Earth Ebook

Earth (otherwise known as 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.

According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.[27][28][29] Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 solar days or one sidereal year.[n 7] Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days).[30] The Moon is Earth's only permanent natural satellite. Its gravitational interaction with Earth causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.[31]

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. 71% of Earth's surface is covered with water,[32] with the remainder consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere. Earth's polar regions are mostly covered with ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the magnetic field, and a convecting mantle that drives plate tectonics.

Within its first billion years,[33] life appeared in Earth's oceans and began to affect its atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Since then, the combination of Earth's distance from the Sun, its physical properties and its geological history have allowed life to thrive and evolve. The earliest undisputed life on Earth arose at least 3.5 billion years ago. Earlier physical evidence of life includes biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland, as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.[34][35] Earth's biodiversity has expanded continually except when interrupted by mass extinctions.[36] Although scholars estimate that over 99% of all species of life (over five billion)[37] that ever lived on Earth are extinct,[38][39] there are still an estimated 10–14 million extant species,[40][41] of which about 1.2 million have been documented and over 86% have not yet been described.[42] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[43] Over 7.3 billion humans[44] live on Earth and depend on its biosphere and minerals for their survival. Earth's human population is divided among about 200 sovereign states that interact through diplomacy, conflict, travel, trade, and communication media.

地球（也称为世界[N 5]希腊：Γαῖα盖亚，[N 6]或拉丁文：兵马俑[26]）是从太阳，在太阳系中密度最大的行星，最大的第三颗行星太阳系的四大类地行星，和已知的存在生命的唯一天体。

根据放射性测年和证据其他来源，地球形成约4.54十亿年前。[27] ​​[28] [29]地球引力在太空中其他物体，特别是太阳和月亮交互。在绕太阳轨道，地球绕其自身轴线366.26倍，产生365.26太阳能天或恒星年。[N 7]旋转地轴倾斜23.4°远离其轨道平面的垂直，在生产季节变化地球上有一个为期回归年（365.24太阳日）。[30]表面月球是地球唯一的天然永久性卫星。其与地球引力相互作用导致海洋潮汐，稳定地球旋转轴的取向，并且逐渐减缓地球旋转速率。[31]

地球的岩石圈被划分成整个表面上的数百万年时间几迁移刚性板块。地球表面的71％被水覆盖，[32]与由大陆和一起有许多湖泊和其它水源，有助于水圈岛屿的剩余部分。地球极地地区大多覆盖着冰，包括南极冰盖和北极冰包的海冰。地球内部仍然活跃了坚实的铁内核，其产生的磁场一个液态外核和地幔对流驱动板块构造。

内的第一十亿年，[33]寿命出现在地球上的海洋和开始影响其气氛和表面，导致好氧和厌氧微生物的增殖。自那时以来，来自太阳，其物理性能和其地质历史地球距离的组合已经允许生活茁壮成长和发展。地球上最早的生命无可争议的出现至少3.5十亿年前。生命的早期实物证据包括在西南格陵兰岛发现了3.7十亿岁的沉积岩生物石墨，以及4.1十亿岁岩石在西澳大利亚发现的“遗骸生物的生命。”[34] [35]地球的生物多样性已经当大灭绝打断，除了不断扩大。[36]尽管学者估计，生活的所有物种（五年十亿）的99％以上[37]是有史以来地球上灭绝，[38] [39]有仍估计有10-14亿的现存种，其中[40] [41]约120万已被记录在案，并超过86％，尚未说明。[42]最近，2016年5月，科学家报告说，1万亿种估计是地球上当前与所描述的百分之一只有千分之一。[43]超过730十亿人[44]住在地球上和取决于它的生物圈和矿物质为他们的生存。地球上的人类人口中，通过外交，战争，旅游，贸易，通信媒体互动约200主权国家分裂。