was a key factorin the second stage of a process that ultimately brought about theextinction of 85 per cent of all species. As the moon used to be much closer to the earth - perhaps half thedistance away that it is today - these forces were considerably strongerand therefore had a greater impact on the earth's climate and alsoperhaps on its wildlife: recent modelling suggests that big tidal rangesmay have been responsible for forcing bony fish into shallow poolson land, thereby prompting the evolution of weight-bearing limbsand air-breathing organs.21 The moon played a role not only in thetransformation of the earth, in other words, but also in the developmentof life on this planet. Excerpted from The Earth Transformed: An Untold History by Peter Frankopan All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.
