The foundation population of the humans that today inhabit the world are the survivors of what appears to be an evolutionary bottleneck caused by a global catastrophe during the period that begins around 90,000 BCE.

The Toba supereruption (Youngest Toba Tuff or simply YTT), a supervolcanic eruption that occurs some time between sixty-nine thousand and seventy-seven thousand years ago at Lake Toba in Sumatra, Indonesia, is recognized as one of the Earth's largest known eruptions and is the most closely studied supereruption.

The related catastrophe hypothesis holds that this event plunged the planet into a six-to-ten-year volcanic winter and possibly an additional one thousand-year cooling episode.

This change in temperature results in the world's human population being reduced to ten thousand or even a mere one thousand breeding pairs, creating a bottleneck in human evolution.

Consistent with the Toba catastrophe theory, evolutionary biologist Richard Dawkins has postulated that human mitochondrial DNA (inherited only from one's mother) and Y chromosome DNA (from one's father) show coalescence at around one hundred and forty thousand and sixty thousand years ago, respectively.

In other words, all living humans' female line ancestry traces back to a single female (Mitochondrial Eve) at around one hundred and forty thousand years ago.

All humans can trace their ancestry with certainty via the male line back to a single male (Y-chromosomal Adam) at ninety thousand to sixty thousand years ago.

An asteroid strikes northern Arizona, the impact releasing energy equivalent to three-and-a-half million tons of TNT.

Probably one hundred feet (thirty meters) in diameter, weighing sixty-three thousand metric tons and traveling five to ten miles per second (eight to sixteen kilometers per second), most of the object vaporizes, but blasts out a bowl-shaped depression six hundred feet (one hundred and eighty meters) deep and 0.72 miles (1.2 kilometers) in diameter, surrounded by a rim one hundred and sixty feet (fifty meters) high.

Barringer Meteor Crater, as the impact site is called, is named for American engineer Daniel M. Barringer, who will theorize in 1905 that the crater was meteoric in origin.

The Transition into the Holocene: Climate Change, Human Migration, and Environmental Transformations

During this epoch, the Northern Hemisphere experienced significant warming, accelerating the deglaciation processand causing rising sea levels as ice sheets continued to melt. This climatic shift marked the transition into the Holocene epoch, a period of relative climate stability following the Last Glacial Maximum (LGM).

Glacial Retreat and Human Recolonization

• Land ice receded from Denmark and southern Sweden, opening up new habitable territories.
• Human populations, previously confined to refuge areas, began repopulating Eurasia as ice sheets withdrew.
• For the first time, humans crossed Beringia into North America, initiating the peopling of the Americas.

The Atlantis Narrative and Speculative Cataclysmic Events

According to Plato's dialogues Timaeus and Critias (circa 360 BCE), the legendary island of Atlantis—described as lying “in front of the Pillars of Hercules” (modern Straits of Gibraltar)—was said to have sunk around 10,000 years earlier along with its advanced civilization.

Some researchers speculate that a cataclysmic event of global significance may have occurred around 9577 BCE, potentially involving:

• Crustal shifts and a possible axial tilt of the Earth
• Mass extinctions of animal species
• The formation of new mountain ranges
• Significant alterations in landmasses
• Massive volcanic eruptions and earthquakes

While no definitive evidence supports a single catastrophic event, glacial retreat after the 11th millennium BCEreshaped landscapes and ecosystems worldwide.

Climate Shifts and Desertification

As the climate stabilized, new regional climate patterns emerged:

• Permanent Mediterranean climates developed in regions such as:

  • The Mediterranean Basin
  • California
  • Southwestern Australia
  • Chile
  • Southwestern Africa

• Desertification gradually encroached upon subtropical regions, fundamentally transforming ecosystems and influencing early human settlements.

This period marked a turning point in human history, as warmer, stable climates allowed for agricultural developments, leading to the eventual rise of Neolithic societies and early civilizations.

The Late Pleistocene-Holocene Megafaunal Extinction Event

The extinction of the cave bear (Ursus spelaeus) around 27,000 years BP was an early indicator of a major wave of megafaunal extinctions that would unfold from the Late Pleistocene into the Holocene. This event saw the disappearance of numerous large mammals, alongside the extinction of our Neanderthal and Denisovan relatives, fundamentally reshaping global ecosystems.

Notable Megafaunal Losses

Among the most iconic species lost during this period were:

• Mammoths and mastodons (Mammuthus and Mammut spp.) – Once dominant herbivores of Ice Age landscapes.
• Saber-toothed cats (Smilodon spp.) – Apex predators that thrived in North and South America.
• Glyptodons (Glyptodon spp.) – Giant armored relatives of modern armadillos.
• Ground sloths (Megatherium and others) – Massive, slow-moving herbivores of the Americas.
• Irish elk (Megaloceros giganteus) – A giant deer with spectacular antlers, found across Eurasia.
• Short-faced bears (Arctodus simus) – One of the largest terrestrial mammalian predators of the Ice Age.

Causes and Consequences

• Climate Change – The warming trend at the end of the Pleistocene altered habitats, leading to vegetation shifts and resource depletion.
• Human Expansion – Advanced hunting strategies and increased predation pressure by expanding human populations likely contributed to megafaunal declines.
• Cascading Ecological Effects – The loss of large herbivores and predators disrupted ecosystems, influencing plant distributions, predator-prey dynamics, and even climate regulation.

This widespread extinction event marked a biological turning point, transitioning Earth from the Ice Age megafauna-dominated ecosystems to those of the Holocene, where smaller, more adaptable species thrived. The impact of this loss continues to influence modern biodiversity and conservation efforts.

Post-Ice Age Faunal Shifts and the Extinction of Megafauna

As the last Ice Age ended, climatic warming and ecological changes led to a gradual replacement of Ice Age megafauna by smaller, more adaptable species. This transition was marked by the northward migration of cold-blooded animals, smaller mammals, migratory birds, and fast-moving species such as the white-tailed deer.

Severe Extinctions in North America

The megafaunal extinctions were particularly severe in North America, where several iconic species were completely eliminated, including:

• Native horses (Equus spp.), which later had to be reintroduced by Europeans.
• Camelids, which had evolved in North America but survived only in South America (as llamas and guanacos) and in Asia (as Bactrian and dromedary camels).

The Role of Climate and Human Hunting

Although similar warming episodes had occurred throughout the last several million years without causing mass megafaunal extinctions, the expansion of advanced human hunters across northern Eurasia and the Americas during this period introduced an unprecedented ecological pressure.

• Overhunting Hypothesis – Highly efficient Upper Paleolithic human hunters, armed with advanced projectile weapons and coordinated hunting strategies, likely accelerated the decline of large mammal populations.
• Climate Stress – The rapid shift from a glacial to interglacial environment led to changes in vegetation, water sources, and habitat availability, further stressing megafaunal species.

A Unique Extinction Event in Prehistory

The interaction between climatic shifts and human expansion distinguishes this extinction event from previous ones. While climate change alone had triggered megafaunal turnovers in earlier epochs, the arrival of human populations introduced a novel, sustained predation pressure, compounding the challenges faced by Ice Age megafauna.

This period marked a transformative shift in global ecosystems, leading to the dominance of smaller, more adaptable species and paving the way for the Holocene’s modern faunal distributions.

Paleo-Indians expand across the American continent around 13,000 years ago, with their hunting potentially contributing to megafaunal extinctions alongside climate change. The traditional 'Clovis First' theory placed initial human arrival at this time via the Beringia land bridge. However, mounting evidence suggests humans reached North America much earlier, possibly 15,000-23,000 years ago.

Two primary migration routes are proposed: an inland ice-free corridor between the Laurentide and Cordilleran ice sheets, and a Pacific coastal route using watercraft. Coastal archaeological evidence would be submerged under post-glacial sea level rise of up to 100 meters.

The timing remains hotly debated, but scholars agree on Central Asian origins and widespread continental habitation during the late glacial period (16,000-13,000 years ago), when warming climates following the Last Glacial Maximum (26,500-19,000 years ago) enabled accelerated deglaciation and population expansion.

The most commonly held perspective on the end of the Clovis culture is that a decline in the availability of megafauna, combined with an overall increase in a less mobile population, led to local differentiation of lithic and cultural traditions across the Americas.

After this time, Clovis-style fluted points were replaced by other fluted-point traditions (such as the Folsom culture) with an essentially uninterrupted sequence across North and Central America.

An effectively continuous cultural adaptation proceeds from the Clovis period through the ensuing Middle and Late Paleo-Indian periods.

It has also been argued that Clovis ended in a very abrupt fashion.

Whether the Clovis culture drove the mammoth, and other species, to extinction via overhunting—the so-called Pleistocene overkill hypothesis—is still an open, and controversial, question.

Climate change, coupled with human predation, disease, and additional pressures from newly arrived herbivores (competition) and carnivores (predation) and isolation, may have made it impossible for many species to reproduce and survive.

It has also been hypothesized that the Clovis culture saw its decline in the wake of the Younger Dryas cold phase.

This 'cold shock', lasting roughly fifteen hundred years, affected many parts of the world, including North America.

It appears to have been triggered by a vast meltwater lake—Lake Agassiz—emptying into the North Atlantic, disrupting the thermohaline circulation.

The end of the Younger Dryas, about eleven thousand years ago, was an interval when the temperature of Greenland warmed by over 5°C in less than a few decades.

A recent hypothesis suggests that one or more extraterrestrial bodies caused the mass extinction and triggered a period of climatic cooling.

Known as the Clovis Comet, or the Younger Dryas impact event, this hypothesis proposes that an extraterrestrial object such as a comet exploded in Earth's atmosphere above North America's Great Lakes region about twelve thousand nine hundred years ago, and significantly affected the human Clovis culture.

Research published in January 2009 argues that there was no extraterrestrial impact, but fails to explain the high levels of metal and magnetic spherules found deep inside the tusks and skulls of mammoths.

Additional evidence of comet impact is the widespread occurrence of microdiamonds and black mats in a layer of sedimentary rocks of that era, but is not reflected in the extinction record.

The Conclusion of the Quaternary Extinction Event (c. 8th Millennium BCE)

The Quaternary extinction event, which began in the mid-Pleistocene, reached its final phase by the start of the 8th millennium BCE. By this time, many of the iconic Ice Age megafauna had disappeared, fundamentally reshaping ecosystems across the globe.

Major Megafaunal Losses

Among the most significant species lost during this period were:

• Megatherium – The giant ground sloths of the Americas, once towering over human hunters.
• Woolly rhinoceros (Coelodonta antiquitatis) – Adapted for Ice Age steppe-tundra, but unable to survive post-glacial warming.
• Irish elk (Megaloceros giganteus) – Famous for its massive antlers, which may have been a factor in its extinction.
• Cave bear (Ursus spelaeus) – A large Ice Age omnivore, extinct by 27,000 years BP, foreshadowing later megafaunal extinctions.
• Cave lion (Panthera spelaea) – One of the largest predatory cats of prehistoric Europe and Asia.
• Saber-toothed cats (Smilodon and Homotherium) – Iconic apex predators that disappeared with declining megafaunal prey.

The Extinction of the Mammoth and Equids

• Mammoths (Mammuthus primigenius) vanished from Eurasia and North America around this time.
• However, isolated populations on Wrangel Island (Arctic Ocean) survived until around 1650 BCE, among the last remnants of the Ice Age giants.
• Equidae (horses and related species) disappeared entirely from North America, where they had evolved.
• While horses, donkeys, and zebras persisted in Africa and Eurasia, wild horses in the Americas vanished, only to be reintroduced by humans in the 16th century CE.

Causes of the Final Extinctions

The final wave of Quaternary extinctions is attributed to two primary factors:

1. Climate Change

   • The end of the Ice Age caused habitat shifts, reducing grazing lands for megafauna.
   • Rising temperatures and changing precipitation patterns disrupted ecosystems that large herbivores depended on.

2. Human Expansion and Overhunting

   • Advanced human hunting techniques (e.g., mass kills, fire-driven hunts, and spears with stone points) increased predation pressure.
   • Human presence often correlated with the disappearance of large prey species, particularly in North and South America.

The Legacy of the Quaternary Extinction

• This massive loss of megafauna reshaped global ecosystems, leaving many regions without their largest herbivores and predators.
• It marked a critical turning point in Earth's biological history, influencing later human societies, as they shifted from big-game hunting toward domesticated animals and agriculture in the Holocene.
• Some species that disappeared in the wild, like the horse, would later be reintroduced and domesticated, altering human civilization forever.

The Quaternary extinction event was one of the most profound biological transitions in prehistory, signaling the end of the Pleistocene megafaunal era and the beginning of the human-dominated Holocene epoch.

The Boreal Period: A Transitional Phase in Holocene Climate (c. 9500–7000 BCE)

The Boreal Period (c. 9500–7000 BCE) represents a key transitional phase in the Holocene paleoclimate, situated between the Younger Dryas—the last cold snap of the Pleistocene—and the Atlantic Period, which ushered in warmer and moister conditions than those of the present day.

Although the Boreal climate varied over time, it generally resembled modern conditions, with fluctuating temperatures and precipitation patterns. However, ice core data suggests that around 7911 BCE, a series of seven massive volcanic eruptions—from unknown locations—triggered a prolonged cooling event, which lasted for several centuries and ended around 7090 BCE.

The Transition to the Holocene Climatic Optimum

As the Boreal Period faded, it gave way to:

• The Neolithic Subpluvial (also known as the Holocene Climatic Optimum or Holocene Wet Phase)—a prolonged wet and rainy period that dramatically affected northern Africa, transforming what is now the Sahara Desert into a lush, habitable environment.
• The Atlantic Period, the warmest phase of the Holocene, coinciding with the Neolithic Subpluvial and further shaping the rise of early human civilizations through agriculture and permanent settlement expansion.

Glacial Retreat and Rising Sea Levels in the Holocene

The Holocene Epoch is characterized by the gradual retreat of glacial ice, which reshaped landscapes worldwide. However, between 12,000 and 5000 BCE, massive inland flooding occurred in various regions, leading to abrupt sea level rises.

These rising waters significantly altered coastal landscapes, forcing human populations to migrate inland and adapt to changing environmental conditions. Such rapid shifts may have contributed to oral traditions and flood mythsfound in various ancient cultures, reflecting the profound impact of these climatic events on early human societies.

The Boreal Period thus stands as a pivotal era, bridging the Ice Age and the Holocene's stable climate, setting the stage for human expansion, agriculture, and the development of early civilizations.

A sudden decrease in global temperatures occurred approximately eight thousand two hundred years before the present, or around 6200 BCE, and lasted for the next two to four centuries, an event that climatologists have named he 8.2-kiloyear event.

Swiss botanist Heinrich Zoller first identified a rapid cooling event in 8200 BP in 1960; he named the it the Misox oscillation (for the Val Mesolcina); it is also known in Norway as the Finse event.

Bond, et al., argued that the origin of the 8.2 kiloyear event is linked to a fifteen hundred-year climate cycle; it correlates with Bond event 5.

Milder than the Younger Dryas cold spell that preceded it, but more severe than the Little Ice Age that will follow, the 8.2 kiloyear cooling is a significant exception to general trends of the Holocene climatic optimum.

The strongest evidence for the event comes from the North Atlantic region; the disruption in climate shows clearly in Greenland ice cores and in sedimentary and other records of the temporal and tropical North Atlantic.

It is less evident in ice cores from Antarctica and in South American indices.

The effects of the cold snap are global, however, most notably in changes in sea level during the relevant era.

The initial meltwater pulse may have raised sea levels by as much as 1.2 meters (four feet), but the cooling that followed allows a glacial advance and consequent marine regression.

After two centuries, or by eight thousand years before the present (6000 BCE), global sea level had dropped by fourteen meters (forty-six feet).

After this point, however, milder climate conditions reasserted themselves; by seven thousand eight hundred years before the present (5800 BCE), the global climate returned to pre-event levels.