Experts on Earth

Earth (also the world^{[n 5]}, in Greek: Γαῖα Gaia,^{[n 6]} or in Latin: Terra^[26]) is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical objectknown to harbor life. The earliest life on Earth arose at least 3.5 billion years ago.^[27][28][29] Earlier physical evidences of life include graphite, a biogenic substance, in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland,^[30] as well as, "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.^[31][32] Earth's biodiversity has expanded continually except when interrupted by mass extinctions.^[33] Although scholars estimate that over 99 percent of all species of life (over five billion)^[34]that ever lived on Earth are extinct,^[35][36] there are still an estimated 10–14 million extant species,^[37][38] of which about 1.2 million have been documented and over 86 percent have not yet been described.^[39] Over 7.3 billion humans^[40]live on Earth and depend on its biosphere and minerals for their survival. Earth's human population is divided among about two hundred sovereign states which interact through diplomacy, conflict, travel, trade and communication media.

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