Fred Jourdan

Dating Rocks with Fred Jourdan

A Table and a Desk

Building 312 is another one of Curtin University’s original buildings. Its brick is old and the carpet is ancient. Gleaming elevators, a modern amenity, transport me to the third floor where I follow the trajectory of room numbers to land at 313. The Professor ushers me into his large den with a table taking up half the room, a desk taking up a quarter and the rest is filled with chairs. I see little sign of geology here. That is because he has his own lab as part of the John de Laeter Centre two floors below. Much like the volcanoes that drew him into the study of rocks, he erupts into conversation.

Itokawa

In 2005, 25143 Itokawa was the first sample return mission. The samples were returned, by Hayabusa, to Earth on 13 June 2010. ‘The Japanese, they brought back sample from Itokawa.’ The sample return mission was a partial failure in that it only brought back a few, miniscule grains. ‘They studied it for a year. Then they opened it to the experts around the world. I told them with my technique; I use a laser that vaporises the grain. You will never see them again. At first, they sent me two grains. I destroyed them. They saw the results. I asked for more grain, they sent. That opened my taste for planetary science.’

Scientists Are Gone Dating Rocks

39Ar/40Ar are radioactive isotopes the Professor uses to woo rocks, revealing their ages. ‘Inside banana, there’s potassium. Inside you, there’s potassium. There’s a tiny bit of this potassium which is radioactive. So, you are radioactive, I’m radioactive and your banana is even more radioactive because there’s a lot of potassium. There’s also potassium in all the rocks. Pretty much every crystal. Sometimes it’s atoms that make the crystal itself. There’s going to be potassium. Potassium decays in Argon. Half of it will decay in 1.2 billion years.’ Using argon-argon dating, scientists can date volcanic rocks and minerals as old as four billion years. This form of dating rocks is one of the most accurate methods for studying Earth’s history and asteroids and meteorites. Argon-39 (^39Ar) is a radioactive isotope with a half-life of about 269 years. Argon-40 (^40Ar) is a stable isotope that is the product of the radioactive decay of potassium-40 (^40K). The Professor continued his explanation of how he dates rocks. ‘If you have a bathtub, and you know that you’re putting one liter per minute in the bathtub, then you go away and come back. You stop the time. There’s 10 liters of water in the bathtub meaning you’ve been away for 10 minutes. Potassium is the tap, and Argon is the water. By measuring the ratios, you calculate the age of the rock.’

Necessary Transformation

Potassium-40 is like a ticking atomic clock. Over time, ^40K naturally breaks down and transforms into Argon-40, which gets trapped in rocks. Scientists measure how much ^40Ar has built up to figure out how long that clock has been ticking. In Argon-Argon dating, they convert Potassium-39 into Argon-39 using a nuclear reactor. Then they measure the ratio of Argon-40 to Argon-39 to calculate the age more precisely. ‘We send our sample into a low-power nuclear research reactor in Oregon, USA, to change this potassium into another type of Argon. Argon-39 is a gas. We can use a single instrument to measure gas and a gas, which is much easier than a solid on one instrument and a gas on another instrument.’

Precision

Dating rocks is vital because it helps scientists build a reliable timeline of Earth’s history from the formation of continents to the evolution of life. Without precise dates, we’d just be guessing when major events like volcanic eruptions, mass extinctions or climate shifts happened. Carbon dating is not accurate enough for geologists. ‘With Carbon dating, you can date stuff up to 40,000, 50,000. Which, for a geologist, is yesterday.’ 39Ar/40Ar and Uranium/Lead dating are important game changers for unraveling the mysteries of both Earth and our Solar System. Many asteroids and meteoroids hurtling around our stellar neighbourhood have been around since the formation of our Solar System. With the Professor’s method, researchers discover how old these rocks are, proving the true age of the solar system.

Contaminants

‘You can have easy contamination.’ Contamination means that unwanted materials or substances have mixed in with the sample you’re trying to study, messing up results. In rock dating, for example, if newer Argon gas sneaks into an old rock, it can make the rock seem younger or older than it really is. ‘You know if your age or your number you get is accurate or not. You know if it has been contaminated and you can correct it. If you can’t, then you know your analysis failed. With some techniques, such as Carbon dating, you put your sample in the machine, it gives you some data and you calculate the number. You don’t know if this number is correct or not. But we know with 39Ar/40Ar or Uranium/Lead technique if it’s correct or not. We use statistics and we compare if the system has been perturbed, contaminated or opened. We can see this right away.’ Even a small amount of contamination can throw off the age calculation, making it crucial to detect and correct.

To the Lab and Beyond

After diving deep into the science of dating rocks and contamination, the Professor was eager to show me where the magic happens. It must be a dream to be the Head of the Geology discipline at Curtin University with your very own lab for those casual moments where you have the urge to stare through a tube at a grain of space rock a mere few billion years old. My eyes popped when I saw a room full of equipment. I felt like an intruder and did not want to breathe on anything.

The Professor handed me a tiny fragment of outer space informing me that it had been floating around our Solar System since the very beginning. Holding a fragment of space rock older than Earth itself was humbling. It was a reminder of how far science can reach. I also had the unique opportunity to gaze down some microscope tubes at space grains. In that moment, surrounded by billion-year-old grains and cutting-edge instruments, I understood why dating rocks isn’t just about numbers, it’s about unlocking the story of our planet and the universe beyond.

Written by Louise Kaestner, 2025. For more, visit LinkedIn or head to her website: https://www.louisekaestnerwriter.com/