In my last two videos I've talked about ice ages and how they've affected our planet and its geography. Leaving last but not least the natural environment. So without further ado.
Here's the biogeography of the last ice age. The trick to understanding the Earth at this time is to understand this graph. I showed it briefly in the first video in the series but didn't really explain it.
Here we can see the Air's capacity for moisture in relation to temperature, the higher the temperature the more water can be held by the atmosphere, think of a place in the tropics warm and humid. Therefore the lower the temperature the drier the atmosphere becomes meaning the last glacial maximum, the coldest time in recent history, would have also been the driest period for the planet as well. That's why the major trend we'll see across the world was the expansion of tundra and deserts.
Now this might sound strange at first first, but Tundra may actually be the coolest biome I get to talk about today you see in modern times tundra is restricted to the rocky arid glacier torn scraps of land around the Arctic Denying the biome the proper amount of sunlight to support any substantial plant growth. The result of which being a largely desolate habitat only barely more productive than a desert thanks to all the resilient mosses that manage to grow here. During the Ice Age however, the permafrost biome reached far beyond the Arctic, covering most of what remains of Europe extending far into the Asian interior all the way to the Russian East Coast.
This position closer to the equator granted the tundra a greater solar irradiance or in other words it received enough solar energy to support the growth of grasses, herbs and shrubs. What was created was an absolutely humongous tract of land perfectly suited to the feeding habits of grazing animals. This is how the tundra of this time earned its other name the mammoth steppe.
But it wasn't just mammoths that thrived under these conditions, but rather a huge ecosystem analogous to the African savannah was able to develop, if it were still around today. You could literally go on a safari across these wide-open plains and see essentially the same exact animals. You'd expect on an African safari except even bigger.
Instead of zebras there were horses, instead of wildebeests there were musk ox, instead of the african buffalo there were bison, instead of the rhinoceros there was the woolly rhinoceros and yes instead of elephants, there were mammoths. Together this made the mammoth step a surprisingly productive environment, made all the more intriguing by the fact that there are no modern equivalents besides a few isolated pockets within the Altai and Sayan mountains. Looking at images of these places today it becomes easier to imagine how a landscape like this could have supported such a large community of flora and fauna.
But where the permafrost dwindled, the mammoth steppe gave way to another even more encompassing biome- deserts. While separated by thousands of miles deserts all have one thing in common- minimal plant and animal life, and considering this is the biogeography of the Ice Age that means there isn't all that much to talk about here. Huge polar deserts encapsulated the extreme latitudes of North America and Eurasia Forming perhaps the least hospitable environment on the planet.
Leaving the high latitudes behind the eurasian polar desert transitioned into a temperate desert from what's now parts of Kazakhstan through China and Mongolia. While still, you know, a desert, temperate deserts are still capable of harboring delicate communities. On account of the fact that what little moisture does make it here comes in liquid form.
But don't get any ideas as the Himalayas just a little further south created a massive Alpine desert across the Tibetan Plateau. Reducing the bioproductivity here back down to levels similar to the polar deserts. Now despite the Earth being in a quote-unquote Ice Age, global temperatures realistically only dropped between five to ten degrees Celsius lower than today.
So while this had huge implications for the mid and high latitudes the Earth's equatorial regions remained relatively unchanged in terms of temperature. Which is why continuing yet even further south will find the big one, extreme tropical deserts. Everybody's favorite the Sahara and Arabian deserts were fully intact and considering the Red Sea was just a lake at this time it becomes a little clearer that these two deserts are in fact a single desert that just so happens to be divided by a body of water.
Crossing over to the southern hemisphere we can see that Australia or I guess I should say Sahul, also featured a desert comparable to the one found here today. Nothing new to really see here. The same can be said for Africa's Kalahari and Namib Desert more or less resembling their current form.
What did I say, The mammoth steppe really was way more interesting than this. South America at the very least saw the formation of a new desert spanning its interior, covering essentially all of modern Argentina through Paraguay and deep into Bolivia. Across land that, in modern times, hosts a portion of the Amazon rainforest.
In these times however the Amazon had contracted into at least two separate domains and likely was even more fragmented than this. A third large forest was to be found in the middle of what's now Brazil. This however was not a tropical rainforest but rather a temperate broadleaf forest, more similar to those found in places like the eastern United States and Europe today.
Together these sparse forests served as a refuge area for many animals and plant species displaced by the changing climate. Eventually when the earth warmed back up it was from these refuge' that the animals and plants alike marched outwards from to reclaim the larger Amazon basin. Helping to explain why these portions of the modern-day Amazon are more biodiverse than what has since regrown and really more biodiverse than anywhere else on the planet actually.
Between the forests and deserts a number of ecoclines or transitional environments composed a buffer between the two extremes. For the most part taking the form of large grasslands and savannas. Now this doesn't exactly relate to the ice age, but around 2.
7 million years ago or roughly the same time this whole quaternary glaciation began, the Panama Isthmus rose up from beneath the ocean to connect North and South America together. Prior to this South America had existed as an isolated island continent ever since it broke apart from Africa someone hundred and 40 million years ago. The further the two continents drifted apart the more isolated their flora and fauna became, by 50 million years ago Africa had already joined with Asia, but South America still had 47 million years to go.
During this period of isolation the species of the continent had time to evolve in some pretty unique ways. North America on the other hand was still periodically connected to Greater Eurasia and by extension even Africa, and as a result hosted a pretty similar species makeup to these areas perhaps with just a little added North American flavor. So when these two continental bodies finally merged what's known as the Great American Interchange began, allowing for the melding of two entirely different biogeographic realms.
Bby the time of the most recent Ice Age this exchange had already been underway for nearly 3 million years aided by the extension of the remainder of the Central American rainforest. The North American continent as a whole however, did pretty well for itself in terms of environment. Beyond the small deserts to be expected surrounding the glaciers two notable forests were to be found on either coast with all kinds of different Transitional grasslands in between them as well as some alpine tundra deep in the Rockies, but that's really little different from today.
The biggest difference here, like I said in the last video, is that this was one of the few places that actually received more rainfall back then than it does now. Hence Lake Bonneville and Lahontan. So while occupied by deciduous forests today, 20,000 years ago the east coast of North America was home to some of the only taiga forest on the planet, making much of what's now the United States ironically look more like Russian Siberia.
As the glaciers receded this forest would follow the ice northward into Canada and eventually wrap around the entire northern hemisphere. Displacing the mammoth steppe to become the largest biome on the planet today. Over on the west coast we'll find another thin strip of forest-steppe clinging to what's now the states of Washington, Oregon and California.
It's here that the giant redwood trees have been continuously growing for over 200 million years, meaning this area likely would have looked more are less similar to what it does now. While individual redwoods can live over 2,000 years through their own form of asexual reproduction, the exact genes of trees can last upwards of thirty thousand years meaning there are likely clones of redwood trees still alive today that were also alive during and even before the last glacial maximum. Which I don't know about you but that's just crazy to me.
Moving over to Africa we can see the basic layout of the continent remained the same with one, two, three major deserts and some green in the middle, as well as what can really only be described as a small Fez of semi-desert across what's modern Morocco, Algeria and Tunisia. The big difference here though, is that forests have almost completely disappeared from the continent in this time, save for a handful of lasting reserves along the Congo River and Western Guinean post. These however are dwarfed by the Congo rainforest of today.
Without as large of a forest refuge as the Amazon the African rainforest were likely less capable of preserving species which could explain why the Congo rainforest is the least biodiverse of the three major rainforests today. A greater collection of forests at the time could actually be found further north across the European-Mediterranean region. Caught between the steppe tundra of the north and the tropical desert of the south this also likely would not have been a continuous forest, but rather large patches interspersed with steppe.
Following this vegetation eastward eventually this forest steppe dried out into a semidesert, stretching across the mountains of the Middle East all the way to India. This region still received yearly monsoon rains. Leaving eastern India and either side of the Sundaland covered in tropical rainforest.
This Sunda rainforest would have been the largest forest in the world at the time and actually if it weren't for humans would have remained the largest forest in modern times. Cutting between the forests was a corridor of savanna where monsoon rains couldn't quite reach and it was this shifting corridor that human migrants moved through, starting in the steppe forests of Taiwan and coming to populate all of Australasia, all the way to Sahul. Here while the speech is changed with the crossing of the Wallace Line the rainforest biome nevertheless continued through what's now the island of New Guinea.
While what was most of Australia only received enough moisture to sustain woodlands and savanna before giving away to desert in the interior, similar to South America. Sahul's position as an island continent meant that the plants and animals here went down a much more specific evolutionary path than those found across the greater connected landmasses of Africa, Eurasia and North America. If you're noticing a trend in the animals I've mentioned it's not a coincidence literally every habitable continent, sorry Antarctica, featured diverse communities of megafauna or giant animals.
Likely a result of the colder temperatures selecting for greater body masses. The world at this time was dominated by grazing and browsing herbivores that would put the giants of our time to shame. Of course that's the second thing all of these Ice Age animals have in common.
They're all also extinct now. There isn't actually a full consensus within the scientific community as to the causes of this quaternary extinction event, but I'm going to let you guess the primary suspect I'll even give you a hint: nearly all of these extinctions coincide with the expansion of another animal species moving across the grasslands of the world. Yep.
That's right humans When looking at the realms that were hit hardest by this wave of megafauna extinction an interesting trend emerges. South America lost 54% of its megafauna by 4000 years ago, North America lost 66%, Australasia lost 67% while Eurasia only lost 23%, Indomalaya 8. 2% and Africa only lost 5.
1%. What we can see here is that the rate of extinction increases the further away from Africa we look. The hypothesis here being that those large megafauna native to Africa evolved alongside early humans allowing them to adapt and develop strategies or behaviors to avoid overpredation, As humans expanded outwards from here however, none of the megafauna outside had any clue what a human was or how to cope with us.
Together this helps to explain why today Africa harbors more large mammals than anywhere else in the world. As it turns out an instinctual fear of humans may have been the most advantageous trait for animals to develop. In the end learning about the biogeography of the ice age helps reveal to us the destructive nature of unimpeded human progress while showing us just how nature was doing right before the planet was met with its most destructive species by far.
Hey everyone, I hope you've enjoyed this trilogy of ice age videos. To me this was one of the most fascinating times not only in human history but the Earth's history as a whole. If you'd like to keep seeing videos like these you can check out my patreon to help support what I do.
But of course in times like these don't worry if that's not possible.
