Planet Earth, Past and Present, 1st ed. 2023
Parallels Between Our World and its Celestial Neighbors
Popular Astronomy Series

The Earth is not the world it once was, and it is not the world it will always be.  

This book describes the exciting, complex, and occasionally baffling history of our own planet. Over the course of its 4.5 billion years, Earth has undergone astonishing changes to its surface and atmosphere, at times more closely resembling other planets in our Solar System than the habitable, teeming biosphere of today. 

Introduction: The Earth today, and the alien worlds around it

1. Before Earth

o   Formation of the solar system: temperature and compositional gradients in the cloud

·       Lords of the rings, moons and waves

o   Views of extrasolar disks and what they tell us of our roots

·       Seeing our past through Hubble and Spitzer

o   The “snow line” and structure of the early Sun’s nebular cloud

o   Our solar system’s habitable zone

·       Habitable zones around other stars

o   Our place in the Milky Way galaxy

·       The galactic habitable zone

2. Earth=Mercury: Earth as a molten world

o   Terrestrial planets begin as molten balls of rock

§  Accretion and differentiation

§  Earth formation: cold or hot?

§  The importance of layers

§  The sky is falling: metallic vs stony asteroids, cometary ices

o   How Mercury and the Earth differ, solar influences

o   Shared heritage, the echoes of planet Mercury within the rocks of Earth

·        [news inset: newly discovered mineral inside a diamond hints at the nature of Earth’s deepest mantle]

3. Earth=Venus: Our planet as a Dante-esque oven

o   Ocean vs desert, and where the balance lies

o   Oceans condense from atmosphere

o   Earth before rust: land and sea without free oxygen

·        [news inset: Earth’s evil twin: why did Venus end up so different from Earth? Asteroid impacts may be the culprit]

o   New dawn for Venus: upcoming missions and what they may soon tell us

4. Earth and the Asteroid belt: the impact of an uneasy relationship during the great solar system cleanup

o   Are the asteroids a failed planet?

o   What the asteroids added to the Earth’s mix

§  Specific minerals, water, gases

o   Birth of the Moon.

§  Theia impact

o   The Moon’s importance for tides, axial stabilization, etc

o   The Earth/Jupiter relationship, a natural force-field

·        [news inset: missions to the asteroids: can we move the rocks?]

·        [news inset: what we’ve learned from Ryugu and Itokawa samples]

5. Earth=Titan

o   Titan as a chemical proxy for the early Earth (nitrogen and methane, a winning                                        combination?)

§  Titan’s methane as starting point for complex organics

§  Titan as a snapshot of Earth’s prebiotic chemistry

·       Earth evidence wiped out, but Titan’s is frozen for us to explore

§  Was the atmosphere of pre-biotic Earth reduced or oxidized?

§  Hydrogen cyanide and the “cyanosulfidic” pathway to life

§  Panspermia and its problems; cosmic dust and precursors to amino acids

§  Carbonaceous chondrites, comets, and how they relate to life

o   Earth as a nursery

§  Chemistry and energy in the beginnings of life

o   Earth’s oxygenating event and how biology sculpts a planetary environment

o   Titan as a primordial Earth analog

·       Reduced atmosphere; early Titan warmer and richer in oxygen, similar to                                                     Earth

·       Primary chemical composition and vertical profile of the atmosphere

·       Physical and chemical combinations (including thymine and cytosine                                                                           production at Titan)

·       Energy sources (sunlight, Saturn radiation, possible cryovolcanism)

·       Atmospheric greenhouse effects

§  Life’s building blocks?

·       Cell membranes from acrylonitrile

·       Photochemically produced organic chemistry, amino acids and tholins (Miller-                                            Urey and follow-on experiments)

·       Three places for water on Titan

·       Carbon-based life without accessible water

·       Ammonia instead of water: N chemistry and pseudo biochemistry

·       Where is the methane coming from?

§  Is life in the universe inevitable? Dinosaurs to protozoans, a rich menagerie

§  Future Titan: a new birthplace?

6. Earth=Mars: the “Snowball” or “Slushball” Earth

o   The past lives of Earth and Mars

§  Water, water everywhere, but not a drop to breathe: oxygen-poor watery                                                   environments of early Mars and Earth

§  The “lost” billion years of Earth geology

§  Making a snowball: balance between greenhouse effects and runaway freeze

·       The role of sea-ice dynamics, wind, etc

·       The role of the carbon cycle and volcanism

·       Escape from the ice palace: the blossoming of oceans and freeing of metals

·       Links to the Cambrian explosion?

§  Raptian group of Canadian Cordillera: glaciers sandwiched between limestone,                                        and other equatorial glacier evidence of snowball Earth

§  Earth’s oxygenating event and how biology sculpts a planetary environment

§  The progression of life and its effect on the environment

·        [news inset: dinosaurs may have gotten huge during a rainy era]

o   Martian glaciers and echoes of Earth

§  Orbital obliquity and past glaciation

§  Morraines, scour marks and hanging valleys

§  Rock glaciers, active even today?

·       Kasei Valles, western sides of Tharsis volcanoes (for example)

o   Compare to ocean moons: Europa, Ganymede, Enceladus, others

§  Why did the ocean moons not freeze solid? Tidal and radiogenic heating

o   Earth’s Moon and axial stability (Stromatolite evidence of Earth’s stable orbit)

7. Distant Earths: exoplanets with potential

o   What we’ve found (the statistics)

§  Worlds orbiting red dwarfs, and the dangers of flares

·        [news inset:Our own Sun’s flares in history]

o   Super-Earths, both oceanic and terrestrial

§  Eyeball Earths, giant Earths, Earths without land, the super-Earth wet exoplanets, and                              insights they give us

o   Moons in habitable zones (and the problem of orbiting a planet so close to a star)

8. Earth=Venus, part II: Future Earth

o   A return to Venus? The flip side of a snowball Earth

o   Climate change: rising temperatures, disappearing coastlines, extreme weather

o   The future of the Sun; stellar life-cycles

o   Mass exodus, but where to go?

§  Terraforming (warming Mars, cooling Venus)

§  Despite the many discoveries of Earth-sized worlds in habitable zones, there’s no                            place like home.

8A. Important terms

8b. Further reading

 8c. Glossary

Tells a broad, nontechnical story of Earth’s formation and evolution for lay readers

Features original artwork of Earth and other bodies in the Solar System

Reflects the latest research in exoplanet studies, astrobiology, planetary geology, and other fields