Origin Story: A Big History of Everything

by David Christian

Land-dwelling plants had a particularly large impact on the atmosphere, as they inhaled carbon dioxide and exhaled oxygen. Levels of atmospheric oxygen rose fast after the Ordovician period, increasing from about 5 to 10 percent of the atmosphere to levels much higher than they are today, perhaps to 35 percent, before stabilizing.

Since about 370 million years ago, oxygen levels have mostly remained between 17 percent and 30 percent of the atmosphere.

fires cannot ignite if oxygen levels fall much below 17 percent.

Corals are really vast symbiotic colonies of tiny, genetically identical invertebrate animals. At a stretch, we might regard them as vast, sprawling animals with a hard but somewhat shapeless skeleton. Each coral hosts colonies of single-celled photosynthesizing organisms that supply it with energy.

it seems likely that very large organisms flourished best when oxygen levels were highest, which usually meant during periods of low carbon dioxide levels and cooler climates.

Hell Creek Formation, in Montana and Wyoming, you can find fossils of fish whose gills are full of glass from the asteroid impact.

The surface of Earth would have been in total darkness for a year or two, shutting down photosynthesis,

A few years after the impact, the wretched survivors could start photosynthesizing and breathing again, but they did so in a hot greenhouse world.

Within half a million years, there were cow-size herbivorous mammals and equally large mammalian carnivores. There were also primates, members of the order of tree-dwelling, fruit-eating mammals from which we are descended. Though the first primates already existed in the world of dinosaurs, they flourished only after the dinosaurs had left the scene.

There was one more crisis to be survived before mammals could take over the Earth. That was the Paleocene-Eocene thermal maximum (PETM, for lovers of acronyms), a short, sharp shock of greenhouse warming at the border between the Paleocene and Eocene epochs, about fifty-six million years ago. It was damaging enough to drive many species to extinction. The PETM is of interest today because it is the most recent period of rapid greenhouse warming in Earth’s history,

The amounts of carbon dioxide released into the atmosphere during the PETM were similar to those being released today by the burning of fossil fuels, and fifty-six million years ago, the result was an increase of between f...

Whatever the precise causes, the cooling trend that began about fifty million years ago has continued to the present day. About 2.6 million years ago, at the beginning of the Pleistocene epoch, the world entered the current phase of regular ice ages. The world had not been this cold for 250 million years, since Pangaea itself had split apart at the end of the Permian period. Fifty million years ago, in this post-dinosaur, post-PETM world of chilly and erratic climate changes, our primate ancestors evolved.

In the past, whole groups of organisms, such as the cyanobacteria, have changed the biosphere, but never before has a single species wielded such power.

Genetically, though, we are more homogenous than our closest living relatives, the chimps, gorillas, and orangutans. We just haven’t been around long enough to diversify much. Besides, we are extraordinarily sociable, and we love to travel, so human genes have moved pretty freely from group to group.

In most mammal species, the cortex accounts for between 10 percent and 40 percent of brain size. In primates, it accounts for more than 50 percent, and in humans for as much as 80 percent.

In human bodies, the brain uses 16 percent of available energy, though it accounts for just 2 percent of the body’s mass.

There are species of sea slugs that have mini-brains when they are young. They use them as they voyage through the seas looking for a perch from which they can sieve food. But once they’ve found their perch, they no longer need such an expensive piece of equipment so… they eat their brains. (Some have joked, cruelly, that this is a bit like tenured academics.

humans, chimps, and gorillas shared a common ancestor until about eight million years ago, at which point the ancestors of modern gorillas decided to go their merry way. Humans and chimps shared a common ancestor up to about six or seven million years ago. In other words, somewhere in Africa six or seven million years ago, there existed a creature from which modern humans and chimpanzees are both descended.

until as recently as twenty or thirty thousand years ago, several different species of hominins cruised the savannas of Africa and Eurasia at the same time. The recent disappearance of other hominin species as we humans took up more and more land and resources is a sign of how dangerous we are.

good evidence for systematic control of fire appears only from about eight hundred thousand years ago and becomes quite common only after about four hundred thousand years ago.

There is an evolutionary mechanism known as competitive exclusion that explains why two species can never share exactly the same niche.

The largest catastrophe of this kind occurred about seventy thousand years ago. Genetic evidence shows that the number of humans suddenly fell to just a few tens of thousands, only enough to fill a moderate-size sports stadium. Our species came close to extinction. The catastrophe may have been triggered by a massive volcanic eruption on Mount Toba in Indonesia that pumped clouds of soot into the atmosphere, blocking photosynthesis for months or years and endangering many species of large animals.

At sites like Mezhirich, people built huge marquee-like tents, using skins stretched over a scaffolding of mammoth bones, and warmed them with internal hearths. They hunted mammoths and other large animals and stored meat in refrigerated pits for recovery during the long cold winters.

During the Pleistocene epoch, which encompasses the two million years since the evolution of Homo erectus, there were many ice ages. They normally lasted for one hundred thousand years or more, with briefer warm periods, or interglacials, between them. The period we live in now is a warm interglacial that began ten thousand years ago, at the start of the Holocene epoch.

The coldest period of the last ice age was from about twenty-two thousand to eighteen thousand years ago.

it seems more likely that the first Australians arrived from communities long established in Asia.

At present, the earliest firm evidence for the presence of humans in North America dates to about fifteen thousand years ago.

In Australia, Siberia, and North America, the megafauna vanished not long after the arrival of humans. Perhaps, like the dodo in Mauritius, the megafauna didn’t fear our ancestors enough, unlike African megafauna, which had coevolved with humans and knew how dangerous we could be.

Farming was a mega-innovation, a bit like photosynthesis or multicellularity.

A human can deliver at most about 75 watts of energy, while a horse or ox can deliver up to ten times as much.

In the year 2000, the total biomass of all wild land mammals was about one-twenty-fourth that of domesticated land mammals.

By the time farming got going, humans were so widely dispersed that events in one part of the world had little impact elsewhere.

islands farther to the east and south (including New Zealand, Hawaii, and Easter Island) were settled during a remarkable series of seaborne migrations that began just thirty-five hundred years ago.

as independent human communities accumulated more technological and ecological knowledge, there was a high probability, wherever they were, that they would eventually use the knowledge they had accumulated as foragers to develop farming techniques. But they were likely to do so only if they needed the extra resources that farming could provide because, after all, farming was hard work and it meant changing a community’s entire way of life.

Graphs of average world temperatures over the past sixty thousand years show clearly the remarkable climatic stability of the past ten thousand years, even though variations were greater away from the tropics.

Foragers were attracted to regions like the Fertile Crescent, areas that had plants and animals that were ripe for domestication.

by the time agriculture began to spread, large domesticable herbivores could be found only in Afro-Eurasia.

By its very nature, farming required a manipulative attitude to the environment.

Populations rose fast as farming methods improved and farming spread. It had taken at least one hundred thousand years for human populations to reach five million, at the end of the last ice age. By five thousand years ago, human numbers had quadrupled, rising to about twenty million. By two thousand years ago, there were two hundred million humans, forty times the number at the end of the last ice age.

Five thousand years ago, in the southern Mesopotamian city of Uruk, someone compiled a list of a hundred different special roles, the Standard Professions List.

There is a six-thousand-year-old burial site near Varna on the Black Sea that contains more than two hundred tombs. Many of the dead were buried with nothing or with just a few simple objects, but about 10 percent of the graves held much more; one contained over a thousand objects, most of them made of gold, including bracelets, copper axes, and even a penis sheath.2 This is a very familiar triangle of wealth, with an elite population of about 10 percent and one person at the very top, while most people lived close to subsistence.

There is surely some caricature here, but we have plenty of evidence that extortionate methods were used in all agrarian civilizations to maintain order and to extract labor and resources from the majority of the population.

Jericho, one of the oldest sites of continuous settlement anywhere in the world, was first settled in Natufian times because it had a well that never ran dry. By nine thousand years ago, Jericho had evolved into a town of perhaps three thousand people.

As Karl Marx noted, peasants had no more unity than potatoes in a sack.

By two thousand years ago, humans were using seventy times the amount of energy they consumed at the end of the last ice age. This colossal energy bonanza from farming paid for population growth, for entropy’s various complexity taxes, and finally for the wealth of the rich and powerful. There is little sign that it improved the lives of most humans.

The French economist Thomas Piketty has estimated that in most European countries as late as 1900, 1 percent of the population owned about 50 percent of national wealth, and 10 percent of the population accounted for 90 percent of national wealth.

There was really no middle class in the modern sense because “the middle 40 percent of the wealth distribution were almost as poor as the bottom 50 percent. The vast majority of people owned virtually nothing, while the lion’s share of society’s assets belonged to a minority.”

By 1400 CE, human populations had grown from about five million at the end of the last ice age to one hundred times as many, or almost five hundred million people.

David Wootton describes the change vividly. In Shakespeare’s time, even the most educated Europeans generally believed in magic and witchcraft, in werewolves and unicorns; they believed that Earth stood still and the heavens turned around it; that comets portended evil; that the shape of a plant advertised its medicinal powers because God had designed it to be interpretable; that The Odyssey was a true history.

the 2016 Global Slavery Index estimated that more than forty-five million humans today are living as slaves.