Everything Everywhere Daily: History, Science, Geography & More - Ice Ages

Episode Date: April 20, 2022

Subscribe to the podcast!  https://podfollow.com/everythingeverywhere/ Record your family's memories at https://StoryWorth.com/Everything -------------------------------- Five different times during the Earth’s history, the planet has entered a prolonged period of reduced temperatures. When this happens, massive ice sheets form, and sea levels drop.  While some of these events occurred billions of years ago, not all of them were in the distant past.  In fact, the last such event had a profound impact on the development of humans as a species. Learn more about ice ages, how they affect the planet and how they affect humanity, on this episode of Everything Everywhere Daily. -------------------------------- Associate Producers: Peter Bennett & Thor Thomsen   Become a supporter on Patreon: https://www.patreon.com/everythingeverywhere Update your podcast app at newpodcastapps.com Discord Server: https://discord.gg/UkRUJFh Instagram: https://www.instagram.com/everythingeverywhere/ Twitter: https://twitter.com/everywheretrip Website: https://everything-everywhere.com/everything-everywhere-daily-podcast/ Everything Everywhere is an Airwave Media podcast." or "Everything Everywhere is part of the Airwave Media podcast network Please contact [e-mail] to advertise on Everything Everywhere. Learn more about your ad choices. Visit megaphone.fm/adchoices

Five different times during the Earth's history, the planet has entered a prolonged period of reduced temperatures. When this happens, massive ice sheets form and sea levels drop. While some of these events occurred billions of years ago, not all of them were in the distant past. In fact, the last such event had a profound impact on the development of humans as a species. Learn more about ice ages, how they affect the planet, and how they affect humanity, on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed.

It effectively turned day into night. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. Let's start out this discussion of ice ages with what an ice age is. An ice age is nothing more than a prolonged period of time of reduced temperatures such that large continental size ice sheets and glaciers will form. These periods do not last decades, centuries, or even millennia. Ice ages are periods that are millions of years long. Much of the confusion comes about from the colloquial use of the term the Ice Age, which is usually in reference to the most recent glaciation,

which I'm going to get to in a bit. According to geologists, there have been at least five ice ages in the history of the earth. The earliest would be the Pangolan glaciation, which occurred about 2.9 to 2.7 billion years ago. This is often not included on the list of ice ages because it occurred so long ago, and the evidence for it is the shakiest. This is why I said there were at least five ice ages.

What is usually considered to be the first ice age was the Huronian glaciation, which was around 2.4 to 2.1 billion years ago. The next was the cryogen ice age. This occurred about 850 to 635 million years ago. This was still

before the Cambrian explosion, which saw the rapid rise of multicellular life. One or both of these early ice ages may have been a period known as Snowball Earth. The Snowball Earth hypothesis holds that at some point in the distant history of Earth, the entire planet, or at least most of it, down to the tropical latitudes, was covered in ice. The planet wouldn't have been blue or green, but rather white, from all the frozen seas. The evidence suggesting that there was a snowball Earth comes from the existence of glacial sediment at what was then tropical latitude. The Snowball Earth hypothesis is far from agreed upon amongst geologists, and evidence from that

far back is always difficult to interpret. Most of the difficulty comes from determining what the paleo latitudes were for different periods. Due to play tectonics, the Earth's land masses are slowly roaming around the planet over the course of tens and hundreds of billions of years. We can use paleomagnetic evidence to determine what the latitudes were when the rock was formed, but when you go back that far, there's much we don't know about the Earth's magnetosphere from that time. If true, the Snowball Earth Hypothesis might have profound implications for the development of early life on Earth. It could have been a shock to the planet, which drove the evolution of

bacteria, which had to adapt to survive. The next Ice Age was the Andean Saharan Ice Age, which occurred from 450 to 420 million years ago. It's named after the glacial evidence, which has been found in South America and Northern Africa. This was also one of the first major extinction events on Earth, which was when animals such as trilobites went extinct. The ice age after that was the Karu Ice Age, which went from 360 to 289 million years ago. Plant life was rampant on Earth during this period, which took much of the carbon dioxide out of the atmosphere and reduced the ability of the atmosphere to retain heat. After the Karu Ice Age, there was a long period of almost 300 million years where there were

no ice ages at all. The last and most recent Ice Age is the Quaternary, which began 2.58,000, million years ago. And technically speaking, we are still in the middle of an ice age right now. Before I mentioned that there was some confusion about the term ice age, and this is where the confusion comes from. Ice ages are not monolithic periods where there was ice and cold and nothing else. There are periods within each ice age known as glaciation's and interglacial periods. The ice caps will ebb and flow back and forth over periods of tens of thousands of years or longer. So within the Ice Age that we are currently living in, we are currently in an interglacial period,

which is the period between massive ice sheets. The last glacial period was known as the Wisconsin Glacial episode, and it ended about 11,000 years ago. When you hear people talking about the Ice Age, this is almost always what they're talking about, the most geologically recent period where massive ice sheets covered much of North America and Europe. During the last 2.5 million years at the Quaternary Ice Age has been taking place, the period between glaciation has been about 40,000 to 100,000 years. The Wisconsin glaciation started about 75,000 years ago and reached its maximum about 22,000 years ago. I'm going to spend the rest of the episode talking about the Wisconsin glaciation because

that's what we know the most about given how recently it ended. But before I do that, I should address the big question of why Ice Age's happen. As far as we can tell, there is no one single cause of ice ages. They can be caused by a combination of plate tectonics, changes to the atmosphere, as well as Milankovic cycles, which I previously did an episode on, and they're the various cycles of the Earth's orbit and tilt which can augment or nullify each other. This is an area of research where there is still a lot of debate. The Milankovic cycles don't perfectly fit to the glaciation cycles of the last 2.5 million years. This is known as the 100,000-year problem, and there are numerous theories that try to explain the discrepancy.

For a glacier to form, all you need is for the rate of snow accumulation to be greater than the rate of melting. If more snow can be deposited in the winter, then can be removed in the summer, you will see the gradual formation of glaciers. So what exactly happened during the last glaciation? What was the Earth life back then? For starters, the massive ice sheet on the northern hemisphere wasn't uniform. Many people think of it as a semicircular cap that would just sit on the top of the earth. The ice sheet was actually very uneven in what it covered. Most of Canada, the Midwestern United States, New England, Scandinavia, Northern Europe, all the way through Siberia, was covered in ice.

However, the northern part of Asia was not covered in ice, and this would include the far eastern parts of modern Russia. Likewise, most of Alaska was not covered in ice as well. The furthest extent south the ice extended in North America was about the middle of Illinois, Indiana, and Ohio. The ice didn't get down as far in Europe. However, the northern parts of the island of Great Britain would have been covered in ice. The only real glaciation in the southern hemisphere would have been in Antarctica, which is still covered in ice, and many more glaciers in the Andes Mountains in South America. The ice sheets during the last glaciation would have been incredibly thick. The average thickness would have been about 4,000 meters or 2.5 miles of ice.

And this is not a par with the thickness of ice in Antarctica today. Thousands of meters of ice weighs a lot, and all of that ice impacted the land underneath it. The mass of the ice literally deformed the land below it. When the ice retreated, all that land which was pushed down by the ice began springing back up. This is called isostatic rebound. This process is still ongoing in many parts of the world today. There are some parts of the world where the land is rising as fast as one centimeter a year. The country of Finland is actually growing by seven square kilometers a year due to isotastic rebound.

And the Gulf of Bothnia, which sits between Sweden and Finland, is eventually going to totally disappear due to the uplift of the land underneath it. Likewise, many of the lakes in Canada, Minnesota, and Wisconsin will also disappear at some point as the land rises and all of the water slowly drains away. It is estimated that the post-glacial rebound of the land will probably last another 10,000 years. If you could have looked at a map of the Earth during the glacial maximum about 22,000 years ago,

it would have looked radically different. All of the water which made up the ice and the ice sheets had to come from somewhere. And the result was dramatically lower sea levels than what we have today. During the glacial maximum, the sea levels would have been 125 meters or 410 feet below what the sea level is today.

That means that much of Indonesia and the Philippines would have been connected by land to the rest of Asia. Australia would have been connected to Pua New Guinea. All of the islands in Japan would have been connected to each other, and southern Japan would have also been connected to Asia. The British islands would have all been connected to Europe with a huge grassy plain between them in Norway. Most importantly, Alaska would have been connected to Siberia

by what is known as the Bering Land Bridge. This was the most probable route that the first humans probably took to the Western Hemisphere. Many people envisioned the first people crossing the Bering Land Bridge as walking over a glacier while wearing animal skins. Most likely, it was a grassy plain, and they just chased game into the area and kept on going. They weren't necessarily looking for a new home. The movement across the land bridge wasn't one way. It's also believed that horses originally migrated to Asia from North America. The last glaciation began to retreat about 19,000 years ago,

and there was a small reverse in the warming of the planet from 12.9,000 years ago to 11.7,000 years ago. This period was known as the Younger Dryas, and it seems to play a very important role in the development of modern humans. Many of the first signs of human civilization that we see, such as Golbeki-Tepi, appear about the same time. One theory for the sudden reversal in temperatures might have been a comet or meteor that impacts, in North America on the ice sheet. But I will leave that story for another day. Ice ages have played an important part in the history of the earth and the development of life.

The most recent Ice Age, the one that we're probably still in the middle of, played a major role in the development of modern humanity. And even though the massive ice sheets have been gone for over 10,000 years, they are still shaping the world that we live in today. Everything Everywhere Daily is an Airwave Media podcast. The associate producers are Thorpe Thompson and Peter Bennett. Today's review comes from listener C-style over at Podchaser. They write,

Great podcast that covers a new topic in medium detail every day. Some days, the topic will be related to the prior episode, while other days it will be something totally random, but still interesting. Love the podcast. My only feedback is I don't think you need to mention, this will be covered in a future episode as often. I think most of your listeners realize this.

Perhaps just say this once a week or two. Either way, keep up the good work. Well, thanks, C-style. One of the reasons why I say something will be in a future episode is that it can show the process of how one show can lead to another show. One of the most frequent questions I get is how I come up with ideas for episodes. Many, if not most of my ideas, come from researching past shows. One idea can spawn multiple more. For example, I can think of about five different episodes which relate to this episode's Ice Age topic, and those five might lead to even more.

All of those get put into the great master list of show ideas, which currently has, 734 ideas listed. Remember, if you leave a review over at Podchaser until the end of April, they will make a donation to help feed Ukrainian refugees, which will be matched by several other podcast companies.