Reference Terms
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Ice age
An ice age is a period of long-term reduction in the temperature of Earth's climate, resulting in an expansion of the continental ice sheets, polar ice sheets and mountain glaciers. Glaciologically, ice age is often used to mean a period of ice sheets in the northern and southern hemispheres; by this definition we are still in an ice age (because the Greenland and Antarctic ice sheets still exist). More colloquially, when speaking of the last few million years, ice age is used to refer to colder periods with extensive ice sheets over the North American and Eurasian continents: in this sense, the most recent ice age ended about 10,000 years ago.
There are three main types of evidence for ice ages: geological, chemical, and paleontological. Geological evidence for ice ages comes in various forms, including rock scouring and scratching, glacial moraines, drumlins, valley cutting, and the deposition of till or tillites and glacial erratics. Successive glaciations tend to distort and erase the geological evidence, making it difficult to interpret. It took some time for the current theory to be worked out.
There have been at least four major ice ages in the Earth's past. Outside these periods, the Earth seems to have been ice-free even in high latitudes.
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Earth & Climate News
October 26, 2025
Oct. 26, 2025 — New research shows that hippos lived in central Europe tens of thousands of years longer than previously thought. Ancient DNA and radiocarbon dating confirm they survived in Germany’s Upper Rhine Graben during a milder Ice Age phase. Closely ...
Oct. 26, 2025 — Scientists have uncovered that glaciers can temporarily cool the air around them, delaying some effects of global warming. This self-cooling, driven by katabatic winds, is nearing its peak and will likely reverse in the next two decades. Once ...
Oct. 25, 2025 — For the first time, scientists have seen a subduction zone actively breaking apart beneath the Pacific Northwest. Seismic data show the oceanic plate tearing into fragments, forming microplates in a slow, step-by-step collapse. This process, once ...
Oct. 24, 2025 — Scientists have discovered that El Niño and La Niña could become far more powerful and predictable as the planet warms. By 2050, the tropical Pacific may hit a tipping point, locking ENSO into strong, rhythmic oscillations that synchronize with ...
Oct. 23, 2025 — In the mist-shrouded mountains of New Guinea, a Czech researcher has achieved a world-first — capturing photos, video, and data of the elusive Subalpine Woolly Rat, Mallomys istapantap. Once known only from museum specimens, this giant, shaggy ...
Oct. 23, 2025 — Sea levels are rising faster than at any time in 4,000 years, scientists report, with China’s major coastal cities at particular risk. The rapid increase is driven by warming oceans and melting ice, while human activities like groundwater pumping ...
Oct. 23, 2025 — Scientists have uncovered evidence that megaquakes in the Pacific Northwest might trigger California’s San Andreas Fault. A research ship’s navigational error revealed paired sediment layers ...
Oct. 22, 2025 — Common dolphins in the North Atlantic are living significantly shorter lives, with female longevity dropping seven years since the 1990s. Researchers found this decline by analyzing stranded dolphins, revealing a 2.4% drop in population growth ...
Oct. 21, 2025 — Scientists are taking the once-radical concept of dimming the sun through stratospheric aerosol injection (SAI) seriously, but a Columbia University team warns that reality is far messier than models suggest. Their study reveals how physical, ...
Oct. 21, 2025 — Melting Arctic ice is revealing a hidden world of nitrogen-fixing bacteria beneath the surface. These microbes, not the usual cyanobacteria, enrich the ocean with nitrogen, fueling algae growth that supports the entire marine food chain. As ice ...
Oct. 19, 2025 — Researchers have developed a light-emitting sugar probe that exposes how marine microbes break down complex carbohydrates. The innovative fluorescent tool allows scientists to visualize when and where sugars are degraded in the ocean. This ...
Oct. 13, 2025 — Humanity has reached the first Earth system tipping point, the widespread death of warm-water coral reefs, marking the beginning of irreversible planetary shifts. As global temperatures move beyond 1.5°C, the world risks cascading crises such as ...
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Oct. 19, 2025 — Mars’ north polar vortex locks its atmosphere in extreme cold and darkness, freezing out water vapor and triggering a dramatic rise in ozone. Scientists found that the lack of sunlight and moisture ...
Oct. 17, 2025 — Researchers have discovered chemical fingerprints of Earth's earliest incarnation, preserved in ancient mantle rocks. A unique imbalance in potassium isotopes points to remnants of “proto Earth” ...
Oct. 16, 2025 — Ryugu’s samples reveal that water activity on asteroids lasted far longer than scientists thought, possibly reshaping theories of how Earth gained its oceans. A billion-year-old impact may have ...
Oct. 16, 2025 — Researchers discovered a new field of ancient tektites in South Australia, revealing a long-forgotten asteroid impact. These 11-million-year-old glass fragments differ chemically and geographically ...
Oct. 16, 2025 — New research reveals that Earth’s continents owe their stability to searing heat deep in the planet’s crust. At more than 900°C, radioactive elements shifted upward, cooling and strengthening ...
Oct. 12, 2025 — Supershear earthquakes, moving faster than seismic waves, could cause catastrophic shaking across California. USC researchers warn that many faults capable of magnitude 7 quakes might produce these ...
Oct. 12, 2025 — Researchers are finding extraordinary new uses for what we throw away. Beet pulp may help crops resist disease, while composted coconut fibers could replace peat moss. Discarded radish and beet ...
Oct. 12, 2025 — Geophysicists have modeled how Earth’s magnetic field could form even when its core was fully liquid. By removing the effects of viscosity in their simulation, they revealed a self-sustaining ...
Oct. 10, 2025 — Coccolithophores, tiny planktonic architects of Earth’s climate, capture carbon, produce oxygen, and leave behind geological records that chronicle our planet’s history. European scientists are ...
Oct. 10, 2025 — China’s Guangdong Province is battling its worst-ever chikungunya outbreak, with thousands of infections spreading across major cities and nearby regions. Transmitted by Aedes mosquitoes, the ...