When was the last Ice Age?

An ice age is a period of long-term global cooling when large parts of the Earth’s surface is covered by ice. 

Such times saw the growth of ice sheets and glaciers that dominated the mountains at high latitudes and began spreading into lower areas as well. 

Glaciations are the particular colder phases within an ice age when these ice masses tend to expand. 

In contrast, interglacial phases are the warmer periods when the ice retreats.

During glaciations, wide areas of land become covered by thick ice. It becomes so thick that its immense weight presses down on the ground beneath it.

As it slowly moves due to gravity, the heavy ice carves valleys in the ground and created coastal features such as moraines and fjords. 

When interglacial periods take place, ecosystems begin to recover as ice sheets melted and sea levels rose, which would flood coastal areas that were exposed before.

During the Last Glacial Maximum, about 26,500 to 19,000 years ago, the Earth saw its most extreme cold phase of the last ice age. 

Huge ice sheets, which included the Laurentide Ice Sheet in North America and the Fennoscandian Ice Sheet in Europe, covered large parts of the northern hemisphere. 

Sea levels were about 120 metres (394 feet) lower than today. This exposed some iimportant land bridges such as Beringia that connected Siberia to Alaska. 

As a result, these bridges allowed humans and animals to move into new regions.

Even so, the climate was still very cold and dry, which caused some deserts to grow and vegetation zones to shift significantly.

Natural factors drove the last ice age over thousands of years through complex interactions in Earth’s climate system. 

One main cause was the Milankovitch cycles, which describe the regular changes in the Earth’s orbit, including any tilt and wobble that affect how much sunlight reaches the planet. 

When northern hemispheric sunlight was reduced, snow and ice built up and created reflective surfaces that made cooling stronger. 

A process of increased reflectivity known as the 'albedo effect' helped glaciers and ice sheets grow as well. 

Also, changes in greenhouse gas levels helped keep ice age conditions going. 

Carbon dioxide and methane levels, measured in ice core samples, stayed much lower during glacial periods. 

Gases like these trap heat in the atmosphere. However, the rates of these gases fell because cold oceans absorbed more carbon dioxide.

This led to less plant growth in colder climates, which cut natural emissions. 

That weaker greenhouse effect made the cooling trend stronger and kept the icy environment.

However, tectonic shifts could also change ocean currents and moved heat around the globe. 

The rise of the Isthmus of Panama, which linked North and South America, blocked warm water flowing between the Atlantic and Pacific Oceans. 

This rerouting of warm-water flows redirected currents and cooled the northern hemisphere. 

Finally, volcanic eruptions added to cooling by releasing ash and sulfur dioxide into the atmosphere, which sent incoming sunlight back into space and caused short-term drops in temperature. 

As glaciers advanced, large areas of land became too harsh and many species, who had to move to milder regions. 

For example, mammoths and woolly rhinoceroses suited to cold conditions moved south during glacial expansions. 

Species that needed warmer climates retreated to isolated refuges: small areas of suitable habitat that offered shelter. 

Such migrations caused 'genetic bottlenecks' that affected evolution and reduced genetic diversity.

As habitats changed, some species developed traits that let them survive extreme conditions. 

Large mammals like saber-toothed cats and dire wolves grew strong bodies to conserve heat and hunt in snowy environments. 

Plants also adjusted to the colder climate. Tundra vegetation, including hardy shrubs and grasses, spread across formerly forested areas. 

Plants like these adapted with shorter growing seasons and a resistance to frost. 

However, many species could not adapt fast enough and went extinct, especially large megafauna at the end of the Ice Age.

During the Ice Age, early humans adapted to harsh and changing climates through new survival methods and great resourcefulness. 

Because they depended on their environment for survival, they developed tools and methods to maximise the use of the limited resources they found. 

Stone tools such as flint blades and scrapers were crafted to process animal hides because they were essential for creating strong clothing and shelter. 

Fire also became a key part of daily life because it provided warmth and protection. 

As glacial advances transformed the terrain, early humans migrated in search of better conditions and new resources. 

An exposed land bridge between Siberia and Alaska due to lower sea levels called Beringia became an important migration route. 

It enabled groups to move into uninhabited areas of the Americas and adapt to a range of environments, ranging from tundra to temperate forests. 

Such migrations must have required careful planning because they included the need to store and transport food.

Humans also learned to hunt large Ice Age megafauna, including mammoths and mastodons. 

These animals provided meat, fur, and bone. To do this, weapons such as spears and atlatls were developed, along with teamwork strategies that were required to make hunting more effective. 

Also, humans gathered edible plants, roots, and berries in addition to hunting to add variety to their diets. 

Seasonal migration patterns of the game animals they were hunting meant early humans had to remain highly mobile and aware of environmental changes.

Around the end of the Ice Age, orbital changes that were part of the Milankovitch cycles increased solar radiation in the Northern Hemisphere. 

It began a gradual warming starting around 19,000 years ago. It began melting the vast ice sheets that had dominated the planet during the Last Glacial Maximum. 

As temperatures rose, melting ice sheets in North America, Europe, and Asia released huge amounts of freshwater into the oceans.

Over the next several millennia, sea levels to rose and started to flood previously exposed coastal areas. 

The sudden warming event known as the Bølling-Allerød interstadial around 14,000 years ago brought milder conditions to many regions around the world. 

However, the change was not steady because a short return to cooler conditions occurred during the Younger Dryas period approximately 12,900 years ago and was likely triggered by disruptions in ocean currents. 

When warming resumed shortly after, the melting of glaciers changed the Earth’s climate system and led to further ice loss and rising sea levels.

Massive ice dams such as the one that held Glacial Lake Missoula also broke apart, releasing massive floods that carved out new terrain features. 

Floods like these were sudden and huge, and carried sediment and water over great distances. 

The influx of freshwater into the oceans disrupted thermohaline circulation and further influenced global weather patterns.

As the ice sheets diminished, previously glaciated regions experienced major ecological and geological changes. 

The release of pressure from the melting ice, a process called isostatic adjustment, let the Earth's crust rise, raise land levels, and change river systems. 

The growth of temperate ecosystems replaced tundra in many areas, which created further new habitats for flora and fauna. 

Rising sea levels flooded low-lying regions and covered land bridges such as Beringia.

This had the effect of isolating populations and changing migration routes for both humans and animals.

Finally, the Holocene epoch began the current interglacial period by ending the ice age approximately 11,700 years ago. 

Onset of the Holocene triggered rapid deep environmental changes vital for the development of human societies. 

Glaciers moved back to polar regions, and the warming climate supported the growth of forests and grasslands, allowing humans to establish permanent settlements and cultivate crops.