2.1.1: Birth of the Solar System
Earth is the third planet from the Sun, one of eight "classical" planets recognized by the International Astronomical Union in our solar system . A planet must orbit the Sun, be big enough that gravity pulls it into a round ball, and must have other things out of its orbital path. Pluto, defined as a planet until 2006 but was declassified as it orbits among the icy bits of the asteroid belt. In 2008 it was classified as a "plutoid", a kind of dwarf planet .
It is thought that the planet like Earth originated from the accretion of bits of solid matter left from the massive explosion of a star or supernova. Bits of material were scattered into space forming a slowly rotating cosmic gas cloud. Gravity slowly gathered the thinly spread atoms of the cosmic cloud. As the atoms moved closer together the gas became hotter and more dense. A new sun was born as hydrogen eventually became so tightly compressed and temperatures so high that nuclear burning began. A flattened rotating disc of gas and dust surrounded the young sun. Outer cooler parts of the disc or star nebulae began to condense to form the building blocks of future planets.
Video : "Birth of the Solar System" Courtesy National Geographic