You may have been aware that our Earth is as old as 4.5 billion years. But do you know who found out this fantastic figure first? The destiny rests on shoulders on a young man, Clair Patterson, who was a PhD student at the University of Chicago in the 1940s. I’d like to share his story with you!
The first task for Patterson was to measure the concentration and isotope composition of lead inside the zircon, which is extremely useful for geological dating. The lead present in zircon indicates the decay from uranium, appearing to serve as an accurate clock (details see: https://en.wikipedia.org/wiki/Uranium-lead_dating). Moreover, if the composition of the world’s primordial lead (e.g. from iron meteorites, as origins of the Earth and meteorites should be related) can be figured out, scientists are supposed to tell the Earth’s age!
Iron meteorite found in Canyon Diablo (figure credit: Geoffrey Notkin)
This was a brilliant idea however followed by tough laboratory work. It was found that no matter how crazy Patterson measured the concentration and isotope composition of lead in the zircon sample, disappointing results always showed up – exceeding values with poor reproducibility. Then, it was realized that there must be some lead coming from outside the lab or even the atmosphere that contaminated the samples and ruined nearly all the experiments!
To this end, Patterson began to clean his laboratory by hand, trying to wipe all the lead away from the working area. It wasn’t in vain, but still not much improved…… Things turned out to be better until Patterson and his supervisor, Harrison Brown, moved to Caltech where the world’s first ultra-clean room was built up. The hope just came along.
Clair Patterson working at Caltech (Photo credit: Caltech E&S Magazine)
Here by saying ‘ultra-clean’ I mean the air coming to the room is filtered and the dust is excluded – you know dust is dusty. The cleanroom then became a necessary for the metal isotope research across the world’s laboratories (see: https://en.wikipedia.org/wiki/Cleanroom) and to my knowledge it marks the cornerstone of ‘trace-level’ exploration.
It had been 7 years since the young man began to study the lead, and finally he made it! These were Patterson’s whispers: Thank you Charles Lyell (the author of Principles of Geology)… Thank you Ernest Rutherford (the father of nuclear physics)… Thank you Harrison Brown (dear supervisor)…Thanks to all the scientists who had contributed to field… Thanks to the state-of-the-art analytical technique (multiple collector inductively coupled plasma mass spectrometry, https://en.wikipedia.org/wiki/Isotope-ratio_mass_spectrometry)… Here we go: it is 4.5 billion years – the Earth’s age!!!
The lead-lead isochron for meteorites (Patterson, 1956)
It appears to be a happy ending, however I would say, this is just the beginning. At the time of wiping down the interferences of lead from the laboratory, Patterson began to think about the sources of lead. Afterwards Patterson got the chance to further investigate the vertical distribution of lead in the oceans, and what surprised him was that the concentration of lead in shallow water was hundreds of times greater than in deep ocean… The most contaminated areas were close to the east and west coasts of the United States where the vehicle industry was highly developed… Based on investigations from the polar ice core, the lead level was even hundreds of times greater than the geological past…
All these facts points a mass ‘poisoning’ on an unprecedented scale, as for many years lead has been known to cause brain damage, development impairment, violent behaviour, and even death. Nonetheless, the addition of tetraethyl lead (https://en.wikipedia.org/wiki/Tetraethyllead) to gasoline as an antiknock agent has become a practice since 1921. Patterson went public with his discoveries about lead, publishing the findings and sending copies to government leaders. He fought against the industry for another 20 years and his efforts accelerated the phaseout of lead from all standard, consumer, automotive gasoline in the US in the 1980s.
Clair Patterson’s story inspired me a lot: the man who figured out the Earth’s age was also responsible for one of the greatest public health victories of the 20th century!
Patterson, C. C. (1956). Age of meteorites and the Earth. Geochim. Cosmochim. Acta 10, 230-237.
deGrasse Tyson, N., Druyan, A., Braga, B., & Pope, B. (2014). Cosmos: A spacetime odyssey. National Geographic Series. Available at: http://channel.nationalgeographic.com/cosmos-a-spacetime-odyssey.