How Cyanobacteria Moved The Moon

On page 163 of the first hardback edition of David Waltham's "Lucky Planet", he says the Moon's distance cannot be the result of biological feedback, "there are no mechanisms to move the Moon".

Actually, there is a surprising mechanism, which I discussed with Lynn Margulis when she lectured in Portland, Oregon, years ago. She told us how cyanobacteria created oxygen, which cooled the earth and created ozone, shielding atmospheric water vapor from solar UV, greatly reducing hydrogen losses into space. She said (IIRC) that our deep oceans are still here because of cyanobacteria.

The deep oceans are a large component of the tidal coupling between Earth and Moon, transferring energy and angular momentum to the Moon and moving it farther out in its orbit. So in this strange and indirect way, microbes have indeed moved the Moon, and are the Earth's first astroengineers. Dr. Margulis was flabbergasted by this notion, having never thought of life this way.

But wait, there's more.

By transferring angular momentum and slowing the Earth's rotation, while moving the Moon further away, the distance from the center of the Earth relative to the gravitational center of the Earth-Moon system has shifted outwards; as the Moon continues to recede, the barycenter of the system is approaching the Earth's surface at half a millimeter per year, half a kilometer per megayear. About three billion years from now, the barycenter could be entirely above the surface, and the Earth could move back and forth by more than its diameter in relation to the barycenter (not quite, the ocean will boil away long before that, and the tectonic plates will cold and locked - greatly reduced tidal coupling).

In other words, the Earth is a moving target. As the position changes, some planet killing impactors will miss, others will hit. The wobble doesn't change the size of the impactor target, or the average impactor flux, but it does change which specific ones hit, and when. If the Earth was in a different position, the Chicxulub impactor might have missed, or another might have hit at a different time.

More interesting is the effect on the Earth's rotation. Assume an inevitable impact at Chicxulub latitude, 21 degrees north. However, in the billions of years between the emergence of cyanobacteria and the impact, the earth has turned about a trillion times, so a 1e-12 change in accumulated tidal effects over that vast timespan might change the longitude of the impact by 180 degrees. The very high sensitivity to rotation rate (and tidal losses, ocean depth, and the timing of the emergence of life) means that the impactor could have come down at any longitude. 21°N runs across a narrow strip of Mexico, more of Asia, all of Northern Africa, and a vast amount of ocean. An impact in mid-Pacific might have steam-cleaned the planet. A land impact in Northern Africa would have kicked up a lot of debris, but not caused major species extinction. As it was, the impactor landed in a sulfur deposit, creating vast amounts of hydrogen sulfide and sulfuric acid.

While the range of impact sites is not subject to Gaian feedback, this does illustrate how varied the results could have been, a random result of the emergence of life. This does not contradict Waltham's main thesis, indeed, it is one more contingent event involved in the "Lucky Planet" hypothesis. With an ever-so-slightly different cyanobacteria history, the continental surfaces might be sterile now, or still infested with dinosaurs.

But wait. there's more.

By the time of the Chicxulub impactor, the Earth was wobbling back and forth only 30 kilometers less than today. We may never know the exact time of the impact, except ... some of the ejecta from that impact ended up on the Moon. Someday, a massive collection program on the Moon can map the debris from that event, and many earlier impacts on Earth, Venus, and Mars, and the Moon itself. Where the debris landed on the Moon, and what overlies what, will yield details about trajectory, which will help us calculate the impact angle and perhaps even time of day and month. We may never know the exact year, but someday we may know the minutes from midnight!

This is somewhat disheartening to me, as I am interested in (someday) technologically processing the Moon's surface into quintillions of millimeter-scale robots, step one towards building self-sustaining lunar colonies. That will destroy the top layers of selenological evidence. OTOH, we will probably need such robots to collect all the data, and vast amounts of space-based computation to store and evaluate it. It will take centuries to produce the robots by exponential replication (micrometer-scale mechanisms are much slower than molecules), so I suppose we have plenty of time to decide how to do it. It would be fitting to process the micrometer-scale details of lunar particle data into nanometer-scale memory chips, as we strip down the top few centimeters of portions of the Moon.