An asteroid strikes northern Arizona, the impact…

The descendants of the immigrants to West Asia who had remained in the south (or taken the southern route) had spread generation by generation around the coast of Arabia and the Iranian plateau until they reached India.

One of the groups that had gone north (east Asians were the second group) had ventured inland and radiated to Europe, eventually displacing the Neanderthals.

They had also radiated to India from Central Asia.

The former group headed along the southeast coast of Asia, reaching Australia between fifty-five thousand and thirty thousand years ago, with most estimates placing it about forty-six thousand to forty-one thousand years ago.

Sea level is much lower during this time, and most of Maritime Southeast Asia is one land mass known as the lost continent of Sunda.

The settlers probably continued on the coastal route southeast until they reached the series of straits between Sunda and Sahul, the continental land mass that was made up of present-day Australia and New Guinea.

The widest gaps are on the Weber Line and are at least ninety kilometers wide, indicating that settlers had knowledge of seafaring skills.

Archaic humans such as Homo erectus never reached Australia.

If these dates are correct, Australia was populated up to ten thousand years before Europe.

This is possible because humans avoided the colder regions of the North favoring the warmer tropical regions to which they were adapted given their African homeland.

Another piece of evidence favoring human occupation in Australia is that about forty-six thousand years ago, all large mammals weighing more than one hundred kilograms suddenly became extinct.

The new settlers were likely to be responsible for this extinction.

Many of the animals may have been accustomed to living without predators and become docile and vulnerable to attack (as will occur later in the Americas).

Some settlers cross into Australia, while others may have continued eastwards along the coast of Sunda eventually turning northeast to China and finally reaching Japan, leaving a trail of coastal settlements.

This coastal migration leaves its trail in the mitochondrial haplogroups descended from haplogroup M, and in Y-chromosome haplogroup C.

Thereafter, it may have become necessary to venture inland, possibly bringing modern humans into contact with archaic humans such as H. erectus.

As humans develop more advanced skills and techniques, evidence of early construction begins to emerge.

Fossil remains of Cro-Magnons, Neanderthals, and other Homo sapiens subspecies have been found alongside foundation stones and stone pavements arranged in the shape of houses, suggesting a shift toward settled lifestyles and increasing social stratification.

In addition to building on land, early humans also develop seafaring technology. The proto-Australians appear to be the first known people to cross open water to an unseen shore, ultimately peopling Australia—a remarkable achievement in early maritime exploration.

Recent genetic studies suggest that Australia and New Guinea were populated by one single migration from Asia as opposed to several waves.

The land bridge connecting New Guinea and Australia became submerged approximately eight thousand years ago, thus isolating the populations of the two landmasses.

The small population of moderns had spread from the Near East to South Asia by fifty thousand years ago, and on to Australia by forty thousand years ago, Homo sapiens for the first time colonizing territory never reached by Homo erectus.

It has been estimated that from a population of two thousand to five thousand individuals in Africa, only a small group, possibly as few as one hundred and fifty to one thousand people, crossed the Red Sea.

Of all the lineages present in Africa only the female descendants of one lineage, mtDNA haplogroup L3, are found outside Africa.

Had there been several migrations one would expect descendants of more than one lineage to be found outside Africa.

L3's female descendants, the M and N haplogroup lineages, are found in very low frequencies in Africa (although haplogroup M1 is very ancient and diversified in North and Northeast Africa) and appear to be recent arrivals.

A possible explanation is that these mutations occurred in East Africa shortly before the exodus and, by the founder effect, became the dominant haplogroups after the exodus from Africa.

Alternatively, the mutations may have arisen shortly after the exodus from Africa.

Some genetic evidence points to migrations out of Africa along two routes.

However, other studies suggest that only a few people left Africa in a single migration that went on to populate the rest of the world, based in the fact that only descents of L3 are found outside Africa.

From that settlement, some others point to the possibility of several waves of expansion.

Migrants from Central Asia and the Middle East are believed to have colonized Europe, moving northwestward over time.

By the time anatomically modern humans first enter Europe, Neanderthals are already well-established in the region. The question of whether these two populations interbred remains a subject of ongoing debate.

Evidence suggests that modern humans and Neanderthals coexisted in various regions, including the Iberian Peninsula and the Middle East, where interbreeding may have contributed Neanderthal genes to early Paleolithic Europeans and, ultimately, to modern European populations.

Regardless of whether interbreeding occurred, it is generally believed that early human populations took refuge in hypothetical Ice Age shelters, later repopulating Europe as the glaciers receded—forming the ancestral foundation of present-day European populations.

An alternative theory proposes that modern Europeans primarily descend from Neolithic populations originating in the Middle East, whose migrations into Europe are well documented.

The debate over the origins of Europeans has often been framed as a question of cultural diffusion versus demic diffusion.

Both archaeological and genetic evidence strongly support demic diffusion—the idea that a population spread from the Middle East over the last 12,000 years, gradually replacing or assimilating earlier groups.

However, some researchers have challenged this view using the genetic concept of Time to Most Recent Common Ancestor (TMRCA). This approach has been used to argue in favor of cultural diffusion, suggesting that technological and cultural advancements spread without significant population movement.

The debate remains ongoing, with scholars examining the complex interplay between migration, gene flow, and cultural exchange in shaping Europe's early populations.

Modern human culture begins to evolve at an accelerated pace, marking a significant shift in behavior and innovation.

Some anthropologists, notably Jared Diamond, author of The Third Chimpanzee, describe this period as a "Great Leap Forward." During this time, modern humans adopt new cultural and technological practices, including:

• Burying their dead, often with grave goods, suggesting ritual or symbolic thought,
• Crafting clothing from hides, improving survival in colder climates,
• Developing advanced hunting techniques, such as trapping pits or driving animals off cliffs, and
• Creating cave paintings and other forms of artistic expression.

As human culture advances, different populations begin to introduce novelty into existing technologies. Unlike earlier hominins, modern humans show regional variations in artifacts such as fish hooks, buttons, and bone needles, demonstrating a previously unseen diversity of tools and personal items.

Anthropologists identify several key markers of modern human behavior, including:

• Tool specialization,
• Adornment with jewelry and symbolic imagery (such as cave drawings),
• Organized living spaces,
• Elaborate rituals, including burials with grave gifts,
• Exploration of harsh or previously uninhabited environments, and
• The development of barter trade networks.

Debate continues over whether these advancements were the result of a sudden cognitive "revolution"—sometimes called "the big bang of human consciousness"—or whether they emerged through a more gradual evolutionary process.

The development of stone tools appears to have progressed in gradual steps until around 50,000 to 40,000 years ago.

Each successive Homo species—from H. habilis to H. ergaster to H. neanderthalensis—began at a higher technological level than its predecessor. However, once a phase began, further innovation remained slow, reflecting a culturally conservative approach to tool-making.

Around 50,000 BP, however, modern human culture began to evolve at a significantly faster pace. While Neanderthal populations typically displayed little variation in their tool-making techniques, the Cro-Magnon immigrants introduced increasingly refined and specialized flint tools, such as knives, blades, and skimmers.

Additionally, Cro-Magnons expanded beyond stone, pioneering the use of bone tools, marking a major advancement in prehistoric technology.