Study Guide for Origins of Earth and LifeOrigins of Earth and LifeThis is the first book of the Course and there are two accompanying video programmes. The book is assessed in TMA 01. (Note that there are self-assessment questions in the Multiple Choice Question Booklet. You should complete these as you study the text and they will also be useful for revision of the Course.) Your study of the Course begins with reading this book. Chapter 1 What is life? This short chapter is about definitions and it introduces you to the central role of carbon and its compounds in all known life-forms on Earth, and probably of all other life-forms (if there are any) in the Universe. Chapter 2 Stars and alchemy, planets and life Life cannot become established anywhere in the Universe without some form of planetary body to colonize. Temperature and pressure conditions at the surface of that body almost certainly have to be such as to enable liquid water to exist. This chapter reviews the evidence of how the Universe came into being (at the Big Bang), and how all the chemical elements were synthesized from primordial hydrogen formed at that moment of creation. It also describes the formation of galaxies, stellar systems and planets, including our own Solar System. The chapter ends at formation of the early Earth, some 4.6 billion years ago. Chapter 3 The early Earth – conditions for life? When it was first formed, the Earth was very different from what it is now: probably hotter and without free (molecular) oxygen in an atmosphere dominated by nitrogen and carbon dioxide. The Moon formed at this early stage, and all the planets of the early Solar System were subjected to intense meteorite bombardment. There is good geological evidence that life became established on Earth as long ago as 3.8 billion years, in a very primitive form, possibly similar to the putative ancient life-forms reportedly discovered on Mars in the mid-1990s. The chapter ends by considering the nature of the environment to which the first organisms on Earth must of necessity have been adapted. Chapter 4 The window of opportunity The questions of how life originated and in what particular environmental niche, remain subjects of continued discussion and research to this day. Ancient and modern theories are reviewed, and the evidence examined. Life could not have survived without the self- replicating mechanism (the genetic code) embodied in the DNA molecule, and part of the chapter is concerned with how self-replication might have evolved with the earliest organisms. The evidence for ancient life-forms on Mars is also examined, in the context of the question: did life originate on Earth or was it perhaps ‘imported’ from elsewhere? The final sections of the chapter consider the still unresolved issue of just when it was that the atmosphere became sufficiently rich in oxygen to support aerobic respiration that characterizes most animal life on Earth today. Required background and the most difficult sections If you have studied Discovering Science (S103) (or its predecessor, S102), you should have little difficulty with any of this material. It will be useful to have some understanding of: •basic physical concepts including pressure, temperature, density and changes of state; of atomic structure (including isotopes); •the use of symbols and equations to describe chemical elements and compounds (including the principal carbon compounds essential for life); •simple chemical reactions; •simple mathematical equations; •basic processes such as photosynthesis and respiration, oxidation and reduction, conduction and convection, and plate tectonics. Chapters 2 and 4 are probably the most difficult in general, and especially if you have little or no background of chemistry and/or biology. Finally: (a)You are required to understand but NOT to memorize the definitions of terms (you will be sent a Glossary for that), nor any formulae or numbers. (b)This book (or indeed in the Course as a whole), does not contain any complicated mathematics. You are required only to be basically numerate, i.e. able to do simple addition, subtraction, multiplication and division, and occasionally to rearrange a simple formula. Video programmes Video Band 1: ‘The Nature of Impacts and their Impacts on Nature’ This video programme considers the impact of asteroids and comets with the Earth and the effects that such impacts have had on the Earth’s environment. You should watch this programme after you have read Chapter 3 of Origins of Earth and Life. Please refer to the Video Notes for a summary of the programme contents. Video Band 2: ‘The K–T Event’ This video programme focuses on a single impact event which resulted in the 180km Chicxulub crater on the Yucatan peninsula of Mexico. Links between this impact and Cretaceous–Tertiary mass extinctions are also discussed. You should view this programme after you have completed studying this book and again after studying the next book of the Course, Evolving Life and the Earth , where the K–T boundary discussion continues. Please refer to the Video Notes for further details. This book necessarily focuses on the physical and chemical conditions that lead to the existence of life on Earth, and underpins the later books. If your leanings are more towards Biology or Earth Sciences, you may find it demanding, and not what you expected of an Earth and Life Course. Don’t worry – you will find that later books in the Course have a quite different balance, which should be more to your liking. Website Read the following sections on the S269 website: Origins of Earth and Life – Topics TMAs Course News Other Resources Supplementary Materials Copyright © 2003 The Open University SUP 74298 9 Back to S269 |