What we take for the history of nature is only the very incomplete history of an instant" - Denis Diderot

In a moment of weakness I turned the TV on (the only screen I usually watch is one with a computer attached to it) a couple of nights ago and watched a religious program on the age of the Earth. The "scientist" was explaining how all of our current methods of dating elements, estimating the rate of erosion, and the rate of sedimentary build up were completely wrong in determining the age of the Earth. The age of the Earth, he concluded, can be no more than 6,000 years old, with dinosaurs roaming the Earth as little as 4,000 years ago.

I was intrigued. How do we know with certainty how old the Earth really is? We do know that the Earth is at least 5,000 years old as we have written records dating back to 3,000 BC, or BCE if you prefer.

I decided to look back into the records to see how our present day notion that the Earth is 4.6 billion years old was arrived at.

Our western civilization held that the Earth was 6,000 years old right up to the 1800's. They held this belief based on faith in the teachings of the Bible, but science is not based on faith, but rather on observations and evidence.

A French scholar, Bernard Palissy who lived from 1510-1589 believed the Earth was much older based on his observations that rain, wind, and tides were the cause for much of the present-day appearance of the Earth. He wrote that, these forces could not work over such a short period of time to produce the changes. He was burned at the stake in 1589. A bad time for scientific inquiry.

Another was Thomas Burnet, a member of the English clergy, who lived from 1635-1715. He had written a book around 1681 supporting the idea of a worldwide flood, but in 1692, he wrote another book in which he questioned the existence of Adam and Eve, and that ended his career.

The notion that the Earth is much older than 6,000 years comes from a book written in 1795 by James Hutton, called "The Theory of the Earth" Hutton presented evidence that slow, gradual changes acting over a long period of time were responsible for shaping much of the Earth's landmasses. It took almost 50 years for science to begin to accept Hutton's ideas. Hutton's ideas became known as uniformitarianism.

Science began to study the changes taking place at the present time and worked out how rapidly those changes were happening. The assumption is that if the rate of change remains more or less constant, then the time it takes to create the change could be estimated mathematically.

Edmund Halley was the first person to attempt to calculate the rate of change. His idea was to determine the rate at which the oceans became salty. He observed that the fresh water rivers carried salt, dissolved from the land during the process of erosion, to the oceans. Halley thought that at one time the oceans must have been free of salt, and the salt contained in them must have been carried there by the rivers. So he set out to find out how much salt the rivers carried into the oceans each year. He arrived at an age of 1 billion years for the oceans to reach their present levels of salinity.

In 1896, only one hundred years ago, French physicist, Antoine Henri Becquerel discovered by accident that atoms of uranium gave off radiation. Marie Currie studied the phenomenon further and concluded that the radiation was the result of radioactivity. In 1915, Frederick Soddy discovered that over time the radioactive atoms of uranium and thorium broke down into simpler elements. This decay continued until lead was produced, which is not radioactive, and the decay stopped.

Ernest Rutherford, working with Soddy, showed that every radioactive element had a half-life. This being the amount of time it takes for half of the radioactive atoms to be lost. The half life of uranium turns out to be around 4.5 billion years, thorium has a half life of 14 billion years. This set an upper limit for the age of the Earth. If the Earth was a trillion years old, no radioactive uranium could exist.

Bertram Boltwood an American physicist worked out how to calculate the age of rocks containing uranium and lead. Boltwoods method took into account that the rock might contain some naturally occurring lead. He was able to isolate an isotope which was not present in lead formed through radioactive decay, but was only present in lead formed naturally. Using this method some rocks were dated at more than 1 billion years old. In 1931, rocks were found that were 3.8 billion years old in Greenland.

The point: There is some evidence today that scientific inquiry is on the wane, that people seem to accept the mystical more readily than the empirical.   Our view of the universe is based on what we see and what we reason the cause can be to explain what we see. This is the difference between humans and animals.