Earth, also known as Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. It is the largest of the solar system's terrestrial planets, and the only planetary body that modern science confirms as harboring life. Scientific evidence indicates that the planet formed around 4.57 billion (4.57×109) years ago, and shortly thereafter (4.533 billion years ago) acquired its single natural satellite, the Moon.
Its astronomical symbol consists of a circled cross, representing a meridian and the equator; a variant puts the cross atop the circle (Unicode: ? or ?). Besides words derived from Terra, such as terrestrial, terms that refer to the Earth include tellur- (telluric, tellurian, from the Roman goddess Tellus) and geo- (geocentric, geothermal; from the Greek goddess Gaia).
The word Earth has cognates in many modern as well as defunct - including ancient - languages. Examples in modern tongues include aarde in Dutch and Erde in German. The root also has cognates in extinct languages such as ertha in Old Saxon and ert (meaning 'ground') in Middle Irish. It is derived from Old English eorðe. Taking into account metathesis, we can find cognates of the word Earth in the Latin terra and in the modern Romance Languages (i.e. tierra in Spanish).
Although a link to such Indo-European languages has not been proved, several Semitic languages have similar-sounding words for Earth: aard in Arabic, irtsitu in Assyrian, araa in Aramaic, erets in Phoenician (which appears in the Mesha Stele), and ??? (arets, or erets when followed by a noun modifier) in Hebrew.
All text of this article available under the terms of the GNU Free Documentation License (see Copyrights for details).