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.
Most of the Earth's early atmosphere was created in the first one million years after solidification (4.4 billion years ago). Carbon dioxide, nitrogen, and water vapor dominated this early atmosphere. Table 5b-1 below describes the three major stages of development of the atmosphere.