Peering down through the layers that make up Earth – the crust, the upper mantle, the lower mantle, and the core – is no easy task. There isn’t a cross-section on the planet that can be studied.
Scientists believe they have found a new mineral in Earth’s lower mantle. This section accounts for 55 percent of Earth’s total volume.
We already know about the layer’s three main minerals – bridgmanite, ferropericlase and davemaoite – but there could well be another. Researchers have been puzzled for some time by the idea that bridgmanite, davemaoite, and ferropericlase could theoretically combine at high temperatures due to their similar crystal arrangements (technically called a a Structure made of perovskite).
However, this has not been proven by previous experiments.
“Why don’t davemaoite & bridgmanite merge despite having very similar atomic-scale structures?” Over the past two decades, researchers have been fascinated by this question.” Dan (Sang-Heon Shim) is a geoscientistArizona State University
“While many attempts have been made at finding conditions in which these two minerals can merge, experiments consistently show that they are two distinct minerals. This is why we felt the experiments needed fresh ideas.
Researchers attempted to recreate the conditions found in the lower mantle through a series high-pressure heating experiments. Importantly, they were able quickly to raise temperatures, reaching temperatures of 1,650 to 1,925 degrees Celsius (3,000-3,000,500 degrees Fahrenheit), in less than a second. After that, temperatures reached temperatures of approximately 2,800 degrees Celsius.
The small, heated samples – now at temperatures representative of the topmost layer of the lower mantle down to the deep lower mantle – were then observed through X-ray imaging to map the structure of its minerals. Unexpectedly, at temperatures of around 2,000 degrees Celsius, one perovskite minerals formed, a combination from bridgmanite & davemaoite.
This suggests that the deeper mantle has a different mineralogy than the higher-pressure section. It is due to greater pressure and temperature. Researchers believe that iron plays an important role in the fusion of davemaoite and bridgmanite lower down.
“It was believed that there is a large difference in the size of calcium and magnesium, both major cations of davemaoite or bridgmanite. This would hinder the two minerals from merging.” Byeongkwan, a mineralogistMichigan State University
“But our study has shown that they can overcome this difference in hot environments,”
Earth’s mantle was previously much hotter than it is today, which suggests that perovskite mineral merging would have been more prevalent – and therefore that the geological composition has been altered significantly over time.
These results are in line with previous researchThis suggests that the properties of lower mantles change as it gets deeper. This is something that future studies will be able to analyze further – both in terms of its current state and its state in the past.
The researchers write in their report that “Our discovery requires revision of deep-mantle mining models and will have an effect on our understanding the composition, structure dynamics and evolution of this region.” Published paper.
The research has been published in Nature.
