This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Why is there life on Earth? It's one of the oldest questions humans have asked, and as far as we know, our planet is the only one that holds the answer.
Earth is also the only planet we know of with plate tectonics, the slow-motion churn of its outer shell that recycles rock, reshapes continents and cycles the nutrients that could feed life. A new international study, published in Nature Geoscience and led by Dr. Hugo Moreira, a Royal Society university research fellow at the University of Portsmouth, is helping us better understand the origins of life by tracing the deep history of Earth's oxygen back billions of years, to a time when the planet and its atmosphere looked nothing like they do today.
To look that far back, Moreira's team turned to one of the toughest minerals on Earth, known as zircon. These tiny crystals can survive largely unchanged for billions of years, and using lasers at the university's Mass Spectrometry and Laser Ablation Lab, scientists can date them with remarkable precision—in this study, pinpointing some samples to exactly 3.4 billion years old. Some of these zircons contain a second, smaller mineral called apatite, trapped inside like a fly in amber.
Because it's sealed inside the tougher zircon, this apatite is protected from change, meaning it's exactly the same age as its host. "These minerals are really exciting to scientists, as they are essentially time capsules," said Moreira from the university's Institute of the Earth and Environment. "Because they're so well protected, we can analyze their chemical fingerprints to get an untouched snapshot of a moment billions of years in the past.
We're looking into the early Earth, when it was a very different planet, and figuring out what we can still see of it today." The team collaborated with an international network of researchers and investigated ancient rock samples from around the world—including Australia, Finland, South Africa, Brazil and Scotland—which were sent to Portsmouth for initial analysis. The samples were then taken to the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, one of the most powerful X-ray facilities in the world, where researchers used a specialized technique to measure the chemical state of sulfur trapped inside each tiny apatite crystal. The form that sulfur takes acts as a highly sensitive chemical fingerprint.
It reveals how much oxygen was present when the crystal formed, at the point where the planet's outer shell is dragged down and recycled into its interior—a process called subduction. "These crystals are tiny, often narrower than a human hair, and they contain only small amounts of sulfur," explained co-author Marine Cotte, the scientist in charge of ID21, the ESRF beamline where the measurements were carried out. "So, we needed an X-ray beam that was very fine, very sensitive and fast enough to measure lots of crystals.
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