Chihuahua Dog Breed. First discovered in Mexico, the Chihuahua is best known for being the smallest dog breed in the world. Extremely loyal to its owner, the breed has recently become a popular culture icon in the United States, most notably Paris Hilton's Chihuahua, Tinkerbell. Physical Characteristics.
Earth formed around 4.54 billion years ago by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean; but the atmosphere contained almost no oxygen and so would have been toxic to most modern life including humans.
Earth began to cool, and solid rock formed on the surface and volcanic activity took place. 1. Earth was struck by a large body that caused the planet to melt. 2. Earth began to cool, and solid rock formed on the surface and volcanic activity took place. 3. Earth's surface was cool enough for water to remain liquid.