<P> Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms . Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago . Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive . In the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events . Over 99% of all species that ever lived on Earth are extinct . Estimates of the number of species on Earth today vary widely; most species have not been described . Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival . Humans have developed diverse societies and cultures; politically, the world has about 200 sovereign states . </P> <P> The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe . It has cognates in every Germanic language, and their proto - Germanic root has been reconstructed as * erþō . In its earliest appearances, eorðe was already being used to translate the many senses of Latin terra and Greek γῆ (gē): the ground, its soil, dry land, the human world, the surface of the world (including the sea), and the globe itself . As with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, and later Norse mythology included Jörð, a giantess often given as the mother of Thor . </P> <P> Originally, earth was written in lowercase, and from early Middle English, its definite sense as "the globe" was expressed as the earth . By Early Modern English, many nouns were capitalized, and the earth became (and often remained) the Earth, particularly when referenced along with other heavenly bodies . More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets . House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant . Another convention capitalizes "Earth" when appearing as a name (e.g. "Earth's atmosphere") but writes it in lowercase when preceded by the (e.g. "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?" </P> <P> The oldest material found in the Solar System is dated to 7000456720000000000 ♠ 4.5672 ± 0.0006 billion years ago (Bya). By 7000454000000000000 ♠ 4.54 ± 0.04 Bya the primordial Earth had formed . The bodies in the Solar System formed and evolved with the Sun . In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun . A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10--7001200000000000000 ♠ 20 million years (Mys) to form . </P>

What is the real name of the earth