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.
For the next 1.3 billion years (3.8 to 2.5 billion years ago), the Archean Period, first life began to appear and the worldâs landmasses began to form. Earthâs initial life forms were bacteria, which could survive in the highly toxic atmosphere that existed during this time.