What is the estimated age of the Earth?

It is believed that the Earth is 4-5 billion years old. Almost nothing is known of the Earth’s conditions during the first billion years before the consolidation of its crust. Through some methods like tidal force, sedimentation, rate of erosion, salinity of the ocean and radioactivity, the Earth’s age has been estimated but still debatable. The Big Bang theory, which explains the formation of the universe, was postulated in the 1950s and 1960s and its validity in 1972, proved by evidence received from the Cosmic Background Explorer is now accepted.