More from THE LIFE AND DEATH OF PLANET EARTH, mit comments by M.E.
. . . Earth did not spring into being in its present state; instead, it took billions of years to develop into what it is today. Similarly, it will not sustain today’s environment forever; Our planet will break down as the human body does, in a complex series of processes that can be forecast as surely as our own deaths. [We believe habitable planets die] slowly, over time, with the more complex parts going first, leaving behind ever-simpler fractions of life.
. . . First higher life is removed, ecosystem by ecosystem, as our planet dies. Left are ever-simpler microbial communities. Eventually even these will be seared out of existence by the crematorium that will be the inner solar system of an aging and expanding Sun. [Or, assuming that the Solar System doesn’t get lucky and get kicked out of the galaxy entirely, instead, will be blasted out of existence in the colossal explosions resulting from the merger of the Milky Way with the Andromeda Galaxy about 3 billion years from now - 2 billion years sooner than the Sun’s predicted departure from the Main Sequence and expansion into its red giant phase. See, e.g., http://www.galaxydynamics.org/tflops.html, http://www.cita.utoronto.ca/~dubinski/cv.pdf, http://www.haydenplanetarium.org/resources/ava/galaxies/G0601andmilwy, http://www.sdsc.edu/pub/envision/v16.1/hernquist.html, http://www.youtube.com/watch?v=OxtsUNA1tk8, http://antwrp.gsfc.nasa.gov/apod/ap080506.html, http://antwrp.gsfc.nasa.gov/apod/ap021128.html, http://antwrp.gsfc.nasa.gov/apod/ap090618.html, http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search, etc. for more on which. - Monty Eisenstein]
Is the history of the Earth analogous to that of the human body? Is the Earth “alive” in the way an organism is alive?
We certainly know that Earth has changed through time. If we could watch pictures of our planet at 500-million-year intervals, we would see a gradual change from a hot, molten world to one with oceans and atmosphere. Life, as we have seen - and will see in more detail as this book progresses - was part of this transformation. So is Earth similar to [humans], with a birth, life span, and impending death?
There is a hypothesis that supposes that our planet (and others as well in the galaxy and Universe) is, in fact, alive. In a series of books published in the 1970s and 1980s, a British scientist named James Lovelock argued that Earth is a living organism, even renaming our planet Gaia, for the Greek goddess who drew the living world from chaos. He argued that the interplay of air, water, rock, and organisms that create oxygen and store carbon resembles the biological system of a body, and that the Earth’s peculiar balance would be recognizable by any interstellar visitor as the product of life. Lovelock wrote:
Just as the shell is part of the snail, so the rocks, the air and the oceans are part of Gaia. Gaia, as we shall see, has continuity with the past back to the origins of life, and in the future as long as life persists. . . .
You may find it hard to swallow the notion that anything as large and apparently inanimate as the Earth is alive. Surely, you may say, the Earth is almost wholly rock, and nearly all incandescent with heat. The difficulty can be lessened if you let the image of a giant redwood tree enter your mind. The tree is undoubtedly alive, yet 99 percent of it is dead. The great tree is an ancient spire pf dead wood, made of lignin and cellulose by the ancestors of the thin layer of living cells which constitute its bark. How like the Earth, and more so when we realize that many of the atoms of the rocks far down into the magma were once part of the ancestral life of which we have all come. [Actually, not a bad analogy to Gaia. Think of Gaia is a huge, spheroidal plant which, rather than being rooted in the ground, is kept to a stable orbit around the Sun by the inorganic, insentient law of gravity. Gaia eats light and the minerals in the body of the planet, excretes infrared light (heat), and produces structures within herself that include individual organisms as we normally think of them as well as oceans, the atmosphere, soil, and her other constituents. Also, it helps to understand that Gaia is Earth’s biosphere, which does not constitute the entirety of the planet, but only those parts of it that are living creatures or parts of living creatures. The rest is equivalent to the food stored in a fertilized egg or seed, which the developing embryo progressively consumes over the period of its gestation. Gaia is not a planet-sized plant, but rather a film on the surface of our world that goes no deeper than a few hundred kilometers down into the subsurface regions, i.e., the Deep Hot Biosphere, assuming it exists, no higher than the lower levels of our atmosphere, and includes the creatures of land, sea, air, and subsurface in between. Could Gaia eventually run out of food, or some important nutrient? Yes, if we consider organic portions of her diet; but at no time soon if we consider only the continuously recycled minerals of the Earth, since most of these are radiologically stable and are not ultimately lost to life. - Monty Eisenstein]
Lovelock’s conviction that the Earth is actually a living organism has been embraced by some in the environmental and New Age movements, but it remains unaccepted by most scientists - including us - because the Earth as a whole doesn’t reproduce, metabolize, and evolve (although parts of it do all three). [Let’s hold off a while on whether Earth reproduces or not, at least long enough to find out whether Homo sapiens ever manages to make a permanent home for itself and other Earthly life on other worlds or not. - Monty Eisenstein] Organisms need both energy and new physical material to grow, and while Earth constantly receives energy from sunlight, it (except for a small contribution of new meteorites) simply recycles the material that is already present.
However, the recognition that specific properties of the Earth that are required to maintain life are both self-regulating, and changing, is scientific fact. There are highly complex “life support systems” that sustain atmospheric compositions and pressure, planetary temperature, and even surface land features that are quite different from those of a lifeless planet. Accordingly, a new scientific discipline called Earth System Science has resulted from the original musings of James Lovelock. It is one of the main reasons that we have the temerity to suggest that the various ends of the world are indeed predictable.
As an example, consider Earth’s remarkably stable temperature. We will explain in more detail why our Sun is getting hotter, but for now remember that its brightness has increased 30 percent since the creation of our planet. Venus, a hellish planet with a surface temperature sufficient to melt lead, gets 50 percent more solar radiation than our planet because it is closer to the Sun. Why hasn’t Earth become a nightmarish Venus? What sets the planetary thermostat that allows water to remain between the freezing and boiling points, thus allowing life?
The answer is three cycles: plate tectonics, the carbon cycle, and the carbonate silicate cycle, or the weathering of stone. We must understand how these operate now to understand what will happen to our planet in the future.
- Peter D. Ward and Donald Brownlee, The Life and Death of Planet Earth: How the New Science of Astrobiology charts the Ultimate Fate of Our World (Times Books, 2002; ISBN 978-0805075120; http://www.amazon.com/Life-Death-Planet-Earth-Astrobiology/dp/0805075127, pp. 51-54