<s>[INST] How old are the earth? [/INST] The age of the Earth is, according to current knowledge, 4.54 billion years.</s>\ <s>[INST] For this result, what is considered to be "the start" of the "existence of earth"? that is, what event or condition is used to mark the beginning of this period? [/INST] Condensation or aggregation of dust, interstellar material with the help of gravity to concentrate and form a celestial (planetary) body.</s>