Chapter 4: A Geological and Chemical Context for the Origins of Life on Early Earth PDF

ASTROBIOLOGY Volume 24, Supplement 1, 2024...

ASTROBIOLOGY Volume 24, Supplement 1, 2024 ª Mary Ann Liebert, Inc. DOI: 10.1089/ast.2021.0139 Open camera or QR reader and scan code to access this article and other resources online. Chapter 4: A Geological and Chemical Context for the Origins of Life on Early Earth Laura E. Rodriguez,1,2 Thiago Altair,3,4 Ninos Y. Hermis,1,5 Tony Z. Jia,6,7 Tyler P. Roche,8 Luke H. Steller,9 and Jessica M. Weber1 Downloaded by 103.4.220.252 from www.liebertpub.com at 09/26/24. For personal use only. Abstract Within the first billion years of Earth’s history, the planet transformed from a hot, barren, and inhospitable landscape to an environment conducive to the emergence and persistence of life. This chapter will review the state of knowledge concerning early Earth’s (Hadean/Eoarchean) geochemical environment, including the ori- gin and composition of the planet’s moon, crust, oceans, atmosphere, and organic content. It will also discuss abiotic geochemical cycling of the CHONPS elements and how these species could have been converted to biologically relevant building blocks, polymers, and chemical networks. Proposed environments for abiogenesis events are also described and evaluated. An understanding of the geochemical processes under which life may have emerged can better inform our assessment of the habitability of other worlds, the potential complexity that abiotic chemistry can achieve (which has implications for putative biosignatures), and the possibility for bioche- mistries that are vastly different from those on Earth. Key Words: Hadean—Archean—Prebiotic chemistry— Abiogenesis—Abiotic organic synthesis. Astrobiology 24, S-76–S-106. E vents following the formation of Earth around a young Sun (see Chapter 3) determined the chemical environments in which life may have originated. This chapter evolved on Hadean Earth and does not discuss in detail abi- otic chemistry that could be relevant for the formation of alternative life-forms distinct from our own (i.e., ‘‘weird describes the current understanding of the geochemical en- life’’ or ‘‘exotic life’’); for a review on this topic the authors vironment and mechanisms behind the transition of nonliving kindly direct readers to Chapter 9: Life as We Don’t Know It. materials to living matter (i.e., the origins of life or abio- Chapter 4.1 will review what we know regarding the geo- genesis). The focus of this chapter is the period during which chemical composition of early Earth’s crust (lithosphere), life likely originated: from the Hadean Eon (4.56–4.0 billion oceans (hydrosphere), and atmosphere. Next, Chapter 4.2 years ago [Ga]) up to the first era of the Archean Eon (4.0–2.5 describes how the chemical interactions at the interface of Ga) known as the Eoarchean (*4.0 to 3.6 Ga). The subse- each of these geospheres can generate energy, organic com- quent chapter in this series (Chapter 5) will review our un- pounds, molecular polymers, enantiomeric excess, and che- derstanding of the evolution of life throughout Earth’s mical networks. In Chapter 4.3 we will discuss geochemical history. It is important to note that this chapter is focused on scenarios conducive to processes predicted to have been understanding mechanisms for how Earth-like life could have important for the emergence of living systems. Finally, the 1 NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA. 2 Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA. (Current) 3 Institute of Chemistry of São Carlos, Universidade de São Paulo, São Carlos, Brazil. 4 Department of Chemistry, College of the Atlantic, Bar Harbor, Maine, USA. (Current) 5 Department of Physics and Space Sciences, University of Granada, Granada Spain. (Current). 6 Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, Japan. 7 Blue Marble Space Institute of Science, Seattle, Washington, USA. 8 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA. 9 Australian Centre for Astrobiology, and School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, Australia. S-76  CHAPTER 4: HADEAN GEOCHEMISTRY AND ORIGINS OF LIFE S-77 chapter will finish by describing the potential chemistry of remained intense 4.25–3.87 Ga (i.e., the Late Heavy Bom- the simplest system that we could feasibly describe as living bardment [LHB]) as evidenced by craters on the Moon, (see Chapter 2 for a discussion on defining ‘‘life’’) and how Mars, and Mercury (see Chapter 3.3.4). abiotic chemistry could transition to a functioning protocell The Moon has had a significant influence on the habit- (Chapter 4.4). ability of Earth. Without the Moon, Earth’s axial tilt could oscillate and reach up to 85 degrees (Laskar et al., 1993), 4.1. The Hadean Environment instead of the current 23.5 degrees. Thus, the Moon prevents extreme climate swings that would make it difficult for com- Earth began forming from the dust and gas of the solar plex life to evolve (i.e., the Rare Earth hypothesis; Ward and disc around the developing Sun 4.567 – 0.001 billion years Brownlee, 2000). Moreover, the Moon is also responsible ago (Ga) and continued to accrete over a period of *107– for Earth’s oceanic tides, and it effectively slows Earth’s 108 years (see review by Connelly et al., 2017). Following rotation through ‘‘tidal braking,’’ such that the length of the main phase of accretion, molten Earth began to differ- one Earth day increases over time. During the Hadean it is entiate, forming the core, mantle, and crustal layers by estimated that an Earth day was only *12–18 hours long around 4.53 Ga (see Chapter 3.4.3.1). This is generally taken (Williams, 2000; Lathe, 2004). The shorter day-night cycles to mark the beginning of the geological eon known as the and cycling of oceanic tides (