However, when did the continents emerge out of the ancient ocean? That is still not clear today. “People would probably agree it was around 2.7 to 2.5 billion years ago when the continents emerged,” Alex says. “But some papers published in the last few years say that happened perhaps as late as 700,000 years ago. Alternatively, some people even say it was right at the start of Earth's history.”
Aside from the timing there is one other question that still does not have a definitive answer. “We don't know how this process occurred. Was it super rapid, was it gradual, or did it happen in stages?”
This is why Alex is using his expertise in geochemistry as well as the latest technology to analyse rock samples that are billions of years old and gain a deeper understanding of what exactly happened and when.
Studying changes over time in rocks from Western Australia
As a geochemist, Alex says his work is essentially applying chemistry to understand rocks. “Geochemistry is when you look at the different compositions of rocks to understand their formation. It's all based on elements and isotopes, which are also atoms, but with different numbers of neutrons,” Alex says and adds that neutrons are sub-atomic particles with a ‘neutral’ charge.
In this respect, Alex is especially interested in looking at changes over time in rock samples from Western Australia. These samples are drill cores that used to be the ocean floor billions of years ago. “I am looking for the primary ocean signature,” Alex says. “But it's not the ocean water, it's the ocean floor sediments that have turned into rock, that I am interested in. This is what is telling us about the oceans two or three billion years ago.”
Researching banded iron formations
In his current Discovery Early Career Researcher Award (DECRA) research project, Alex is focusing on banded iron formations, which are called such because the rock samples show ‘bands’ of iron in between other sediments.
“I have lots of samples from the Hamersley Basin, which is just south of the Pilbara region in Western Australia. That's where we find these massive iron deposits that are about 2.6 to 2.4 billion years old,” Alex says. “I also have samples from the Yilgarn, which lies east of Perth, that are 2.7, and some from the Pilbara that are over three billion years old.”