From Chapter 5. “Parents: Sol, Luna, and Gaia as a Triple Relationship”

Within our Soular System, Sol and Luna are essentially the parents of Gaia, without whose tripartite relationship the emergence and abundance of her future organic children would have been severely constrained.

Sol is four hundred times larger than Luna and is four hundred times farther away. This exact and unique correspondence not only enables total solar eclipses to occur, also but numerous other valuable influences and processes to ensue.

With Luna’s orbit around Gaia, though, being around 5 degrees from the plane of Gaia’s orbit around Sol, solar eclipses only happen between two and five times each year and total solar eclipses only roughly every eighteen months: at a New Moon and specifically when Luna’s orbit intersects the solar plane. Given that at the time of a New Moon, Luna lies between Gaia and Sol, not only do they present an awe-inspiring cosmic sight, but the combined gravitational influence of her parents, along their arc of totality around Gaia, raises the highest of her tides.

However, in the earliest epoch of Gaia’s Soular family, before and during her early years as a planet, Sol was much fainter than now. So, when she was birthed around 4.54 billion years ago and located at the same distance as now from Sol, unlike later epochs, where his radiant heat enabled the presence of liquid water, some other influence needed to supply sufficient heat for that to be possible during her early years.

The most significant of these was the presence of Luna. The Gaia-Luna relationship is extraordinary and more of a binary system than a planet and satellite. Luna, recognized by many traditional societies as Gaia’s “mother,” is the largest moon in relation to its planet in the entire Soular System with the exception of Pluto and his moon Charon.

Even more astounding is the most likely way in which Luna and Gaia in her final form came into being.

Lunar rock samples collected by the Apollo astronauts show a great similarity with the rocks of Gaia’s crust, suggesting they had a common origin. Named after Theia, in Greek myth the mother of the moon goddess Selene, the Theia hypothesis posits that a body, about the size of Mars, slammed into the protoplanetary Gaia. Causing an immense ejection of material that formed Luna, the core of Theia plunged deep into Gaia where she has remained ever since.1 Indeed, some of her remains may be present in the form of two huge masses of ancient rock: one buried under Africa and the other beneath the Pacific Ocean.2 Known as large low-shear-velocity-provinces, or LLSVPs, denser and with a different chemical composition to Gaia’s geosphere, they have sunk to the base of her mantle rocks, straddling her core and possibly have provided a further rotational stabilizing influence.

In addition to the rocks of Gaia and Luna being very similar, Theia’s remains should thus also be found in the lunar rock samples. And, indeed, rocks collected from the deepest locations on Luna’s surface reveal relatively less similarity with Gaian rocks and are more attributable to being relics of Theia.3

Furthermore, there’s growing evidence that the birth of the Gaia-Luna system was even more extraordinary. It suggests that Theia may have originated not in an orbit close to Gaia’s but some further distance toward the outer Soular System. Unlike the arid environment of the inner Soular System, its outer echelons were replete with water and carbon-based materials. In this scenario, Theia would likely have brought with her these vital ingredients for the emergence of organic life and perhaps delivering much of the water that would make Gaia the bluegreen planet she became.4

It also seems that Theia delivered two further, interrelated and inestimable benefits. For unlike Venus—Gaia’s close sibling in planetary scale—thanks to Theia, Gaia gained a much larger and denser iron-nickel metallic core and a correspondingly much shallower crust; both, as we’ll see, are essential for the emergence and evolution of her future organic children. Indeed, the scale of her metallic core causes Gaia to be the densest planet in the Soular System.

The primordial heat of her core, convected through the magma of the molten mantle above and through to her volatile crust, evaporated the gases of her first atmosphere and, likely, huge amounts of hydrogen (and its heavier variant, deuterium, where a neutron joins the proton of its nucleus) and oxygen to form the two “flavors” of water: light (H2O) and heavy (D2O).

While the search for the possibly multiple sources of Gaia’s abundance of water continues to be studied, mineralogical analysis shows that her primordial ocean was present by around 4.4 billion years ago.5 (Commonly, “billion years ago” is abbreviated as Ga, for example 4.4 Ga, which we’ll use going forward.)

Using the ratio (D/H) of the two flavors of her water is a key test for compatibility and so origin, and it seems increasingly likely that the major contributors were Gaia herself as a proto-planet,6 Theia, and then a later bombardment of water-bearing asteroid impacts emanating from the asteroid belt, likely triggered by Jupiter’s grand tack and lasting hundreds of millions of years until around 3.8 Ga.

Heavy with carbon dioxide, her powerful atmospheric pressure at this earliest era was vital, as Gaia cooled, to prevent her liquid water evaporating into space. The size of her core and its continuing high temperature have also remained crucial for her strong magnetic field ever since, protecting her from harmful UV radiation and charged particles emitted by Sol that otherwise could have stripped her entire atmosphere away.

In addition, the heat of her inner core (solid and crystalline due to the immense pressure) caused the lighter rocks of the overlaying mantle to remain molten. This enabled the surface rocks of her shallow crust not only to float but, driven by circulating convection currents in the underlying mantle, to facilitate the cracking of her crust into a number of tectonic plates and the subsequent recycling processes of their rocks. As we’ll go on to explore, the timing—starting between half a billion and one billion years after Gaia’s birth—and the scale of such processes progressively recycles and modifies her geosphere, hydrosphere, and atmosphere, enabling (over billions of years) a great variety of environmental opportunities and evolutionary niches for her emergent biosphere.

Theia’s greatest gift, though, was perhaps Luna herself, whose relative size, proximity, and orbital resonance has enabled Gaia’s long and continuing evolutionary journey for some 4.5 billion years.

Gaia’s distance, just under a 150 million kilometers (93 million miles) from Sol, locates her in a goldilocks zone, neither too hot nor too cold for liquid water to exist on her surface. Yet during her early years, with Sol much fainter than now, instead of Gaia’s water being frozen into a global snowball for at least her first billion years of existence, geological evidence and the rapid emergence of organic life-forms shows this wasn’t the case.

Instead, two other compensating circumstances crucially prevailed. Soon after Luna was formed from the impact of Gaia with Theia, she was only around 20,0 kilometers (12,4 miles) away, compared to an average of some 384,0 kilometers (238,6 miles) now. Gaia at that time was also spinning on her axis far more rapidly, with a day then perhaps as short as five hours or even less.

These two key factors meant that the gravitational interaction between Gaia and Luna was much more powerful than now, with the push-pull of Luna’s tidal influences warming Gaia and also likely triggering massive volcanic eruptions, bringing huge amounts of deep mantle magma to her surface and causing crustal off-gassing. Generating a still thicker carbon dioxide rich atmosphere trapping yet more heat and also squeezing water to the surface, her primordial oceans rapidly formed, themselves helping to cool the magma into solid rock.7

Had their relationship, though, remained as it was, while enabling her to avoid a frozen fate, the powerful tides raised by Luna and the turmoil of associated and continuing volcanism would have destabilized Gaia’s surface. Preventing water oceans from forming or whipping them into unimaginable maelstroms, Luna would have instead forestalled the conditions necessary for the emergence of Gaia’s organic children.

However, within at most twenty million years, due to the frictional tidal drag of their interactions, Luna began to move further away, and Gaia’s rotation began to slow down to her current twenty-four hours, conserving the angular momentum of their combined system. Gradually the two also became tidally locked, so that Luna’s rotation around her axis correlated with her orbital rotation and so presenting only her near face to Gaia.

Such tidal, or synchronous, 1:1 resonance, maximizes the stability of their binary system while also offering an ability to clear of debris a combined orbit around Sol, and so enabling their benevolent relationship to continue for the billions of years since.

Although continuing to gradually move apart, its effect beginning around 4.25 Ga and peaking around 4.0 Ga when Luna was around 113,0 kilometers (70,0 miles) distant from Gaia, she gave yet another gift of inestimable value to her daughter.

At that time, the young Sol, while fainter than today, was expelling a much stronger solar wind. Establishing his protective sheath of the heliosphere for the entire Soular System also cleared its inner region, where Gaia is located, of much of the remaining material left over from the formation of the terrestrial planets.

Gaia was then beginning to terraform into a habitable planet, and her early atmosphere was vital to provide the heat and pressure for the formation of her surface oceans and the potential emergence of her earliest organic life-forms. With the dynamo of her own magnetic field ramping up, perhaps, though, less strong than today, the protective magnetosphere it provided would have been insufficient to prevent the intense solar wind from stripping the volatile gases of her atmosphere away.

Between 4.2 and 2.7 Ga, Luna, too, had a primordial magnetic field, its dynamo driven by the gravitational tug from Gaia causing Luna’s small liquid core and its mantle to rotate at different rates. However, as they continued to move away from each other, the stirring of Luna’s dynamo eventually reduced to zero.

In Gaia’s early years, however, its strength at Luna’s surface, as powerful as Gaia’s is at her surface today, coupled with their proximity, was critical. It enabled them to couple their magnetospheres together, forming a sufficiently protective bulwark against the intense solar wind and thereby ensuring the survival of Gaia’s vital atmosphere.8

Continuing to ensure Gaia’s thriving, and overlighting the emergence and development of her organic children as the two continued to move apart, Luna’s moderated tidal influences have helped to dissipate heat and disperse nutrients in Gaia’s waters—optimizing energy flows, nurturing the abundance of food chains, and so augmenting the scale and speed of evolutionary speciation and diversity.
Now, they’re settled into a distance between mother and daughter averaging just over 384,0 kilometers (238,6 miles), and only increasing by a miniscule 4 centimeters (1.5 inches) per year. Luna will continue to benefit Gaia and her daughter’s own children for the rest of their lives; perhaps five billion more years, before Sol depletes his hydrogen fuel, probably expanding to the orbit of Mars and becoming a red giant star.