In prehistoric times, the climate was much warmer, and carbon dioxide levels were over four times higher than today.
This produced abundant plant life, and also increased oxygen levels, meaning animals grew and evolved to be much larger than those found today — at least that is what scientists believe.
Ancient humans would have been tasked with hunting and running from such massive animals like the Wooly Mammoth, huge hyenas, not to mention crocodiles of gargantuan proportions.
None were these animals bigger than in the Americas, a place that had remained cut off from the rest of the world, allowing prey and predators to grow without outside interference.
When humans first arrived on the continent, they would have encountered not only animals they had never seen before both those of a size completely foreign to them.
Many theories exist over who the first humans to reach the Americas really were, including the Soultrean hypothesis, which claims that prehistoric Spaniards arrived there first.
A controversial theory, it points to evidence of distinctive Soultrean tools found in North America which provided the basis for later Clovis technology that spread throughout the region.
Proponents say that the people of the Solutrean culture some 21,000 to 17,000 years ago migrated to North America by boat along the pack ice of the North Atlantic Ocean.
Shrouded in controversy and dismissed by many, their research was put into practice during the Smithsonian Channel’s documentary, ‘Ice Bridge: The Impossible Journey’.
According to the theory, they landed at Chesapeake Bay, the stretch of watershed that runs around 524 miles from Cooperstown, New York, to Norfolk, Virginia.
Their first task, the documentary’s narrator noted, was to “make the tools and weapons on which their survival depends” for fear of the unknown.
That unknown was limitless, with the great canopy of icy wilderness containing flora and fauna never before encountered by the Solutreans, North America at the time home to “massive prehistoric mammals unlike any in Ice Age Europe”.
The narrator continued: “Among them, one of the most terrifying predators of all time, the short-faced bear.
“Capable of chasing its prey at 25mph and reaching up to heights of 13 feet.”
The short-faced bear reached its peak population somewhere around 800,000 years ago, and became extinct 11,000 years ago, around the same time the city of Jericho in the West Bank was emerging, and when Britain was still inhabited by hunter gatherers.
There are two recognised species: the lesser short-faced bear (Arctodus pristinus) and the giant short-faced bear (Arctodus simus), with the latter believed to be the largest known terrestrial mammalian carnivores that has ever existed.
They would have also faced giant ground sloths, known by their name of Megalonyx jeffersonii. The largest of the species, they reached the size of an ox when fully grown, around 3 metres in length, and weighed up to 1,000kg.
Evolving in South America around 35 million years ago, the giant ground sloth eventually migrated to North America around eight million years ago.
It would have lived alongside the short-faced bear, mostly around rivers and lakes, and existed in a time known as the “Great Ice Age”.
At this time, during its peak, as much as 30 percent of the Earth’s surface was covered by glaciers, with parts of the northern oceans frozen, leaving an environment in which only the hardiest of animals could survive.
In 2018, archaeologists discovered the fossilised footprints of ancient humans at White Sands National Monument in New Mexico.
The same site turned up human footprints in the footprints of giant ground sloths, suggesting to scientists that humans may have once hunted the beasts.
While the Solutrean hypothesis is held up in some circles, other experts say it is “scientifically implausible”, like geneticist Dr Jennifer Raff.
Writing in The Guardian in 2018, she said the theory “suggests a European origin for the peoples who made the Clovis tools, the first recognised stone tool tradition in the Americas”.
Dr Raff, who appeared in the Smithsonian documentary, added: “In addition to the scientific problems with the Solutrean hypothesis which I’ll discuss shortly, it’s important to note that it has overt political and cultural implications in denying that Native Americans are the only indigenous peoples of the continents.”
