An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Cores are drilled with hand augers (for shallow holes) or powered drills; they can reach depths of over two miles, and contain ice up to 800,000 years old. The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core. The ratio of oxygen and hydrogen isotopes provides information about ancient temperatures, and the air trapped in tiny bubbles can indicate the level of atmospheric gases such as carbon dioxide. Greenland ice cores contain layers of wind-blown dust that correlate with cold, dry periods in the past. Radioactive elements, either of natural origin or created by nuclear testing, can be used to date the layers of ice. Some volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different cores that can be used to synchronize their time scales. Climate models can be constructed by piecing together all the available data.

Read more: https://en.wikipedia.org/wiki/Ice_core

_______________________________ Today's selected anniversaries:

1081:

Byzantine–Norman wars: Robert Guiscard led an invasion of the Byzantine Empire, capturing Dyrrhachium in present-day Albania. https://en.wikipedia.org/wiki/Battle_of_Dyrrhachium_(1081)

1561:

Sengoku period: The fourth battle of Kawanakajima, one of the most famous in Japanese history, was fought in present-day Nagano Prefecture. https://en.wikipedia.org/wiki/Battles_of_Kawanakajima

1851:

Moby-Dick, a novel by American writer Herman Melville, was first published as The Whale in London. https://en.wikipedia.org/wiki/Moby-Dick

1929:

In the Persons Case, the Judicial Committee of the Privy Council decided that women were eligible to sit in the Canadian Senate. https://en.wikipedia.org/wiki/Edwards_v_Canada_(AG)

1967:

The Soviet space probe Venera 4 (replica pictured) became the first spacecraft to perform direct in situ analysis of the environment of another planet (Venus). https://en.wikipedia.org/wiki/Venera_4

_____________________________ Wiktionary's word of the day:

henotheism: Belief in or worship of one deity without denying the existence of other deities. https://en.wiktionary.org/wiki/henotheism

___________________________ Wikiquote quote of the day:

A country, after all, is not something you build as the pharaohs built the pyramids, and then leave standing there to defy eternity. A country is something that is built every day out of certain basic shared values.   --Pierre Trudeau https://en.wikiquote.org/wiki/Pierre_Trudeau