John Creech
Apil 2012
John is into his 2nd year of a PhD where he is using platinum isotopes in meteorites to answer questions about how the Earth formed.
"My PhD is looking at the relative abundance of different isotopes of platinum to answer these big questions. It's funded by a Marsden grant and a Victoria PhD scholarship, he said.
A discrepancy exists between the amount of platinum we would expect in the crust and mantle, and what we actually find. One idea is that after Earth had largely formed, it was bombarded by meteorites which brought extra platinum and other metals from space. By comparing the platinum isotope ratios in samples of Earth’s crust and mantle, 'primitive' meteorites (the same rocks that were raining down during the bombardment) and iron meteorites (that are similar to Earth's core material), we hope to be able to tell whether the metals came from the bombarding material or not.
"What makes it tricky is that there is not much platinum in most rocks. In the ones we are looking at, platinum is typically present in the part per billion (ppb) range. One part per billion is the equivalent of three seconds in a hundred years of time, so it’s very, very little. We have to chemically extract the platinum from the samples and then use our extremely sensitive instruments to measure the levels of the different isotopes.
"Meteorites are quite hard to get. People prospect for them in deserts and on the ice – places you wouldn't usually find rocks. You can request samples from NASA or buy them online, but some rare types cost thousands of dollars per gram. Fortunately, we only need small amounts and have already built up a modest collection in the School.
A. Typical iron meteorite, made of iron-nickel metal. These meteorites represent the cores of 'planetesimals' that existed in the early Solar System.
B. Carbonaceous chondrite. Chondrites were forming in space at the same time as the Solar System. This specimen contains small white inclusions of refractory material which are the oldest solids in the Solar System.
C. Slice of iron meteorite etched to reveal the octahedral crystalline structure of the different iron-nickel alloys it is composed of.
John's journey to this point has been unconventional but prepared him well for his PhD. He began studying astronomy, then moved to Victoria to study physics, but it was a geology course he took at the same time that really sparked his interest. “I knew immediately that I wanted to stay on and do postgraduate research in geology – I just fed on the lecturers’ enthusiasm.
Geology led to geochemistry and now includes cosmochemistry – using the chemistry of rocks from space to solve big questions in the Solar System.
"During the course of my study I've been able to use all of the leading edge instruments in the geochemistry lab, which is great experience to have.
"I’ve really enjoyed being at Victoria, especially the field trips that are a big part of a geology degree. I still take every opportunity I get to go along as a tutor or helper. I think it’s a unique opportunity for students to interact with academic staff and learn about their research. Our staff are a very inspiring bunch and are top notch internationally. That has definitely been a factor in me staying on at Victoria for my PhD."