So how old is the earth? Some people think the Bible says it was created about 6,000 years ago. While the Bible does include a number of genealogies, many conservative Bible scholars believe that these lists are not intended to be a complete method of dating the age of the earth. Instead God gave us another means to discover this kind of information: he created the natural world through faithful, consistent processes. And as we observe these processes and their effects today, we can develop reliable conclusions about the past.
Most people know that tree rings are a record of growth from year to year. If we look at the cross section of a tree today and find 75 rings, this is a window into the past 75 years, including the atmospheric conditions of each year. And rings from the same years can be correlated among the petrified remains of trees of different ages, providing an unbroken record from the present back to more than 13,000 years ago.
There are other dating methods that use layers too, like the annual ice layers at the poles of the earth, which have been measured to over 100,000 years in Greenland, and over 700,000 years in Antarctica! These methods allow us to determine information about the past from data that is available today.
Another method counts “varves” which are found at the bottom of many lakes. During the summer months the lakes are fed by streams that carry a lot of sediment. The heavier particles settle on the bottom, but many of the finer particles stay in circulation around the lake. In the winter when the water freezes, the circulation of the lake slows down and allows the finer particles to settle on the bottom too. This process creates distinctive layers that can be counted just like tree rings, some going back more than 50,000 years. When these layers harden into sedimentary rock, millions of years of deposits can be preserved.
Another important way of determining the age of the earth is called radiometric dating. Some elements have radioactive versions which decay over time. This time period is called the “half-life”, which is the amount of time it takes for half of the original substance to decay. For example, the Carbon-14 half-life is about 5,730 years. Plants continuously absorb Carbon-14 while living, but the amount goes down at a constant rate when they die. The remains of plants (or animals that have eaten them) can be dated by measuring how much is left. If you find that half of the original amount of C14 is left, then the living thing died 5,730 years ago. Original amounts can be calibrated with tree ring and varve dating, and this provides a reliable measure of time for living things back to about 50,000 years ago.
Other forms of radiometric dating work on non-living objects and provide much longer timescales. Potassium 40 has a half-life of 1.3 billion years. Using this method, rocks in Greenland have been dated to over 3.6 billion years ago.
There are many other independent means of determining the age of the natural world. These are incredibly consistent with each other and point to the earth being created four and a half billion years ago. Such an immense span of time is also consistent with what we learn about God from Scripture. He doesn’t seem to be in a hurry, but works patiently through the ages to bring about his intentions—think of 40 years wandering in the desert, centuries waiting for the Messiah, or millennia for the return of Christ. The God we encounter in the Bible is the same God who created this vast and ancient universe. In the next video we’ll start looking at the process he used to bring about the diversity of life on earth.