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>
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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>
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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>
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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>