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Although it may be difficult to understand, our planet is constantly changing. Continents are constantly shifting and colliding with each other. Volcanoes erupt, glaciers expand and retreat, and life must keep up with all these changes that occur.

Throughout its existence, at various periods that lasted millions of years, the Earth was covered by a kilometer-long polar ice sheet and mountain glaciers. The topic of this list will be ice ages, characterized by very cold climates and ice extending as far as the eye can see.

What is an ice age?
Believe it or not, the definition of an ice age is not as clear-cut as some may think. Of course, we can characterize it as a period when global temperatures were much lower than today, and when both hemispheres were covered with a layer of ice extending thousands of miles towards the equator.

However, the problem with this definition is that it describes any ice age from today's perspective and does not actually take into account the entirety of planetary history. Who is to say that today we are not living in colder than average temperatures? In this case, we are actually in an ice age right now. Only a few scientists who have devoted their lives to studying such phenomena can confirm this. Yes, we are actually living in an ice age, as we'll see in a minute.

A better definition of an ice age would be that it is a long period of time when the planet's atmosphere and surface are cold, resulting in the presence of polar ice sheets and mountain glaciers. This can last for several million years, during which there are also periods of glaciation, characterized by ice cover and the growth of glaciers on the planet's surface, as well as interglacial periods - intervals lasting several thousand years when the ice retreats and becomes warmer. In other words, what we know as the "last ice age" is essentially one such stage of glaciation, part of the larger Pleistocene ice age, and we are currently in an interglacial period known as the Holocene, which began around 11,700 years ago.

What causes an ice age?
At first glance, the ice age looks like some kind of global warming in the opposite direction. This is true to a certain extent, but there are several other factors that can initiate and contribute to the onset of an ice age. It is important to note that the study of ice ages has only recently begun, and our understanding of the process is not yet complete. However, there is some scientific consensus on several factors that contribute to the onset of the Ice Age.

One such obvious factor is the level of greenhouse gases in the atmosphere. There is evidence that the concentration of these gases in the air rises and falls as ice sheets retreat and grow. But some argue that these gases do not necessarily trigger every ice age and only influence its severity.

Another key factor that plays an important role is tectonic plates. Geological records indicate a correlation between the position of the continents and the onset of the Ice Age. This means that in certain positions the continents can impede the so-called Global Ocean Conveyor - a global system of currents that transport cold water from the poles to the equator and vice versa.

Continents could also sit right on top of the poles, like Antarctica today, or result in polar bodies of water being completely or partially landlocked, like the Arctic Ocean. Both of these factors contribute to ice formation. Continents can also gather around the equator, blocking ocean currents, leading to an ice age.

This is exactly what happened during the Cryogenic Period, when the supercontinent Rodinia covered most of the equator. Some experts even say that the Himalayas played an important role in the current ice age. Once these mountains began to form about 70 million years ago, they contributed to increased precipitation on the planet, which in turn led to a steady decline in CO2 in the air.

Finally, we have the orbits in which the Earth moves. This also partially explains the glacial periods and interglacial periods during any given ice age. The Earth experiences a series of periodic changes during its orbit around the Sun, which are called Milankovitch Cycles. The first of these cycles is the Earth's eccentricity, which is characterized by the shape of our planet's orbit around the Sun.

Every 100,000 years or so, the Earth's orbit becomes more or less elliptical, meaning it will receive more or less sunlight. The second of these cycles is the tilt of the planet's axis, which on average changes by a few degrees every 41,000 years. This tilt affects Earth's seasons and the difference in solar radiation received by the poles and the equator. Third, we have the precession of the Earth, which is the wobble as the Earth rotates on its axis. This occurs approximately every 23,000 years and causes winter in the Northern Hemisphere to occur when the Earth is farthest from the Sun, and summer when it is closest to the Sun. If this occurs, the difference in severity between seasons will be greater than today. Apart from these basic factors, we can also sometimes suffer from a lack of sunspots, large meteorite impacts, massive volcanic eruptions or nuclear wars, which could potentially lead to the onset of an ice age, among other things.

Why do they last so long?
We know that ice ages usually last millions of years. The reason for this can be explained using a phenomenon known as albedo. This is the reflectivity of the Earth's surface when it comes to short-wave radiation from the Sun. In other words, the more of our planet's surface is covered with white ice and snow, the more solar radiation is reflected back into space, and the colder it gets on Earth. This leads to even more ice and even more reflectivity in a positive feedback cycle that lasts millions of years. This is one of the reasons why it is so important that Greenland's ice stays where it is. Because if this doesn't happen, the island's reflectivity will decrease, causing global temperatures to rise.

However, ice ages eventually end, as do their glacial periods. As the air gets colder, it can no longer hold as much moisture as before, which in turn means less snow falls and the ice caps cannot expand or even maintain them. The result is a negative feedback cycle that marks the beginning of an interglacial period.

Following this logic, a theory was proposed in 1956 suggesting that an ice-free Arctic Ocean would cause more snowfall at higher latitudes, above and below the Arctic Circle. There may be so much of this snow that it does not melt during the summer months, increasing the Earth's albedo and decreasing overall temperatures. Over time, this will allow ice to form at lower latitudes and in the mid-latitudes - a push that starts the glaciation process.

But how do we know that there really was an ice age?
The reason people started thinking about ice ages in the first place was because of some huge boulders that ended up in the middle of an empty area with no explanation as to how they got there. The study of glaciation began in the mid-18th century, when Swiss engineer and geographer Pierre Martel began documenting the scattered rock formations within an Alpine valley and below a glacier. Locals told him that these huge boulders were pushed by a glacier that once extended much further up the mountain.

Over the decades, other similar cases were documented around the world, becoming the basis for the theory of ice ages. Since then, other forms of evidence have been taken into account. Geological features including the previously mentioned rocks containing glacial deposits, carved valleys such as fjords, glacial lakes, and various other forms of rugged land surface. The problem with them is that they are difficult to date, and subsequent glaciations can distort or even completely erase previous geological formations.

More accurate data comes from paleontology - the study of fossils. Although not without some flaws and inaccuracies, paleontology tells the story of the Ice Ages by showing us the distribution of cold-adapted organisms that once lived at lower latitudes, and organisms that typically thrive in warmer climates that have either declined in number. closer to the equator, or they completely disappeared.

However, the most accurate evidence comes from isotopes. Differences in isotope ratios between fossils, sedimentary rocks and ocean sediments can reveal a lot about the environment in which they formed. Speaking of the current ice age, we also have access to ice cores obtained from Antarctica and Greenland, which are the most reliable form of evidence to date. When formulating their theories and predictions, scientists rely on a combination of these whenever possible.

Great Ice Ages
Scientists are now confident that there have been five major ice ages over the course of Earth's long history. The first of these, known as the Huronian glaciation, occurred approximately 2.4 billion years ago and lasted about 300 million years, considered the longest. The Cryogenic Ice Age occurred about 720 million years ago and lasted until 630 million years ago. This period is considered the most severe. The third massive glaciation occurred about 450 million years ago and lasted about 30 million years. It is known as the Ando-Saharan Ice Age and caused the second largest mass extinction in Earth's history, after the so-called Great Dying. Lasting for 100 million years, the Karoo Ice Age occurred between 360 and 260 million years ago and was caused by the emergence of land plants, the remains of which we now use as fossil fuels.

Finally, we have the Pleistocene Ice Age, also known as the Pliocene-Quaternary Glaciation. It began approximately 2.58 million years ago, and since then there have been several periods of glaciations and interglacial periods ranging from approximately 40,000 to 100,000 years apart. However, over the past 250,000 years, the climate has changed more frequently and dramatically, with the previous interglacial period interrupted by numerous cold periods that lasted several centuries. The current interglacial period, which began approximately 11,000 years ago, is atypical due to the relatively stable climate that has existed up to that point. It is safe to say that humans would not have been able to engage in agriculture and reach our present level of civilization if it were not for this unusual period of temperature stability.

Witchcraft
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For several centuries, beginning around 1300 and ending around 1850, the world experienced a period known as the Little Ice Age. Several factors were required for global temperatures to drop, especially in the Northern Hemisphere, causing mountain glaciers to grow, rivers to freeze, and crops to fail. In the mid-17th century in Switzerland, several villages were completely destroyed due to encroaching glaciers, and in 1622 even the southern part of the Bosphorus Strait around Istanbul completely froze. In 1645 the situation worsened and continued for the next 75 years, during the period known to scientists today as the Maunder Minimum.

There were few sunspots during this time. These spots are areas on the surface of the Sun where the temperature is significantly lower. They are caused by the concentration of magnetic fluxes in our star. On their own, these spots are likely to help cool Earth's temperature, but they are surrounded by very bright regions known as faculae. Faculae have a significantly higher emission power, which far exceeds the weak glow caused by sunspots. Thus, a sun without sunspots actually has lower levels of radiation than normal. It is estimated that during the 17th century, the Sun dimmed by 0.2 percent, which partially explains this Little Ice Age. During this time, more than 17 volcanic eruptions occurred around the world, further weakening the sun's rays.

The economic hardships caused by this centuries-long cold spell have had an incredible psychological impact on people. Frequent crop losses and firewood shortages caused serious cases of mass hysteria to break out in Salem, Massachusetts. In the winter of 1692, twenty people, fourteen of whom were women, were hanged on charges of being witches and responsible for all the misfortunes of the others. Five others, two of whom were children, later died in prison on the same charges. Due to unfavorable weather in places like Africa, even today people sometimes accuse each other of being witches.

Earth is a snow globe
The first ice age on Earth was also the longest. As we mentioned earlier, it lasted as long as 300 million years. Known as the Huronian Glaciation, this incredibly long and cold period began about 2.4 billion years ago, at a time when only single-celled organisms existed on Earth. The landscape looked very different than it does today, even before the ice covered everything. However, a series of events occurred that ultimately led to an apocalyptic event of global proportions, which left most of the planet covered in thick ice. Before the Huronian glaciation, the Earth was dominated by anaerobic organisms that did not require oxygen. Oxygen was essentially poisonous to them and an extremely rare element in the air, making up only 0.02% of the atmosphere. But at some point another form of life arose - cyanobacteria.

This tiny bacterium was the first to ever use photosynthesis as a form of nutrition. A byproduct of this process is oxygen. As these tiny creatures flourished in the world's oceans, they released millions upon millions of tons of oxygen, increasing its concentration in the atmosphere to 21% and triggering the extinction of all anaerobic life. This event is called the Great Oxygen Event. The air was also filled with methane, and in contact with oxygen it turned into CO2 and water. However, methane is 25 times more potent as a greenhouse gas than CO2, meaning that this conversion led to lower global temperatures, which in turn triggered the Huronian Glaciation and the first mass extinction on Earth. Sometimes volcanoes added extra CO2 to the air, causing interglacial periods.

Baked Alaska
If its name isn't clear enough, the Cryogenic Ice Age was the coldest period in Earth's long history. Today it is also the subject of much scientific controversy. One topic of discussion is whether the Earth was completely covered in ice, or whether there was a line of open water along the equator—the Snow Globe or Snowball Earth theory, as some call the two scenarios. The Cryogenic Period lasted from approximately 720 to 635 million years ago and can be divided into two major glaciation events known as the Startan (720 to 680 million years) and the Marinoan (approximately 650 to 635 million years). It is important to note that multicellular life did not exist at this point, and some believe that the snowball Earth scenario catalyzed its evolution during the so-called Cambrian Explosion.

A particularly interesting study was published back in 2009, focusing in particular on the Marinoan glaciation. According to the analysis, the Earth's atmosphere was relatively warm and its surface was covered with a thick layer of ice. This is only possible if the planet is completely or almost completely covered in ice. This phenomenon has been compared to the Baked Alaska dessert, where the ice cream does not melt immediately after it is placed in the oven. It turns out that there were a lot of greenhouse gases in the atmosphere, but contrary to expectations, this did not prevent and was in no way associated with the Ice Age. These gases were present in such large quantities due to increased volcanic activity following the breakup of the supercontinent Rodinia. It is believed that this prolonged volcanic activity helped kickstart the Ice Age.

However, the scientific community warns that something similar could happen again if the atmosphere begins to reflect too much sunlight into space. One such period could be triggered by a massive volcanic eruption, nuclear war, or our future attempts to mitigate global warming by spraying too much sulfate aerosols into the atmosphere.

Myths about flooding
When glacial ice began to melt about 14,500 years ago, water did not flow into the ocean equally across the Earth. In some places, such as North America, huge glacial lakes have begun to form. These lakes appear when the water's path is blocked by an ice wall or glacial deposits. Over 1600 years, Lake Agassiz covered an area of ​​440,000 square meters. km - more than any lake existing today. It was formed in North Dakota, Minnesota, Manitoba, Saskatchewan and Ontario. When the dam finally broke, fresh water rushed into the Arctic Ocean through the Mackenzie River valley.

This large influx of fresh water weakened ocean currents by 30%, plunging the planet into a 1,200-year period of glaciation known as the Younger Dryas. It is speculated that this unfortunate turn of events led to the destruction of the Clovis culture and North American megafauna. Records also show that this cold period ended suddenly around 11,500 years ago, with temperatures in Greenland rising to -7 degrees Celsius in just ten years.

During the Younger Dryas, glaciers replenished their ice, and as the planet began to warm again, Lake Agassiz appeared. However, this time it connected with an equally large lake known as Ojibway. Soon after their merger, another breakthrough occurred, but this time into Hudson Bay. Another cold period that occurred 8,200 years ago is known as the 8.2 kiloyear event.

Although the low temperatures lasted only 150 years, this event allowed sea levels to rise by 4 meters. Interestingly, historians have been able to link the origins of many flood myths from around the world to this time period. This sudden rise in sea level also caused the Mediterranean Sea to force its way through the Bosphorus Strait and flood the Black Sea, which was only a freshwater lake at the time.

Martian Ice Age
Ice ages beyond our control are natural phenomena that occur not only on Earth. Like our planet, Mars also experiences periodic changes in its orbit and axis tilt. But unlike Earth, where an ice age involves the growth of polar ice caps, different processes occur on Mars. Because its axis is tilted more than Earth's and the poles receive more sunlight, the Martian ice age means the polar ice caps are actually retreating and mid-latitude glaciers are expanding. This process stops during interglacial periods.

Over the past 370,000 years, Mars has slowly emerged from its ice age and entered an interglacial period. Scientists estimate that approximately 87,115 cubic kilometers of ice accumulate at the poles, with most accumulating in the Northern Hemisphere. Computer models have also shown that Mars could become completely covered in ice during glaciation. However, these studies are in the early stages, and given the fact that we are still far from fully understanding Earth's own ice ages, we cannot expect to know everything that happens on Mars. However, this research may prove useful given our future plans for the Red Planet. This also helps us a lot on Earth. "Mars serves as a simplified laboratory for testing climate models and scenarios, without oceans or biology, that we can then use to better understand Earth systems," said planetary scientist Isaac Smith.

Scientists have concluded that a new ice age could begin on Earth within 15 years.

This statement was made by scientists from a British university. In their opinion, recently there has been a significant decrease in solar activity. According to researchers, by 2020 the 24th cycle of the star’s activity will end, after which a long period of calm will begin.

Accordingly, a new ice age may begin on our planet, which has already been called the Maunder Minimum, reports Planet Today. A similar process already occurred on Earth in 1645-1715. Then the average air temperature dropped by 1.3 degrees, which led to the destruction of crops and mass starvation.

Pravda.ru previously wrote that scientists were recently surprised to discover that glaciers in the Central Asian Karakoram Mountains are growing rapidly. Moreover, the issue is not at all about the “spreading” of the ice cover. And in full growth, the thickness of the glacier also increases. And this despite the fact that nearby, in the Himalayas, the ice continues to melt. What is the cause of the Karakoram ice anomaly?

It should be noted that against the backdrop of the global trend towards a reduction in the area of ​​glaciers, the situation looks very paradoxical. Mountain glaciers from Central Asia have turned out to be "black sheep" (in both senses of the phrase), since their area is growing at the same rate as it is shrinking elsewhere. Data obtained from the Karakoram mountain system between 2005 and 2010 completely baffled glaciologists.

Let us recall that the Karakoram mountain system, located at the junction of Mongolia, China, India and Pakistan (between the Pamirs and Kunlun in the north, the Himalayas and Gandhishan in the south), is one of the highest in the world. The average height of the rocky ridges of these mountains is about six thousand meters (which is higher than, for example, in neighboring Tibet - there the average height is approximately 4880 meters). There are also several “eight-thousanders” - mountains whose height from the foot to the top exceeds eight kilometers.

So, in Karakorum, according to meteorologists, since the end of the twentieth century, snowfalls have become very heavy. Now about 1200-2000 millimeters of it fall there per year, almost exclusively in solid form. And the average annual temperature remained the same - ranging from five to four degrees below zero. It is not surprising that the glacier began to grow very quickly.

At the same time, in the neighboring Himalayas, according to forecasters, significantly less snow began to fall over the same years. The glacier of these mountains was deprived of its main source of nutrition and, accordingly, “shrank”. It is possible that the matter here is a change in the routes of snow air masses - they used to go to the Himalayas, but now they turn to the Karakoram. But in order to confirm this assumption, it is necessary to check the situation with the glaciers of other “neighbors” - the Pamirs, Tibet, Kunlun and Gandhisishan.