Kyushu University Faculty of Science

Earth System Chemistry

• YAMAMOTO Junji, Professor
• ARAKAWA Masashi, Associate Professor
• FUKUYAMA Ko, Assistant Professor

Do you know that meteorites and asteroids remain in the Earth's deep interior? Our laboratory is exploring the chemical signatures of meteorites and asteroids from the Earth's mantle to clarify how the Earth came to be.

My (Junji Yamamoto's) goal is to solve one of the greatest mysteries, "how the Earth was born," using natural samples in the Earth. The reason why I am focused on the Earth's materials is that the best record of the Earth is the Earth itself. However, looking around the Earth's surface, there is no place where we can see the Earth in its original state of formation. There must be regions deep within the Earth that have been asleep since the beginning of the Earth's formation. The Earth is one of the planets. Understanding the formation of the Earth will therefore provide crucial constraints on the solar system formation model.

1. Exploration of Hadean Earth

Do you know that there are two chemical layers in mantle? Many people may think that the mantle is entirely convective (whole mantle convection). Perhaps it is wrong. The isotopic ratios of the Mid-Oceanic Ridge magma, which is derived from the shallow mantle, are quite different from those of the Oceanic Island magma, which is derived from the deep mantle. It indicates that the Earth's mantle has maintained layered mantle convection. In addition, the noble gas isotope ratios of the Oceanic Island magmas show solar wind-like properties. This fact implies that the Earth-forming components remain in the Earth's deep interior. A more chemical study of the Oceanic Island magma would provide insight into what happened on Earth in Hadean and the asteroids that built the Earth.

2. Ultra-deep borehole cores

Do you know that you can collect mantle rocks? You might say, "It is easy to collect peridotite". Because peridotites are also found in the Earth's crust, it is necessary to determine the depth from which they originated in order to say "I got it". We are developing an ultra-high-precision geo-barometer that can be applied to peridotites. We use the pressure of a small fluid contained in the peridotites as a pressure sensor. The pressure reflects the depth at which the peridotites existed in the deep Earth. If the pressure can be read, we can determine the depth provenance of the peridotites. Using this method, we can now determine the depth provenance of a peridotite with an amazing precision of about 30 ± 0.01 km. This method will draw a detailed map of the Earth's interior.

3. Global carbon cycle study

Do you know that there is 50,000 times more carbon in the Earth's interior than on the surface? The carbon on the Earth's surface has not been there since the birth of the Earth. It has been continuously leaking out of the Earth's interior throughout the Earth's history. Even today, carbon from the Earth's interior continues to leak out through volcanoes. Some carbon may go back to the Earth's interior through subduction of oceanic plates. Our laboratory is quantitatively elucidating the global carbon cycle system. The key point is mantle wedge such as the one just below Japan. In peridotites, fluid inclusions composed mainly of carbon dioxide are found extensively. If the origin of such carbon materials can be identified, we may be able to bridge the missing link in the global carbon cycle system involving the Earth's interior. Our laboratory has been developing a Raman spectroscopic mass spectrometry method that enables nondestructive analysis of the isotopic composition of individual fluid inclusions. Now, light seems to be shining on the path to its natural application. What would you do if you realized that carbon on the Earth's surface would continue to increase in perpetuity?