The Mammoth Steppe was the world's largest biome 25,000 years ago. It was similar to the African savannah. The African savanna, filled with herbivores and the predators that prey on them, such as crocodiles, lions, wild dogs, is rich with unique flora and fauna.
Like the savannah, the Mammoth Steppe was dry and had expansive grasslands. The biome was quite cold, and the vast expanse spread from Spain to Siberia across the Bering into Alaska and parts of Canada. Canada at the time was an ice sheet not conducive to biodiversity.
The steppe includes large herbivores such as horses, musk ox, bison, wooly rhinoceros, and the rare Mammoth. Wolves, wolverines, bears, and small pockets of humans were the primary carnivores.
Due to warming, the steppe changed from dry to moist, ringing in a new environment of moist soils that favored trees, bushes, and moss. Snow and ice covered the region in winter, and the albedo (white reflects the Sun's light to space) delayed spring. The invasive vegetation was able to thrive despite the large numbers of animals. Still, it was too much growth for their hooves to flatten and kill trees and bushes and herbivore populations plummeted as a result of a likely assist from humans along with other factors.
We are seeing this invasive process play out again today in the thawing soils of the tundra from the North Slope of Alaska to Siberia. It is called Shrubification. It reduces albedo and damages the tundra with shrubs that weaken the permafrost by roots that break the soil apart, allowing more heat to degrade further, a system that stores methane and CO2 locked under the ice. The thawing adds more moisture which provides water for the plants to extend their range, releasing and adding even more deadly greenhouse gases from the permafrost that is, unfortunately, a current active climate tipping point that threatens our survival along with the rest of the world's biodiversity.
Speaking of abrupt climate change, the Younger Dryas period (transition from the last glacial period into the present interglacial) did not kill off the Mammoth, though it likely reduced their population. NOAA writes on that climate change timeframe:
About 14,500 years ago, Earth’s climate began to shift from a cold glacial world to a warmer interglacial state. Partway through this transition, temperatures in the Northern Hemisphere suddenly returned to near-glacial conditions. This near-glacial period is called the Younger Dryas, named after a flower (Dryas octopetala) that grows in cold conditions and that became common in Europe during this time. The end of the Younger Dryas, about 11,500 years ago, was particularly abrupt. In Greenland, temperatures rose 10°C (18°F) in a decade (Alley 2000). Other proxy records, including varved lake sediments in Europe, also display these abrupt shifts (Brauer et al. 2008)
The scenario that early humans killed the Mammoth by overhunting and stampeding them over cliffs has taken a hit with new research that humans lived with them harmoniously, and the last Mammoths, isolated in pockets conducive to their survival, did not go extinct until 4,000 years ago.
According to a new study published in the journal Nature, reviewed by the AGU, and published in Eos Magazine, DNA samples from all over the Arctic were used to create a 50,000-year history of the Mammoth Steppe. The findings found that it was indeed climate change that caused the extinction of the Mammoth and the extinction of the mega-fauna of the Pleistocene.
Scientist Elise Cutts writes:
This effort was made possible by a massive new data set of 1,541 new plant genomes, which allowed the researchers to identify significantly more eDNA than they previously could have, said Arctic botanist and study coauthor Inger Greve Alsos of the Arctic University of Norway.
Along with these eDNA data, the researchers used a computational model of the past biome’s climate and the distribution of prehistoric humans across the Arctic. Together the model and the eDNA data revealed how animal and plant populations shifted as humans moved north and the globe thawed going into the Holocene. The analysis showed that vegetation across the Arctic shifted as the climate changed.
“When the climate becomes warmer in the Holocene, the vegetation in different regions starts to become different,” said paleoecologist Yucheng Wang of the University of Cambridge and University of Copenhagen, the study’s lead author. “For example, in the North Atlantic…we see aquatic plants increase dramatically immediately after the warming, while in central Siberia, which is more continental, we see that the steppe vegetation maintained basically unchanged.”
The eDNA from herbivores like mammoths tended to be absent from samples with more eDNA from woody plants and aquatic plants and from samples that the climate model associated with greater and more seasonally intense precipitation. This finding could indicate that the wetter Holocene climate allowed marshes, lakes, and forest to encroach on steppe vegetation, leaving large herbivores like mammoths without a suitable habitat. This interpretation placed the new results on one side of a long scientific debate on the nature of the mammoth steppe and the cause of the megafauna extinctions.
An alternative theory is that the mammoth steppe disintegrated because humans overhunted the large herbivores—what researchers sometimes call the human overkill scenario. The new data, however, didn’t show much evidence for overkill. Unlike vegetation and precipitation, the presence of ancient humans was almost completely unrelated to the eDNA-based distribution of most herbivores—including mammoths—across the Arctic. What’s more, the researchers found that mammoths survived in parts of Siberia until as recently as 4,000 years ago. Not only was this longer than previously thought, but the finding also suggested that humans coexisted with megafauna for thousands of years without overhunting them.
Although the debate about the fate of the mammoth steppe and the definitive cause of megafauna’s extinction is not over, this research “definitely added some very robust evidence into this debate to support that climate change was the driver for the last late Quaternary extinction,” Wang said.
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