Age of the "Earth."

Article Here

I have seen this number in another source.

"Considering that Doctrine and Covenants 77:6 refers to “…this earth during the seven thousand years of its continuance, or its temporal existence,” what led Phelps to speak of Earth as 2,555 million years old? The answer appears to be straightforward. Though 7000 Earth years is in conflict with all physical, chemical, genetic, archaeological, and linguistic evidence, 7000 years of God is not ruled out. The arithmetic is easy. One day of God is 1000 years of man, and therefore in Joseph Smith’s reckoning, a day of God is 365 × 1000 days of man. The 2.555 billion years in question therefore corresponds to 2,555,000,000/365,000 years of God, which is 7000 years of God for each day of Earth’s existence. A more careful calculation, using the true average length of the year including leap years (365.257 days) gives 2,556,799,000 Earth years. Clearly Joseph Smith did not intend the “7000 years” of Earth’s age to refer to Earth years.

The same number surfaces again in Elder McConkie’s address, “The Seven Deadly Heresies,” delivered at BYU in 1980. He refers to God as “an infinite and eternal being who has presided in our universe for almost 2,555,000,000 years,”6 but without any indication of the source or significance of that number."