The Earth

Earth, also called the world and, less frequently, Gaia and Terra in some works of science fiction, 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 accommodate life.

The earliest life on Earth arose at least 3,5 billion years ago. Earth's biodiversity has expanded continually except when interrupted by mass extinctions. Although scholars estimate that over 99% of all species of life that ever lived on Earth are extinct, there are still an estimated 10-14 million extant species, of which about 1,2 million have been documented and over 86% have not yet been described. 

Over 7,3 billion humans 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.

According to evidence from radiometric dating and other sources, Earth was formed about 4, 54 billion years ago. Within its first billion years, life appeared in its oceans and began to affect its atmophere and surface, promoting the proliferation of aerobic as well as anaerobic organisms and causin the formation of the atmophere's ozone layer.

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 Jöro, a giantess often given as the mother of Thor.

Venus

Venus is the second planet from the Sun, orbiting it every 224,7 Earth days. It has no natural satellite. It is named after the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of -4.6, bright enough to cast shadows. Because Venus is an inferior planet from Earth, it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8º.

Venus is a terrestrial planet and is sometimes called Earth's "sister planet" because of their similar size, mass, proximity to the Sun and bulk composition. It is radically different from Earth in other respects. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide.

The atmospheric pressure at the planet's surface is 92 times that of Earth's. With a mean surface temperature of 735K (462 ºC; 863 ºF), Venus is by far the hottest planet in the Solar System, even though Mercury is closer to the Sun. Venus has no carbon cycle that puts carbon into rock, nor does it seem to have any organic life to absorb carbon in biomass.

Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid, preventing its surface from being seen from space in visible light. It may have had oceans in the past, but these would have vaporized as the temperature rose due to a runaway greenhouse effect. The water has most probably photodissociated, and, because of the lack of a planetary magnetic field, the free hydrogen has been swept into interplanetary space by the solar wind.

Venus's surface is a dry desertscape interspersed with slab-like rocks and periodically refreshed by volcanism. 

Mercury

Mercury is the smallest and closest to the Sun of the eight planets in the Solar System, with an orbital period of about 88 Earth days. Seen from Earth, it appears to move around its orbit in about 116 days, which is much fster than any other planet in the Solar System. It has no known natural satellites. The planet is named after the Roman deity Mercury, the messenger to the gods.

Because it has almost no atmosphere to retain heat, Mercury's surface experiences the greatest temperature variation of the planets in the Solar System, ranging from 100 K(-173 ºC and -280 ºC) at night to 700 K  (427 ºC; 800 ºF) during the day at some equatorial regions. The poles are constantly below 180 K (-93 ºC; -136 ºF).

Mercury's axis has the smallest tilt of any of the Solar System's planets (about 1/30 of a degree), but ithas the largest orbital eccentricity. At aphelion, Mercury is about 1,5 times as far from the Sun as it is at perihelion. Mercury's surface is heavily cratered and similar in appearance to the Moon, indicating that it has been geologically inactive for billions of years.

Eagle

Eagle is a common name for many large birds of prey of the family Accipitridae; it belongs to several groups of genera that are not necessarily closely related to each other. Most of the sixty species of eagles are from Eurasia and Africa. Outside this area, just fourteen species can be found - two in North America, nine in Central and South America, and three in Australia.

Eagles are large, powerfully built birds of prey, with a heavy head and beak. Even the smallest eagles, like the booted eagle (Aquila pennata) (which is comparable in size to a common buzzard (Buteo buteo) or re-tailed hawk (B. jamaicensis)), have relatively longer and more evenly broad wings, and more direct, faster flight - despite the reduced size of aerodynamic feathers. Most eagles are larger than any other raptors apart from some vultures.

The smallest species of eagle is the South Nicobar serpent eagle (Spilornis klossi), at 450 g (1 lb) and 40 cm (16 in). The largest species are discussed below. Like all birds of prey, eagles have very large hooked beaks for tearing flesh from their prey, strong muscular legs, and powerful talons. The beak is typically heavier than that of most other birds of prey. Eagles' eyes are extremely powerful, having up to 3,6 times human acuity for the martial eagle, which eanbles them to spot potential prey from a very long distance.

This keen eyesight is primarily attributed to their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light. The female of all known species of eagle is larger than the male. Eagles normally build their nests, called eyries, in tall trees or on high cliffs. Many species lay two eggs, but the older, larger chick frequently kils its younger sibling once it has hatched. 

The dominant chick tends to be the female, as they are bigger than the male. The parentes take no action to stop the killing.

Sharks

Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date back to more than 420 million years ago.

Since then, sharks have diversified into over 505 species. They range in size from the small dwarf lanternshark, a deep sea species of only 17 centimetres 6,7 inch) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 foot) in length. 

Until the 16th century, sharks were known to mariners as "sea dogs". The etymology of the word "shark" is uncertain. One theory is that it derives from the Yucatec Maya word "xok", pronounced "shok". Evidence for this etymology comes from the Oxford English Dictionary, which notes shark first came into use after Sir John Hawkins' sailors exhibited one in London in 1569 and posted "sharke" to refer to the large sharks of the Caribbean Sea. 

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Balaenidae

Balaenidae is a family of whales of the suborder mysticete that contains two living genera. Historically, it is known as the right whale family, as it was thought to contain only species of right whales.

Through most of the 20th Century, however, that became a much-debated (and unresolved) topic amongst the scientific community. Finally, in the early 2000s, science reached a definitive conclusion: the bowhead whale, once commonly known as the Greenland right whale, was not in fact a right whale.

The family of Balaenids, therefore, comprises the right whales (genus Eubalaena), and in a genus all to its own, the very closely related bowhead whale (genus Balaena). Their principle distinguishing feature is their narrow, arched, upper jaw, which gives the animals a deeply curved jawline. This shape allows for especially long baleen plates.

Snakes

Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with their highly mobile jaws.

To accommodate their narrow bodies, snakes´paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one fuctional lung. Some species retain a pelvic girdle with a pair of estigial claws on either side of the cloaca.

Living snakes are found on every continent except Antarctica, and on most smaller land masses - exceptions include some large islands, such as Ireland and New Zealand, and many small islands of the Atlantic and central Pacific. Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans.