Why do scientist say a thousand million instead of one billion in terms of years
Carl Sagan speaks a great deal about the age of the universe. Often you will notice he references time in terms of thousands of millions. People commonly are stumped about this reference. "instead of saying a thousand million why doesn't he just say a billion," you ask? The reason for this conundrum is because in other places such as Latin America and parts of Europe the term Billion doesn't have the same value as it does here in America. A thousand million to America is the number that is represented as a one followed by 9 zeros, and that would be the short value which is 1,000,000,000. In Britain, however a Billion is a Million Millions also known in America as 1 trillion. The numeric value of a Million is universal across the globe while Billion is not always the same. So that is why Scientist such as Carl Sagan state thousands of millions instead of just stating the short answer of a billion.
Additional notes of understanding are that a Billion in Europe is often referred to as a Millard.
And lastly to answer your question the earths age is four-thousand five hundred forty million years old. Give or take 45.4 million years.