How Do We Know the World Is 4.6 Billion Years Old?

Metal Accumulation in the Oceans

• One method looks at the length of time certain metals have been present in the ocean. The time spans range from 100 years (aluminum) to 260,000,000 years (sodium).

  This dating method does not account for any processes that remove metals from the ocean, however.

Radiometric Dating

• Radiometric dating refers to the dating processes used on rocks. Geologists have found many ancient rocks across the globe, but as the constant processes of plate tectonics and erosion continually break rocks down, it is difficult to derive a definitive age.

  However, "the Earth must be at least as old as any formation on it," says the Talk Origins Archive.

  Therefore, as geologists have found rocks that are at least 4.2 billion years old, it follows that the Earth will be much older, taking into account the rocks' natural erosion and destruction.

Meteorite Dating

• The idea behind dating meteorites is based on the fact that they are not as prone to destruction as rocks and are likely to have formed at the same time as the planets of our solar system, including the Earth.

  The rubidium-strontium method dated at least 15 samples of H Chrondites at an average age of 4.59 billion years and 11 samples of Eucrites at approximately 4.44 billion years old.

  This method is troublesome, as we cannot be entirely sure of the similarities between meteorite ages and the age of the earth. Put together, however, these three methods (and more besides) point to the same likely age of 4.6 billion years, with over 99 percent certainty, according to the U.S. Geological Survey.