1. Ice sheets and glaciers are key components of ice ages.
The Utah Geological Survey defines an ice age as “a long interval of time … when global temperatures are relatively cold and large areas of the Earth are covered by continental ice sheets and alpine glaciers.” Basically, a weirdly cold winter or five wouldn’t be an ice age, but millions of years of chilly temperatures with ice sheets and glaciers would.
2. Glaciers once wiped out worms across much of North America.
For thousands of years, there were barely any earthworms across a large swath of North America. The animals all but vanished from the northern part of the continent around 10,000 years ago, and it wasn’t because they were gobbled up by some sort of prehistoric early bird: Glaciers caused their demise.
During Earth’s most recent glaciation period, which peaked around 20,000 years ago, glaciers crept across the northern latitudes, grinding and scouring everything in their path. Soft, squishy earthworms were no match for the heavy ice. For thousands of years, much of the continent’s soil was without earthworms—that is, until European colonists inadvertently introduced hordes of the creepy crawlies to the landscape.
3. Earth has had periods of extreme heat and cold.
Over its 4.5-billion year history, Earth has swung between periods of extreme heat and extreme cold. Crocodile-like reptiles once lurked within the lakes of the North Pole and palm trees swayed in Antarctic breezes.
4. Acid rain may indirectly lead to planetary cooling.
There are a number of factors that might help plunge the planet into an ice age, and some explanations aren’t particularly intuitive. You probably know that increased carbon dioxide levels in the atmosphere can warm the planet, but they might also have the opposite effect, given the right set of conditions.
460 million years ago, the volcanic eruptions that helped create parts of the northern Appalachian Mountains dumped record-breaking amounts of CO2 into the atmosphere. It’s believed that all that carbon created acid rain. As geochemist Lee Kump explained to the Earth science publication EOS, when acid rain “‘attacks silicate rocks like granites and basalts,’ a chemical reaction incorporates the CO2 into limestone, which removes the molecule from the atmosphere.” More carbon in rocks and ocean floor sediment and less in the atmosphere might have contributed to the Earth’s cooling.
That volcano example is a somewhat speedier version of what’s sometimes called the slow carbon cycle, in which carbon moves between rocks, soil, the ocean, and the atmosphere over hundreds of millions of years.
Because rocks can sequester carbon—remove it from the atmosphere and store it in a form that doesn’t contribute to the greenhouse effect—scientists are interested in what factors might slow down or accelerate the weathering processes that break down rocks and lead to this sequestration. The formation of large mountain ranges, like the Himalayas, is often at the center of these investigations. Some believe that the formation of these mountains causes increased weathering, which could then allow more carbon from the air to get stored in rocks
5. Changes in the planet’s orbit and tilt can contribute to ice ages.
The planet’s orbit and the tilt of its axis aren’t as constant as you might think, and variations in them can contribute to ice ages. These changes happen regularly over the course of hundreds of thousands of years, affecting the amount of sunlight that different latitudes on Earth receive, and by extension, the planet’s temperature. When the angle of Earth’s tilt decreases, summers cool down, allowing snow to accumulate. As layers of snow condense into glaciers and ice sheets, they reflect more sunlight—and therefore heat—causing global temperatures to drop.
6. Ice ages go through periods of freezing and thawing.
Each of the major ice ages themselves went through cycles of freezing and thawing, called glacial and interglacial periods. During an interglacial period, glaciers recede toward the poles but don’t completely disappear. This ebb and flow of ice and heat is a long process that plays out over a span of tens of thousands of years, so you can probably cross off an instant planetary freeze, à la 2004’s The Day After Tomorrow, from your list of climate concerns.
7. The first of Earth’s five major ice ages was the Huronian glaciation.
The first of Earth’s five major ice ages was the Huronian glaciation, which kicked off about 2 billion years ago, possibly helped by a 250-million year pause in volcanic activity. That ice age was so intense that the entire planet froze over to form the first of a few “snowball Earths.” (Though many geologists think “slushball earth” would be a more accurate label, as the planet may not have been entirely frozen.)
8. Land plants may have caused the Karoo ice age.
It’s believed land plants caused the Karoo, or Late Paleozoic, ice age, which started around 360 million years ago. As plants covered the planet, they sucked carbon dioxide from the atmosphere and released oxygen into the air, which caused temperatures to once again plummet.
9. “The ice age” often refers to the Quaternary glaciation.
When people talk about the ice age, they aren’t talking about any random glaciation period. They’re referring to the most recent glaciation during the Pleistocene epoch of the Quaternary period. (An epoch is a timeframe within a period; a period is a longer timeframe within an era.) So when we refer to the ice age, going forward, we’re talking about a specific timeframe that lasted from about 120,000 to 11,500 years ago.
10. The formation of the Isthmus of Panama may have contributed to the ice age.
It’s believed tectonics played a big role in triggering the Quaternary Glaciation—more specifically, the formation of the Isthmus of Panama, the strip of land that links North and South America. The land bridge divides the Atlantic and Pacific Oceans. When it formed, it drastically changed both oceans’ currents, as the warm, tropical water could no longer flow between them. The warmer water went north, causing more precipitation in the Northern Hemisphere’s high latitudes. This precipitation—which, at high latitudes, fell as snow—kept piling up and freezing to form glaciers and ice sheets. All that ice reflected more light and absorbed less heat than the darker oceans it now covered, creating a positive feedback cycle that further decreased the planet’s temperature.
11. The ice age reached its peak around 20,000 years ago.
The ice age reached its height, a period called the Last Glacial Maximum, around 20,000 years ago. Back then, 8 percent of the Earth’s surface, and a quarter of the planet’s total land area, was buried beneath ice. Ice sheets up to a mile thick covered North America—including a whopping 97 percent of Canada—as well as large parts of Northern Europe, Asia, and Patagonia.
Other parts of Northern Europe were basically transformed into a tundra, wiping out the warm-weather plants that had previously thrived there. Steppes, which are flat, unforested grasslands, expanded across the planet and sub-Saharan Africa became more arid. Because of all the water locked in frozen ice sheets at the time, the sea level was 400 feet lower than it currently is.
12. During the Last Glacial Maximum, the planet’s average temperature was around 46°F.
During the Last Glacial Maximum, on average, the planet’s temperature hovered around 46°F. That’s 11 degrees colder than the 20th century’s average global temperature. And average Arctic temperatures back then were 25 degrees cooler than today’s.
