Our planet did not come with a guidebook. It has taken generations of scientists building upon one another’s ideas and research to compile our current understanding of the earth’s systems and history. However, our planet did come with clues to its long history, and it is the work of geologists, archaeologists, and others to sleuth through these clues and put the pieces together. Methods for accurately dating historical events, situating moments of Earth’s history in place and time are an essential part of earth science. In this paper, I will discuss one clue that scientists have leveraged to solve the mysteries of Earth’s past. This is the isotope carbon 14, which can be used to date objects and artifacts up to 50, 000 years old (MacDougall, 2008:190).

I will first give some essential background on the methods that scientists use to date organic and inorganic materials, and discuss geochronology as a discipline. I will recount the story of the discovery of carbon 14’s usefulness for dating, and how our knowledge regarding the uses of this isotope has changed over time. I will explain how and why carbon 14 works as a recorder of time, and describe some notable cases when it has proven useful for dating human artifacts and other relics. Lastly, I will review some case studies of interesting uses of radiocarbon dating in research today. The investigation of earth’s past has a fascinating social history. James Hutton, working as a geologist during the Industrial Revolution, believed that the earth worked rather like a machine. Surrounded by industry, and Darwin and science’s understanding of evolution, Hutton hypothesized that Earth history progressed in cycles, repeating the same patterns over and over again on an inconceivably long time scale (MacDougall, 2008:8-11). This concept was widely accepted until some years later, when Lord Kelvin cast doubt upon it. Based upon research in deep mines, Kelvin believed that planet earth was hot inside, and cooling over time. As a physicist, Kelvin believed that if he could estimate the earth’s original temperature, and determine the rate at which the planet was cooling, then he could mathematically determine the age of the earth (MacDougall, 2008:14).

While neither Hutton nor Kelvin was completely correct in his strategy for dating the earth, their theories were hugely impactful for science. Hutton’s theory contributed the idea that the earth goes through “cycles”, and that geologic time is extremely long (MacDougall, 2008:11). Kelvin’s research was ingenious, but incomplete. In fact, if Lord Kelvin had added just a few more figures to his equation, it would have worked perfectly to date the earth. But no one had yet discovered the convection of the mantle, or the existence of radioactive materials within it (MacDougall, 2008:16). There were many other thinkers who undertook to develop a strategy for dating the Earth around Kelvin’s time, and although these strategies and the theories behind them were creative, they did not contribute as much to science. George Darwin, for example, believed the speed of the earth’s rotation to be slowly decreasing, estimated its original speed and rate of slowing, and claimed that the earth was 50 to 60 million years old (MacDougall, 2008:15). John Joly believed that the earth’s oceans were getting saltier over time, and that he could determine its age using the amount of salt in the sea and the rate at which rivers deposited it over time (MacDougall, 2008:15). These theories may sound mad to us now, but they were mostly based on sound logic, and the knowledge that existed at the time.