Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
Review Article
ABEL Model of the Two-step Formation of the Earth and the Significance of ABEL Bombardment to Produce a Habitable Planet
Shigenori MARUYAMAToshikazu EBISUZAKIYoshinori TANGE
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2018 Volume 127 Issue 5 Pages 647-682

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Abstract

 In the recently proposed ABEL model, the Earth was born as a dry planet without atmosphere and ocean components at 4.56 Ga. From 4.37 to 4.20 Ga, bio-elements, such as carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), were secondarily accreted on the Earth. This two-step formation model of the Earth is referred to as the advent of the bio-elements model (ABEL Model) and the event of the advent of bio-elements (water component) is referred to as ABEL Bombardment. It is evident that the solid Earth originated from enstatite chondrite-like dry material because of its oxygen isotopic composition and similar isotopes. On the other hand, the Earth's water originated primarily from carbonaceous chondrite material based on the hydrogen isotopic ratio. The ABEL model successfully explains this enigma between solid Earth and water. In addition, the importance of the secondary accretion of oxidizing bio-elements should be emphasized because this event became a precursor to initiating the metabolism for life to emerge on a highly reductive planet. If ABEL Bombardment had not occurred, life would never have emerged on the Earth. Therefore, ABEL Bombardment was one of the most important events for this planet to evolve into a habitable planet. Moreover, ABEL Bombardment is thought to be the trigger to switch from stagnant lid tectonics to plate tectonics on this planet because of the injection of volatiles into the initial dry Earth.

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