Metamorphism of primitive organic molecules in the early Earth and implications for the origins of prebiotic molecules.

点击翻译按钮获取中文摘要

The formation of the Earth's biosphere is a fundamental yet very poorly understood problem. Since the early experiments of Urey, which captured the imagination of a generation, many researches have tried to develop models that can describe how simple organic molecules could have attained the complexity observed in even the simplest form of living organisms. Currently there is no model that can adequately describe a genetic pathway from simple primitive organic molecules (those containing elements H, C, O, N, and P) and the complex molecules (amino acids, RNA, etc) required for life. However, what has become clear recently is that organic molecules, and indeed life itself, are much more resistant to 'extreme' conditions than ever imagined (i.e. extreme cold, high temperatures and even high pressures). The purpose of the research described here is to determine whether high pressures and temperatures, such as those commonly achieved in the uppermost strata of the Earth's crust, can possibly have contributed in an important way in organizing primitive organic molecules into more complex and possibly prebiotic molecules. Primitive organic materials were delivered to Earth in mass quantities during the earliest time period of Earth called the Hadean Era, which extended from the accretion of proto-Earth (4.5 Gya) to the end of the Late Heavy Bombardment (3.85 Gya). During this era, these organic materials may have been subjected to metamorphic pressure-temperature conditions as a consequence of repeated impact-induced shock events as well as possible burial or subduction of organic material in Earth's interior. Our recent experiments on simple organic acids have shown that at metamorphic pressures and temperatures (0.5-10 GPa and 300-1000 K) new complex or polymerized organic compounds can form. Complex organic molecules are a prerequisite for the initiation of pre-biotic organic synthesis and possibly provide the material required for the emergence of Earth's biosphere. The objective of the research proposed here is to investigate the survivability, phase relations and decomposition chemistry of primitive organic molecules delivered to Earth at metamorphic pressures and temperatures and to investigate their reactivity with hydrous silicate materials. We propose experiments to determine the phase relations and decomposition chemistry of primitive organic materials found in interplanetary dust particles (IDP) and micrometeorites by directly observing their chemical behavior while at high pressure and temperature. Structural information will be obtained as necessary using synchrotron x-ray diffraction. In the second phase of experiments we will add either single crystal clay minerals or IDP directly to the organic starting material of interest. High-pressure-temperature experiments are made in externally heated diamond anvil cells at the University of Bristol using their compatible Raman and FTIR spectrometers. Diffraction data will be collected at the Diamond Light Source and the Advanced Light Source. The results of these experiments will allow us to accurately assess the contribution of primordial organic molecules to the origin of Earth's biosphere and atmosphere.