Life in the Universe

by Schulze-Makuch, Dirk; Irwin, Louis N.

• ISBN13: 9783540307082
• ISBN10: 3540307087
• Format: Paperback
• Copyright: 2006-03-18
• Publisher: Springer Verlag

Summary

Energy, chemistry, solvents, and habitats - the basic elements of living systems - define the opportunities and limitations for life on other worlds. This study examines each of these parameters in crucial depth and makes the argument that life forms we would recognize may be more common in our solar system than many assume. It also considers, however, exotic forms of life that would not have to rely on carbon as the basic chemical element, solar energy as the main energy source, or water as the primary solvent. Finally the question of detecting bio- and geosignature of such life forms is discussed, ranging from earth environments to deep space. While speculative considerations in this emerging field of science cannot be avoided, the authors have tried to present their study with the breadth and seriousness that a scientific approach to this issue requires. They seek an operational definition of life and investigate the realm of possibilities that nature offers to realize this very special state of matter and avoid scientific jargon wherever possible to make this intrinsically interdisciplinary subject understandable to a broad range of readers.

Table of Contents

Introduction	1	(6)
Definition of Life	7	(28)
Problems with Common Assumptions about the Nature of Life	7	(6)
Modern Definitions of Life	13	(1)
Our Definition of Life	14	(5)
Bounded Microenvironments in Thermodynamic Disequilibrium	14	(2)
Transformation of Energy and Environment to Maintain a Low Entropy State	16	(2)
Information Encoding and Transmission	18	(1)
Implications for the Origin of Life	19	(8)
Inferences for the First Cellular Membranes	19	(2)
Inferences with Regard to the First Metabolism	21	(2)
Inferences for the First Replication Mechanism	23	(1)
Other Inferences	24	(1)
Size	24	(1)
Type of Medium	25	(1)
Environmental Conditions	26	(1)
Implications for the Remote Detection of Life	27	(1)
Chapter Summary	28	(7)
References	29	(6)
Lessons from the History of Life	35	(14)
A Brief History of Life on Earth	35	(2)
Lessons from the History of Life on Earth	37	(7)
Life Arises Relatively Quickly under Conducive Conditions	37	(1)
Life Tends to Stay Small and Simple	38	(1)
Most Organisms Remain Relatively Unchanged over their Evolutionary Life Spans	39	(1)
Evolution is Accelerated by Environmental Changes	40	(2)
Complexity Inevitably Increases but as the Exception rather than the Rule	42	(1)
Biodiversity is Promoted by Heterogeneous Environments	43	(1)
Individuals are Fragile, but Life is Hardy	44	(1)
Questions Unanswered by the History of Life on Earth	44	(2)
Chapter Summary	46	(3)
References	46	(3)
Energy Sources and Life	49	(28)
Life As We Know It	49	(3)
Oxidation-Reduction Chemistry as an Energy Source for Life	49	(3)
Light as an Energy Source for Life	52	(1)
Life Unknown to Us	52	(17)
Electromagnetic Waves (other than Visible Light)	53	(1)
Thermal Heat Capacity	54	(3)
Kinetic Energy	57	(1)
Osmotic or Ionic Gradients	58	(3)
Magnetic Fields as Energy Source for Life	61	(1)
Possible Biogenic Use of the Lorentz Force	62	(2)
Possible Biogenic Use of Induction	64	(1)
Concluding Remarks on the Biogenic Use of Magnetic Energy	65	(1)
Gravitational Forces	65	(1)
Tectonic Stress	66	(1)
Pressure Gradients	66	(1)
Spin Configurations	67	(2)
Radioactivity	69	(1)
The Question of Entropy, Uniformity, and Origin	69	(2)
Survey of Energy Sources in our Solar System	71	(1)
Chapter Summary	71	(6)
References	74	(3)
Building Blocks of Life	77	(24)
The Uniqueness of Carbon	77	(4)
Alternatives to Carbon as the Universal Building Block of Life	81	(1)
The Possibility of Silicon-Based Life	82	(11)
Physical Properties of Silicon	82	(2)
Role of Silicon for Terrestrial Life	84	(3)
Polymeric Chemistry of Silicon	87	(2)
Environmental Conditions for the Possibility of Silicon-based Life	89	(1)
Life Based on Silane?	89	(2)
Life Based on Silicone?	91	(1)
Life Based on Silicate?	92	(1)
Other Alternatives as the Universal Building Block of Life	93	(2)
Chapter Summary	95	(6)
References	96	(5)
Life and the Need for a Solvent	101	(22)
Water as the Universal Solvent for Life on Earth	102	(5)
Other Polar Solvents as Alternatives to Water	107	(7)
Ammonia	108	(2)
Hydrocyanic Acid	110	(2)
Hydrofluoric Acid	112	(1)
Hydrogen Sulfide and Sulfur Dioxide	112	(1)
Methyl Alcohol (Methanol)	113	(1)
Hydrazine	113	(1)
Non-Polar Solvents as Alternatives to Water	114	(2)
Quantitative Assessment of Solvent Candidates	116	(2)
Some Additional Thoughts	118	(1)
Chapter Summary	119	(4)
References	120	(3)
Habitats of Life	123	(18)
Life on the Surface	123	(1)
Life Beneath the Surface	124	(4)
Life in the Atmosphere	128	(4)
Life in the Space Environment	132	(2)
Chapter Summary	134	(7)
References	135	(6)
Ideas of Exotic Forms of Life	141	(8)
Life Based on Spin Configurations	141	(2)
Fred Hoyle's Black Cloud and Similar Ideas	143	(1)
Life on a Neutron Star	143	(1)
Life on a Brown Dwarf	144	(1)
Some Other Ideas on Forms of Exotic Life	145	(1)
Chapter Summary	145	(4)
References	146	(3)
Signatures of Life and the Question of Detection	149	(18)
Biosignatures and Geosignatures of Life	149	(6)
Atmospheric Composition of a Planetary Body	150	(1)
Geological Evidence	151	(1)
Fossil Evidence	152	(1)
Macromolecules and Chirality	153	(1)
Presence of Metabolic By-Products and End-Products	153	(1)
Production of Biogenic Heat	154	(1)
Signatures of More Advanced Life	154	(1)
Geoindicators of Life	155	(6)
Presence of an Atmosphere or Ice Shield	156	(1)
Internal Differentiation	156	(1)
Polymeric Chemistry	157	(1)
Energy Source	157	(3)
Liquid Medium as a Solvent	160	(1)
Geoindicators for Life in our Solar System	161	(1)
Extrasolar Planetary Detection	162	(5)
Chapter Summary	167	(1)
References	167