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 object known 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