Earth©

Based on the available evidence, scientists have been able to reconstruct detailed information about my past. I am believed to have formed around 4.55109 years ago out of the solar nebula, along with the Sun and other planets. The moon formed soon afterwards. Initially molten, the outer layer of the planet cooled, resulting in the solid crust. Outgassing and volcanic activity produced the primordial atmosphere; condensing water vapor, augmented by ice delivered by comets, produced the oceans. The highly energetic chemistry is believed to have produced a self-replicating molecule around 4109 years ago, and half a billion years later, the last common ancestor of all life lived.

The development of photosynthesis allowed the sun's energy to be harvested directly; the resultant oxygen accumulated in the atmosphere and gave rise to the ozone layer. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. Cells within colonies became increasingly specialized, resulting in true multicellular organisms. With the ozone layer absorbing harmful ultraviolet radiation, life colonized my surface. Over hundreds of millions of years, continents formed and broke up as my surface continually reshaped itself. Since the Cambrian explosion, about 535 million years ago, there were 5 distinct mass extinctions.

The last one occurred 65 million years ago, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, which then resembled shrews. Over the last 65 million years, mammalian life diversified, and several million years ago, a small African ape gained the ability to stand upright. As brain size increased, these hominids developed the use of tools and language. The development of agriculture, and then civilization allowed humans to affect me in a short timespan like no other life form had before, affecting both the nature and quantity of other life forms as well as global climate.

It takes the Me, on average, 23 hours, 56 minutes and 4.091 seconds (1 sidereal day) to rotate around the axis connecting the north pole and the south pole. From Me the main apparent motion of celestial bodies in the sky (except meteors which are within the atmosphere and low-orbiting satellites) is the movement to the west at a rate of 15 °/h = 15'/min, i.e., a Sun or Moon diameter every two minutes.

I orbit the Sun every 365.2564 mean solar days (1 sidereal year). From this, i give an apparent movement to the Sun with respect to the stars at a rate of about 1 °/day, i.e., a Sun or Moon diameter every 12 hours, eastward. The orbital speed is an averages of about 30 km/s (108,000 km/h), which is enough to cover one Earth diameter (~12,600 km) in 7 minutes, and one distance to the Moon (384,000 km) in 4 hours.

I have one natural satellite, the Moon, which revolves with Me around a common barycenter, from fixed star to fixed star, every 27.32 days. When combined with the Earth-Moon system's common revolution around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. The Hill sphere (sphere of influence)I create is about 1.5 Gm (930,000 miles) in radius.

Viewed from my north pole, the motion of me, my moon and our axial rotations are all counterclockwise. The orbital and axial planes are not precisely aligned: My axis is tilted some 23.5 degrees against the Earth-Sun plane (which causes the seasons); and the Earth-Moon plane is tilted about 5 degrees against the Earth-Sun plane (otherwise there would be an eclipse every month).

In an inertial reference frame, my axis undergoes a slow precessional motion with a period of some 25,800 years, as well as a nutation with a main period of 18.6 years. These motions are caused by the differential attraction of Sun and Moon on my equatorial bulge, due to its oblateness. In a reference frame attached to me, its rotation is also slightly irregular due to polar motion. The polar motion is quasi-periodic, containing an annual component and a component with a 14-month period called the Chandler wobble. Also, the rotational velocity varies, a phenomenon known as length of day variation.

In modern times, Earth's perihelion is always about January 3, and aphelion is about July 4 (near the solstices, which are on about December 21 and June 21). For other eras, see precession and Milankovitch cycles. The Earth is sometimes referred to as the Third Planet from the Sun because, of the nine planets of our solar system, Earth is the third closest planet to the sun.