When Eden Comes to Titan


donald_brownleeDonald Brownlee, co-author of "Rare Earth," "The Life and Death of Planet Earth", and Professor of Astronomy of the University of Washington in Seattle.

peter_wardPeter Ward, co-author of "Rare Earth," "The Life and Death of Planet Earth", and Professor of Geological Sciences at the University of Washington in Seattle

Paleontologist Peter D. Ward and astronomer Donald Brownlee of the University of Washington, recently published their insights into the future of the planet. The excerpted sections from their new book "The Life and Death of Planet Earth", poetically portrays a very fragile future – one profoundly grounded by what we now know so far about the distant past.

The predictable rhythm of this terrestrial lifecycle comes in stages: glaciers, supercontinents, loss of plants, then animals, and boiling oceans towards what might look like present day Venus. The final stage of life on Earth features the last gasp of a Sun fusing its very heavy elements and forming a much expanded Red Giant star.

Excerpted from The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World

For millenia travelers have left graffiti to note their passage. Lewis and Clark and Daniel Boone carved their names on trees. The pharaohs left the Pyramids. Paleolithic man left magnificent charcoal drawings in Pyrenees caves. Mountaineers leave notes at the top of the peaks they conquer. World War II GI’s left "Kilroy was here" scrawls, and the Apollo astronauts left plaques and flags on the Moon. What can we leave behind on an Earth that is going to be vaporized, its atoms hurled into space? …When the Lunar Prospector mission crash-landed on the Moon in 1999, it carried with it the ashes of planetary scientist Gene Shoemaker. He became the first-known organism to have permanently escaped the surly bonds of Earth. He is quite literally the man on the Moon.

Each of us humans is one of some 6 billion humans currently alive, one of the numerous humans that have existed on Earth since the formation of our species during the Pleistocene epoch. In an analogous fashion, our planet Earth is one of an even greater population, one planet among the billions in the galaxy and untold billions and billions in the Universe….

Star field
In a universe brimming with stars, it is difficult to imagine that life exists nowhere else. "The countless worlds in the universe are no worse and no less inhabited than our Earth." Thus the Italian philosopher-scientist Giordano Bruno articulated a vision for astrobiology (De L’infinito Universo e Mondi, 1584). Credit:NASA/STScI/ESA

Many astrobiologists have concluded that the formation of microbial life on a planet within a habitable zone might be releatively easy–that, given the conditions of a liquid water-covered surface, many or most planets might yield life of some sort. If so, then millions of to hundreds of millions of planets in the galaxy have potential for advanced life. However, getting from microbial life to advanced life requires time and a stability of conditions. Only under such circumstances of long-term planetary stability where large-scale temperature fluctuations do not take place can the jump to the more fragile forms of complex life take place…

Perhaps complex life can occur on any planet where life evolves (or upon which it arrives) that also bears freestanding liquid water or some equivalent solvent.

One of the Earth’s most basic life-supporting attributes is its location, its seemingly ideal distance from the Sun. In any planetary system, there are regions–distances from the central star–where the Earth could survive with a surface environment similar to its present state. That is the habitable zone, the region in a planetary system where habitable Earth clones might exist…Our closest neighbors in space provide sobering examples of what happens to planets inside of, or outside of, the habitable zone. Interior to the habitable zone, a planet gets too hot. Venus is an example where this has happened. The surface of Venus is nearly hot enough to glow. If it ever had an ocean, it has evaporated and been totally lost to space.

Outside of the habitable zone, temperatures are too low. Mars is outside the habitable zone, and is frozen to depths of many kilometers below its surface.

Life is a very complex and delicate chemical balancing act, easily destroyed by too much heat or cold–and too many gamma rays, X rays, and other types of ionizing radiation….

Important attributes of our planet are its size, its radioactive heat, and the presence of a large metal core. All appear necessary to produce animal life: the metal core produces a magnetic field that protects the surface of the planet from radiation from space, while the radioactive material maintains the engine of plate tectonics, also, in our view, necessary for maintaining animal life on the planet.

The gas giants in our solar system. From left: Neptune, Uranus, Saturn, and Jupiter.
Credit: NASA

[Consider: ] It is the year 7 billion A.D. the Sun has gone into its red giant phase. The Earth has been consumed by the outer envelope of the 100-million-mile diameter sun. Mars is a dried and lifeless body with a surface temperature sufficient to melt its crustal rocks. Jupiter is a roiling heated mass rapidly losing gas and material to space. The ice cover of Jupiter’s moon Europa has long since melted away, followed by the disappearance of its oceans to space. Farther away, Saturn has lost its icy rings. But one world of this vast solar system has benefited from the gigantic red orb that is the Sun. It is Saturn’s largest moon, aptly named Titan.

Long before, in the time of humanity, a science fiction named Arthur C. Clarke penned a series of tales about the moon of Jupiter named Europa. In these stories, alien beings somehow truned Jupiter into a small but blazing star, and in doing so warmed Europa–and brought about the creation of life. A wonderful, though physically impossible, fable. Now in these late days of the solar system, the huge red Sun was doing the same to Titan, changing it from frozen to thawed, and in doing so liberating the stuff of life. But Titan was always a very different world than Europa. Like Europa, Titan always had oceans, frozen, to be sure, but oceans nevertheless. But where Europan oceans were water, those of Titan were of a vastly different substance–ethane. Titan had always been covered with a rich but cold stew of organic materials And with the coming of heat, for the first time Eden came to Titan. Like a baby born to an impossibly old woman, life came to this far outpost, the last life ever to be evolved in the solar system.

The red giant phase was short-lived–only several hundred million years, in fact. But it was enough. For a short time, for the last time, life blossomed in the solar system. After death, once more came the resurrection of life in masses of tiny bacteria like bodies on a moon once far from a habitable planet called Earth, a place that, in its late age, evolved a species with enough intelligence to predict the future, and be able to prophesize how the world would end….

Reprinted with permission. Copyright Peter D. Ward and Donald Brownlee. The coauthors also published the acclaimed and bestselling Rare Earth. Don Brownlee is a professor of astronomy at the University of Washington and has been involved in many space experiments; currently he is leading NASA’s Stardust mission to collect samples of a comet and return them to Earth. Peter Ward is a professor of geological science and zoology at the University of Washington and the author of nine other books, including Future Evolution, In Search of Nautilus, The Call of Distant Mammoths, and The End of Evolution, which was a finalist for the Los Angeles Times Book Prize.

Related Web Pages

Rare Earth Debate Series
Interactive Presentation: The Life and Death of Planet Earth
Tree of Life
Eukaryotic Origins
The Tree of Life Web Project