An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and greenhouse periods during which there are no glaciers on the planet. Earth is currently in the ice age called Quaternary glaciation. Individual pulses of cold climate within an ice age are termed glacial periods, and intermittent warm periods within an ice age are called interglacials or interstadials.
An artist's impression of ice age Earth at Pleistocene glacial maximum
Haukalivatnet lake (50 meters above sea level) where Jens Esmark in 1823 discovered similarities to moraines near existing glaciers in the high mountains
Stages of proglacial lake development in the region of the current North American Great Lakes
Scandinavia exhibits some of the typical effects of ice age glaciation such as fjords and lakes.
Earth is the third planet from the Sun and the only astronomical object known to harbor life. This is enabled by Earth being a water world, the only one in the Solar System sustaining liquid surface water. Almost all of Earth's water is contained in its global ocean, covering 70.8% of Earth's crust. The remaining 29.2% of Earth's crust is land, most of which is located in the form of continental landmasses within Earth's land hemisphere. Most of Earth's land is somewhat humid and covered by vegetation, while large sheets of ice at Earth's polar deserts retain more water than Earth's groundwater, lakes, rivers and atmospheric water combined. Earth's crust consists of slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth has a liquid outer core that generates a magnetosphere capable of deflecting most of the destructive solar winds and cosmic radiation.
The Blue Marble, Apollo 17, December 1972
A 2012 artistic impression of the early Solar System's protoplanetary disk from which Earth and other Solar System bodies were formed
Pale orange dot, an artist's impression of Early Earth, featuring its tinted orange methane-rich early atmosphere
Conjectured illustration of the scorched Earth after the Sun has entered the red giant phase, about 5–7 billion years from now