Program: (20 min with question/discussion time for each speaker)

Abstract:

Masafumi Kameya

Title:
"Elucidation of the evolution of central metabolism"

Abstract:
One of my research subjects was microbial metabolism, in which various kinds of cellular biomolecules are synthesized from inorganic compounds. I studied carbon and nitrogen central metabolism in a bacterium belonging to a deep branch in the evolutionary tree. This bacterium has the reductive tricarboxylic acid (RTCA) cycle, a characteristic metabolic pathway for carbon dioxide fixation. Unique features were also found in nitrogen metabolism of this bacterium, and the findings provide insight into the evolutionary process of the central metabolism. In order to elucidate the metabolic mechanism in primitive life and its evolutionary processes, now I am planning to reconstruct ancient forms of the RTCA cycle in ELSI.

Marine Lasbleis

Title:
"Deep Earth dynamics: an insight in the early thermal and chemical history of the Earth?"

Abstract:
The structure and dynamics of the deepest parts of the Earth are still partly unknown. Enormous progresses have been made, both on the description of the structure of the mantle and core and on the mechanisms and dynamics that lead to such a structure. However, the observations are more precise every year and new mysteries need to be solved.
During my PhD, I have studied the dynamics and evolution of the Earth's inner core. In the past few years, seismic studies of the Earth's core have tremendously improved our knowledge of its structure. The solid inner core presents heterogeneities at all scales, including radial, regional and hemispherical variations. But most of the physical properties of the inner core are known with large uncertainties (temperature, viscosity, crystal properties etc.). Even basic properties, such as the age of the inner core, are unknown. I have studied some of the possible dynamics for the Earth's inner core. The goal was to obtain some constrains on the inner core's properties by comparing dynamical models and seismic observations. We developed a regime diagram to compare the different published models of large scale dynamics of the inner core by calculating the instantaneous strain rate. We also developed a new model for the bottom of the liquid outer core, where anomalous P-wave vel!
ocities are detected by seismic studies. Considering that the freezing of the inner core occurs inside this layer, as iron snow fall, we obtain an iron-rich layer which is compatible with seismic observations.
During this JSPS Fellowship, I will develop a few examples of partial melting and freezing in the deep Earth, using two-phase flow dynamics and chemical fractionation, to obtain strong constraints on the chemical and thermal history of the Earth. Among the few examples, I would like to study the freezing of the inner core and of the early mantle.

Takuya Saito

Title:
"Secular change of seawater salinity through time"

Abstract:
The secular change of seawater salinity must have been one of the most critical factors to unravel the origin and evolution of life on the Earth. Metazoans cannot survive in seawater over 2SU (SU=salinity unit: present day seawater salinity is defined as 1SU) because of osmotic pressure with the cell. However, this topic has not fully understood yet, because there are methodological problems to collect samples to be analyzed. Recently, some studies have tried to estimate seawater composition during Archean and Proterozoic using fluid inclusions trapped in hydrothermal quartz from pillowed basalt, which is expected to erupt at mid-oceanic ridge in open sea. However, two problems are remained, one is that their estimations of salinity have highly varied from 1SU to 5SU. The other is that these previous studies leave probability of the fluid with no relation to seawater like as water in river and the salt lake.
Here, we tried to reveal secular change in seawater salinity by introducing the systematic analysis of fluid inclusions of hydrothermal quartz trapped as the relics of seawater, which originated from mid-oceanic ridges.
It is necessary to collect the quartz from MORB. Such rock samples can be obtained from accretionary complex preserved on land environment. Based on the huge accumulated information obtained from accretionary complexes by previous work of our group, we selected the best locality and collected hydrothermal quart samples for this study. We carried out microthermometric analysis using fluid inclusions in MORB at 3.2 Ga, 2.7 Ga, and 600 Ma.
The results showed ca. 2.5-4.5 SU seawater at 3.2 Ga, also ca. 2.5-4.5 SU at 2.7 Ga, and 1.0-1.5 SU at 600 Ma. Through this drastic change through time, the Earth could become to secure the environment as a cradle for Metazoan by Neoproterozoic.

Rehana Afrin

Title:
"Mineral Surface as a Cradle for Life"

Abstract:
Much attention is focused on the possible role of mineral surfaces as adsorptive spots for concentration of pre-biotic molecules. Some of the surfaces are even considered to be catalytically active accelerating oligomerization/polymerization of prebiotic simple organic molecules, e.g., amino acids and nucleotides. According to the lron-Sulfur World theory of Wachtershauser [1,2,3] the alkaline vents on the ocean bed expelling water of 50-100 degrees C and rich with iron-sulfide minerals would have been a cradle for the most primitive life form.
This work aims at verifying the role of iron sulfides, namely pyrite and mackinawite, as concentrators of amino acids and as catalysts of their polymerization reaction leading to the formation of 2D catalytic network. Scanning probe microscopic technique in collaboration with other surface science technology will provide us the critical knowledge on the interaction between iron sulfide minerals and pre-biotic molecules.
The following will be taken as consideration of this study:
1) Establish iron sulfide mineral surface as a preferred site for the creation of life by preferentially adsorbing small life molecules and assisting their polymerization leading to the formation of precursors of proteins and RNA/DNA. 2) Characterize pyrite (and other iron-sulfide) surface after treatment with simulated Hadean conditions for any improvement of the above phenomena and as a plausible platform for the development of 2D Hadean life 3) Study the possibility of extending 2D surface network to evolve into 3D cellular life form after detachment from the surface.
This research will provide convincing evidence for a selective catalytic reactivity of iron-sulfide surface that would have enabled creation of 2D Hadean life.
References:[1] Wachtershauser, G. (1988) Microbiol Rev 52, 452-84. [2] Wachtershauser, G. (1994) Proc Natl Acad Sci USA 91,4283‐7. [3] Martin, W. and Russell, M. J. (2007) Philos Trans R Soc Lond B Biol Sci 362, 1887-925.

Shintaro Azuma
"Rheological decoupling at the Venusian Moho"

The strength of planetary materials is a key control on planetary tectonics because temperature, pressure, stress, and chemical composition produce strong rheological layering. In next ELSI Assembly, I would like to talk about the strength profile and absence of plate tectonics in Venus. Plate tectonics is one of the most important mechanism for material and heat circulation in Earth, however it does not exist on Venus for unknown reasons. We conducted two-phase deformation experiments to verify the reason of absence of plate tectonics on Venus. Our deformation experiments show that mantle olivine is much stronger than crustal plagioclase under conditions corresponding to Venusian Moho (i.e. Venus has a large strength contrast between the crust and mantle at the Moho.). Consequently, this strength contrast may cause the mechanical decoupling between crust and mantle convection in Venus. Also, we conducted the two-dimensional simulations based on our experimental data to veri!
fy the effect of the strength contrast on the subduction process. These simulations show that strength contrast at the Moho prevents the motion of Venusian crust. This might be an important factor to explain the absence of plate tectonics on Venus.