Field:
Earth Science/Environment
Session Topic:
Primitive Earth and Atmosphere
Chair:
George L. Hashimoto / Kobe University
The origin and early evolution of life is one of the most attracting topic for us, but the
question is still very open. It has been indicated that the first life appears on Earth at
around 4.0 billion years ago. However, the surface environment at around this
important period of Earth’s history is uncertain because geologic evidence is very
scarce.
Indeed, we have no solid idea about the condition where the first life was generated
and evolved. We encounter many difficulties when we try to solve the origin of life.
The surface environment of Earth must have a great influence on the origin and
early evolution of life. For example, results of the famous Miller-Urey experiment
demonstrated that amino acids were synthesized by electric sparks in a hypothesized
atmosphere. Subsequently, similar experiments established that the oxidation state of
the atmosphere controled the yields of the synthesis of organic matter greatly. A
reduced atmosphere, which contains reduced species such as CH4, NH3, H2, and CO,
allows efficient abiotic synthesis of organic compounds, but it is less efficient to
synthesize the organic matter in the atmosphere with less abundant of reduced
species. The chemical composition of early Earth’s atmosphere would be a key for
understanding the origin and early evolution of life.
Co-evolution of life and environment is apparently attractive topic. Can you magine
how different the earth has been with or without life? Earth’s present atmosphere
contains molecular oxygen, and the oxygen is ultimately derived from oxygenic
photosynthesis. Prior to emergence of photosynthesis, the atmosphere probably would
not contain molecular oxygen.
The modification of environment also affect the evolution of biota. The process of
oxygenation of the atmosphere might lead to drastic evolution of life, e.g., emergence
of multicellular life. This session invited two speakers who explore the environment of
ancient Earth by geological methods. The reconstruction of Earth’s environmental
conditions in the geologic past is a challenging task. First, we need to find a material
which preserves the record of ancient environment. It is difficult to find a pristine
sample, since Earth’s surface has been always renewed through geological processes,
such as volcanism and tectonic activity. Hence, we are often forced to analyze a very
tiny sample which is also often metamorphosed. However, the recent development in
the analysis techniques enables us to analyze even a microscopic and metamorphosed
sample with extremely high precision. Two speakers of this session will present their
results obtained by such a state-of-the-art analysis, and the Earth’s surface
environment at the time of interest would be discussed.