Final answer:
James Ussher used Biblical chronology as a source to calculate the age of the Earth, but his method is not scientifically accurate. Radiometric dating is the primary method used by scientists today.
Step-by-step explanation:
James Ussher used Biblical chronology as one of the sources to calculate the age of the Earth. He relied on the genealogies and events described in the Bible to estimate the time since creation.
It is important to note that Ussher's calculation of the age of the Earth based on Biblical chronology is not considered scientifically accurate by modern standards. Today, scientists primarily use radiometric dating to determine the age of the Earth by measuring the decay of radioactive elements in rocks and minerals.