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
12 - The Archean Eon and the Origin of Life: I. Properties of and Sites for Life
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
The close of the Hadean and opening of the so-called Archean eon is defined and characterized by the oldest whole rock samples found on Earth, 4.0 billion years old. At the opening of the Archean, Earth had an atmosphere, rich in carbon dioxide, with perhaps some nitrogen and methane but little molecular oxygen, and liquid water was stable on its surface. Mantle convection had begun producing oceanic basalts and continental-type granitic rocks. The rate of impacts of asteroidal and cometary fragments had decreased significantly. The Moon, formed from Earth at the end of accretion some half billion years before, could be seen in the terrestrial sky.
By 3.5 billion years ago, rocks were present that recorded definitive evidence for life; less definitive evidence exists back to almost 3.9 billion years. Layered formations in ancient limestones contain concentric spherical shapes, stacked hemispheres and flat sheets of calcium carbonates (calcite), and trapped silts. These stromatolites are best understood as the work of bacteria from 3.5 billion years ago, precipitating calcium carbonate in layers as one of the byproducts of primitive photosynthesis. If the interpretation is correct, life on Earth was present then and somewhat earlier as well, because such bacteria constitute already reasonably well-developed organisms.
It therefore appears that, as Earth settled down from the chaos of accretion, core formation, and impacts, life was able to exist on its surface (figure 12.1).
- Type
- Chapter
- Information
- EarthEvolution of a Habitable World, pp. 134 - 152Publisher: Cambridge University PressPrint publication year: 1998