How Reliably Determined Is Earth’s Age?

Question of the Week: Young-earth creationists believe all the ways scientists date the earth at 4.5 billion years are inaccurate. They believe it is only about 6,000–10,000 years old. What do you tell people about how reliable the old-earth data is?

My Answer: Young-earth creationist scientists acknowledge that if the radiometric decay rates are constant or even approximately constant, then both the universe and Earth must be billions of years old (see the Radioisotopes and the Age of the Earth or RATE books published by the Institute of Creation Research and the Creation Research Society). However, their hypothesis that the radiometric decay rates were accelerated by a factor of a million to a billion times at the fall of Adam and/or the flood of Noah is both biblically and scientifically untenable.

The Bible repeatedly declares or implies that the laws of physics are constant. For example, in Jeremiah 33 God accuses the people of Judah of being fickle, always changing their minds. God replies by saying that he never changes. Then he offers an analogy. He states that as the laws that govern the heavens and the earth never change, likewise he does not change. Some other passages declaring the constancy of physics are Genesis 3, Ecclesiastes, and Romans 8.

Astronomical observations also prove that the laws of physics are constant. In observing the distant light of stars and galaxies, astronomers can measure the values of the constants of physics, including rates of radiometric decay and the velocity of light, when the light left those stars and galaxies. Their measurements establish that physics has been constant throughout the past 12 billion years of light travel time.     

The date for Earth’s age is very reliable. It has been measured to 4.5662±0.0001 billion years based on the measured decays in primitive meteorites (the building blocks of Earth) of uranium-238, uranium-235, and thorium-232 into lead-206, lead-207, and lead-208, respectively. (There is no natural source of lead other than the radiometric decay of heavier-than-lead radioisotopes.) In my book A Matter of Days, 2nd edition, I give multiple independent evidences for an accurate, assumption-free date for Earth’s age as well as for the universe’s age.