eBook - ePub
Early Life on Earth
Evolution, Diversification, and Interactions
Kenichiro Sugitani
This is a test
Partager le livre
- 400 pages
- English
- ePUB (adapté aux mobiles)
- Disponible sur iOS et Android
eBook - ePub
Early Life on Earth
Evolution, Diversification, and Interactions
Kenichiro Sugitani
DĂ©tails du livre
Aperçu du livre
Table des matiĂšres
Citations
Ă propos de ce livre
This book comprehensively explores the early evolution of life and the Archean environment. Topics include the differences between prokaryotes and eukaryotes, variations in metabolisms, concepts of ecosystems and biogeochemical cycles (nitrogen, sulfur, phosphorous), Archean geology and environments, and the widely accepted early evolutionary history of life. The text addresses controversies regarding early life and its environment, particularly the unusual microfossil assemblages from the 3.4 Ga Strelley Pool Formation and the 3.0 Ga Farrel Quartzite of Western Australia. Readers will get a fuller picture of the Archean world, and an appreciation of many still unresolved questions.
Key Features
-
- Illustrated with figures visualizing ecosystems, biogeochemical cycles etc which are indispensable for understanding the Archean Earth.
-
- Includes tables arranging key words, definitions, and interpretations.
-
- Documents the Archean environment with photographic evidence and detailed descriptions the rocks, minerals and microfossils.
-
- Summarizes the latest field research.
-
- Details exciting unresolved questions for future study.
Foire aux questions
Comment puis-je résilier mon abonnement ?
Il vous suffit de vous rendre dans la section compte dans paramĂštres et de cliquer sur « RĂ©silier lâabonnement ». Câest aussi simple que cela ! Une fois que vous aurez rĂ©siliĂ© votre abonnement, il restera actif pour le reste de la pĂ©riode pour laquelle vous avez payĂ©. DĂ©couvrez-en plus ici.
Puis-je / comment puis-je télécharger des livres ?
Pour le moment, tous nos livres en format ePub adaptĂ©s aux mobiles peuvent ĂȘtre tĂ©lĂ©chargĂ©s via lâapplication. La plupart de nos PDF sont Ă©galement disponibles en tĂ©lĂ©chargement et les autres seront tĂ©lĂ©chargeables trĂšs prochainement. DĂ©couvrez-en plus ici.
Quelle est la différence entre les formules tarifaires ?
Les deux abonnements vous donnent un accĂšs complet Ă la bibliothĂšque et Ă toutes les fonctionnalitĂ©s de Perlego. Les seules diffĂ©rences sont les tarifs ainsi que la pĂ©riode dâabonnement : avec lâabonnement annuel, vous Ă©conomiserez environ 30 % par rapport Ă 12 mois dâabonnement mensuel.
Quâest-ce que Perlego ?
Nous sommes un service dâabonnement Ă des ouvrages universitaires en ligne, oĂč vous pouvez accĂ©der Ă toute une bibliothĂšque pour un prix infĂ©rieur Ă celui dâun seul livre par mois. Avec plus dâun million de livres sur plus de 1 000 sujets, nous avons ce quâil vous faut ! DĂ©couvrez-en plus ici.
Prenez-vous en charge la synthÚse vocale ?
Recherchez le symbole Ăcouter sur votre prochain livre pour voir si vous pouvez lâĂ©couter. Lâoutil Ăcouter lit le texte Ă haute voix pour vous, en surlignant le passage qui est en cours de lecture. Vous pouvez le mettre sur pause, lâaccĂ©lĂ©rer ou le ralentir. DĂ©couvrez-en plus ici.
Est-ce que Early Life on Earth est un PDF/ePUB en ligne ?
Oui, vous pouvez accĂ©der Ă Early Life on Earth par Kenichiro Sugitani en format PDF et/ou ePUB ainsi quâĂ dâautres livres populaires dans Biological Sciences et Microbiology. Nous disposons de plus dâun million dâouvrages Ă dĂ©couvrir dans notre catalogue.
Informations
1 Space, Solar System, and the Earth
DOI: 10.1201/9780367855208-1
1.1 Introduction
In this first chapter, the origins of elements in the universe, evolution of our solar system and the Earth, and the origins of the oceans and the atmosphere are reviewed. Based on âthe Big Bang theoryâ, our universe began 13.8 Ga ago, whereas our solar system had evolved around 4.6 Ga ago, which is assumed to be nearly identical to the age of the Earth (Figure 1.1). Our (not only human beings but also the other organisms) existence is inseparable from the universe, where elements have been generated through dynamic processes. Formation of our habitable planet is closely related to the evolution of the solar system. Habitability for âthe Earth-type lifeâ prerequisites the prolonged presence of water (H2O) and the preceding supply of building blocks of life. These topics are mentioned here.
1.2 Elements in the Universe and Their Origins
To date, 118 elements including synthetic ones have been identified, from 1H to synthetic 118Og (oganesson). Despite such diversity of elements, their abundance in the universe deduced from that of our solar system is extremely biased to elements with small atomic numbers (Figure 1.2). The elemental abundance of our solar system has been deduced based on spectroscopic analyses of the solar sphere for volatile elements and chemical compositions of chondrite for nonvolatile elements: chondrite is a sort of meteorite and is thought to have preserved primitive solid phase compositions of the solar system (see Column).
Hydrogen is the most abundant element in our solar system and the universe, and He is the next one. These two dominate more than 98% of all the elements. Elemental abundances exponentially decrease to elements with larger atomic numbers, with some irregularities represented by relative depletion of Li, Be, and B and by relative enrichment of Fe (Figure 1.2). The most important essential elements for life such as H, C, N, O, S, and P, comprising carbonhydrates, lipids, nucleic acids, and polyphosphates are major constituents.
Hydrogen, He, Li, and Be were produced soon after the beginning of the universe. In other words, the other elements were not present at that time. Some of the other elements have been produced by stepwise nuclear fusions inside fixed stars composed dominantly of H. The heaviest element produced by this process is Ti, and the size of a star (fixed star) gives constrains on what element is finally generated in its core. In the core of the Sun, four atoms of 1H are fused to produce one atom of 4He. Inside fixed stars larger than the Sun, heavier elements could be produced by further nuclear fusion. This process is followed by a process called neutron capture that could increase the mass number of an element, with an increase of atomic number to a lesser extent, eventually producing 56Fe. Elements heavier than 56Fe are produced also by neutron capture. However, this process occurs only during supernova explosion, which would occur at the end of fixed stars more than ca. 10 times heavier the Sun. This neutron capture process is called ârapid processâ, whereas the process of neutron capture inside fixed stars is called âslow processâ.
Associated with nuclear fissions, energy is produced and emitted to the space as the electromagnetic radiation from fixed stars. The Sun has solar radiation estimated to be 3.6 Ă 1026W. The Earth receives only 4.55 Ă 10â8 % of this radiation energy. The solar radiation is dominated by visible light (47%) (380â700 nm), ultraviolet (7%) (10â380 nm), and infrared (46%) (700 nmâ1 mm) {note that these ranges are somewhat ambiguous (https://photosyn.jp/pwiki/)}. Most photoautotrophic organisms (see Chapter 3) almost exclusively utilize visible light to produce organic matter (OM), and some algae can utilize near infrared (700â750 nm) (e.g., NĂŒrnberg et al., 2018). The terrestrial and the marine surface ecosystems are founded on this solar radiation energy.
1.3 Evolution of Our Solar System
Our solar system had evolved from molecular clouds composed of interstellar dusts and gases (interstellar matter). The interstellar matter was originated largely from previously existed stars and their planetary systems, scattered by for example supernova explosion. These wrecks were raw materials for our solar system and life on the Earth and if present, others. Elements produced directly by the Big Bang (Big Bang nucleosynthesis) were limited to light ones up to Be. Namely, our bodies and those of other organisms are composed largely of elements produced by nucleus syntheses within fixed stars and during their supernova explosions. Elements produced by the rapid process include Cu, Zn, and Mo, which are essential to many of the organisms on the Earth. These elements comprise reaction centers of several important enzymes such as superoxide dismutase, laccase, and nitrogenase.
Interstellar medium refers to interstellar matter and cosmic rays present between solar systems. The region with higher density of interstellar medium, compared with the surroundings, is called âinterstellar cloudâ. Molecular cloud refers to the region with a density of 104â106 H2 per cmâ3; the major component of molecular cloud is H2, although many of other molecules, including e.g., carbon monoxide (CO), H2O, ammonia (NH3), hydrogen cyanide (HCN), and formaldehyde (HCHO), have been detected. Recently, methylamine (CH3NH2), which is a precursor of glycine (C2H5NO2), the simplest amino acid, was recently detected (BĂžgelund et al., 2019). Within such a molecular cloud, fixed star forms. The fixed star formation is thought to be triggered by fragmentation of high-density area of the cloud (molecular cloud core) or by shock wave generated by, for example, supernova explosion. In the following, the assumed formation process of our solar system is briefly described.
Destruction of gravitational stability resulted in contraction and rotation of the molecular cloud, eventually forming the primordial sun and the surrounding disk (the primitive solar sytem nebula) composed of gases (mainly H2) and dusts (mainly H2O ice), with trace amounts of minerals and metals. The formation of this disk was associated with precipitation of dusts to the rotating surface, which released their potential energies. Released potential energy was transformed to thermal energy, which was higher in the region closer to the primitive sun. Obviously, the solar radiation was stronger in the region closer to the primitive sun. Temperature gradient in the primitive solar system expected from these two factors (potential energy of dusts and solar radiation) indicates that within the inner region closer to the primitive sun (~3 astronomical unit: AU), dusts were once entirely evaporated, except for materials with very high boiling points. Once vaporized, materials within the inner zone would subsequently condense to form minerals and metals.
The growth of planets is thought to have been a stepwise dynamic process. Namely, particles (dusts) once formed planetesimals, which had grown through collision coalescence with each other to protoplanets (100â1,000 km in diameter). Compositions of planetesimals were different depending on distance from the primodal sun (Figure 1.3). Planetesimals formed within the inner zone had rocky composition, whereas those in the outer zone had icy H2O composition, and protoplanets as well. Through further collision coalescence, protoplanets had grown to the primitive planets, direct precursors of the present planets. The planets had grown in the primary solar atmosphere mostly composed of H2 at least in their early stage of growth. As H2O was much more abundant compared with rocky materials in the solar system, icy primitive planets could have grown much larger than the rocky planets and captured the primary H2 atmosphere, resulting in the formation of gas giants such as Jupiter and Saturn. Uranus and Neptune are also gaseous and icy planets (ice giants), although their masses are much smaller than Jupiter and Saturn. One explanation for this is that their primitive planets had formed after the blow-off of the primary atmosphere by strong solar wind. This wind had completely removed the primary atmosphere surrounding the rocky planets, which was closely related to the origins of atmosphere and oceans of the Earth and Mars (e.g., Wurm, 2019 and reference therein).
1.4 Evolution of the Earth's Inner Structure
The Earth is characterized by a three-layered concentric structure composed of core, mantle, and crust. The core is composed dominantly of metallic Fe, with some light elements required. It is also divided into the inner solid core and the outer liquid core, which is predicted by analyses of seismic waves and the presence of dipole magnetic field of the Earth. Candidates for light elements contained in the core have been thought to be C, S, O, H, and Si. Recent studies emphasize H. One approach was made by estimation of temperature just above the core (the bottom of the solid mantle) (Nomura et al., 2014). The estimated temperature was much lower than that required for melting of pure metallic Fe. In order to explain this inconsistency, a large amount of H (0.6 weight %) should be contained in the outer core. The authors suggested the possibility that dissolution of H into metallic Fe had occurred within m...