Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- PART ONE THE ASTRONOMICAL PLANET: EARTH'S PLACE IN THE COSMOS
- PART TWO THE MEASURABLE PLANET: TOOLS TO DISCERN THE HISTORY OF EARTH AND THE PLANETS
- PART THREE THE HISTORICAL PLANET: EARTH AND SOLAR SYSTEM THROUGH TIME
- 10 Formation of the Solar System
- 11 The Hadean Earth
- 12 The Archean Eon and the Origin of Life: I. Properties of and Sites for Life
- 13 The Archean Eon and the Origin of Life: II. Mechanisms
- 14 The First Greenhouse Crisis: The Faint Early Sun
- 15 Climate Histories of Mars and Venus, and the Habitability of Planets
- 16 Earth in Transition: From the Archean to the Proterozoic
- 17 The Oxygen Revolution
- 18 The Phanerozoic: Flowering and Extinction of Complex Life
- 19 Climate Change Across the Phanerozoic
- 20 Toward the Age of Humankind
- PART FOUR THE ONCE AND FUTURE PLANET
- Index
- Plate section
15 - Climate Histories of Mars and Venus, and the Habitability of Planets
from PART THREE - THE HISTORICAL PLANET: EARTH AND SOLAR SYSTEM THROUGH TIME
- Frontmatter
- Contents
- Preface
- Acknowledgments
- PART ONE THE ASTRONOMICAL PLANET: EARTH'S PLACE IN THE COSMOS
- PART TWO THE MEASURABLE PLANET: TOOLS TO DISCERN THE HISTORY OF EARTH AND THE PLANETS
- PART THREE THE HISTORICAL PLANET: EARTH AND SOLAR SYSTEM THROUGH TIME
- 10 Formation of the Solar System
- 11 The Hadean Earth
- 12 The Archean Eon and the Origin of Life: I. Properties of and Sites for Life
- 13 The Archean Eon and the Origin of Life: II. Mechanisms
- 14 The First Greenhouse Crisis: The Faint Early Sun
- 15 Climate Histories of Mars and Venus, and the Habitability of Planets
- 16 Earth in Transition: From the Archean to the Proterozoic
- 17 The Oxygen Revolution
- 18 The Phanerozoic: Flowering and Extinction of Complex Life
- 19 Climate Change Across the Phanerozoic
- 20 Toward the Age of Humankind
- PART FOUR THE ONCE AND FUTURE PLANET
- Index
- Plate section
Summary
INTRODUCTION
Earth at the close of the Archean, 2.5 billion years ago, was a world in which life had arisen and plate tectonics dominated, the evolution of the crust and the recycling of volatiles. Yet oxygen (O2) still was not prevalent in the atmosphere, which was richer in CO2 than at present. In this last respect, Earth's atmosphere was somewhat like that of its neighbors, Mars and Venus, which today retain this more primitive kind of atmosphere.
Speculations on the nature of Mars and Venus were, prior to the space program, heavily influenced by Earthcentered biases and the poor quality of telescopic observations (figure 15.1). Thirty years of U.S. and Soviet robotic missions to these two bodies changed that thinking drastically. The overall evolutions of Mars and Venus have been quite different from that of Earth, and very different from each other. The ability of the environment of a planet to veer in a completely different direction from that of its neighbors was not readily appreciated until the eternally hot greenhouse of Venus' surface and the cold desolation of the Martian climate were revealed by spacecraft instruments.
However, robotic missions also revealed evidence that Mars once had liquid water flowing on its surface. It is tempting, then, to assume that the early Martian climate was much warmer than it is at present, warm enough perhaps to initiate life on the surface of Mars.
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- EarthEvolution of a Habitable World, pp. 177 - 195Publisher: Cambridge University PressPrint publication year: 1998