Physics, Earth & Space Icon Physics, Earth & Space

When Evolving Life, Don’t Forget the Astrophysics

Astrophysics

Much of evolutionary theorizing takes place wearing a sun visor. The eyes of Darwinian biologists look down at what’s happening on the ground or in the water, avoiding the blinding sunlight overhead. But that sunlight, traversing 93 million miles of space, sheds light on realities that must not be ignored when trying to understand how life appeared and changed on the earth. 

Evolution is hard enough just waiting for the right lucky mutations to occur (Douglas Axe can tell you all about that). While hoping for mutational luck to add up and actually do something (hear Andrew Jones on that), the Darwinist must get the astrophysics right, too. Evolution will never get off the ground on an inhospitable planet. Some factors for habitability are (as mathematicians like to say) “non-trivial.”

Wild Swings

Many people have heard of “habitable zones” where liquid water can exist. Peter Kelley, however, reminds us that being in the zone is not enough — even if you orbit a lucky star. In news from the University of Washington, he announces, “Orbital variations can trigger ‘snowball’ states in habitable zones around sunlike stars.” 

Aspects of an otherwise Earthlike planet’s tilt and orbital dynamics can severely affect its potential habitability — even triggering abrupt “snowball states” where oceans freeze and surface life is impossible, according to new research from astronomers at the University of Washington. [Emphasis added.]

The UW astronomers studied just two factors — obliquity and eccentricity. Separately and together, they can cause make-or-break situations on a nice planet trying to evolve life around a gentle star. Too much obliquity, or tilt, causes seasonal changes that can lead to advancing ice sheets, blanketing the planet with snow, even within the habitable zone. This was a surprising finding to those who thought high obliquity would actually warm the planet. 

The other factor, eccentricity, could have the same effect, swinging the planet in and out of the zone. Russell Dietrick, lead author of a forthcoming paper about this, cautioned that “We shouldn’t neglect orbital dynamics in habitability studies.” Fortunately, the earth scores well on both obliquity (23.5 degrees tilt) and eccentricity (0.0167, nearly circular).

Death Rays

Ah, space. So serene, so quiet, so timeless. Not! It’s a battle scene out there. Solar rays and cosmic rays can accelerate electrons to nearly the speed of light. If those killer rays hit DNA too often, you’re not going to get evolution; you’re going to get extinction. Fortunately, the earth has three protective measures against the barrage: the ozone layer, which filters UV light; a strong magnetic field, which traps charged particles; and the Van Allen Belts, which shield the surface from the most energetic electrons and ions.

The Van Allen Belts, discovered sxity years ago by America’s first satellites, are quite amazing. Since 2012, two Van Allen Probes have been studying the belts and how they interact with electrons from the solar wind. Some of the electrons become accelerated to near light speed in the outer Van Allen Belt. A few years ago, Baker et al. thought they had inferred a very thin, impenetrable “space shield” through which “killer electrons” could not pass. This was located in a “slot” between the inner and outer lobes. Now, Ozeke et al., writing in Nature Communications, finesse those findings somewhat without changing the conclusions about habitability. They claim there is not an impenetrable layer, but rather a more gradual decline of the energy of the electrons as they traverse the slot between the lobes. The bottom line, though, is that few of the high-energy particles reach the surface of the earth; most are stopped before they can reach the inner lobe. Do we see a Goldilocks situation here?

Here we presented evidence showing that ULF [ultra low frequency] wave radial diffusion can transport the ultra-relativistic electron inward down to L ~ 2.8 [earth radii] consistent with the observed electron flux. Specifically, we show that the rates of ULF wave transport are both: (i) fast enough to rapidly transport electrons inward to the barrier during the period of the duration of a typical magnetic storm; (ii) slow enough once the storm abates to subsequently maintain the observed very steep flux gradient at the inner edge of the apparent barrier and hence effectively prevent any subsequent penetration further Earthward into the slot.

Would other planets need something like Van Allen Belts to enable life? 

Such an apparent barrier to ultra-relativistic radiation flux might also be expected in other astrophysical plasma systems perturbed aperiodically by a bursty stellar wind. If such systems have different characteristics, such an apparent barrier could however be located at a different radial distance from the magnetised body than in the terrestrial case.

To keep the barrier at a safe radial distance, it would appear necessary to finely tune the outflow of the stellar wind, the strength of the magnetic field, the height of the lobes, and their resilience against large bursts from the star. Don’t forget the obliquity and eccentricity, too.

Astrophysical Nudging

Evolutionists sometimes relish destructive events, seeing them as blessings in disguise. Examples include the notion that ultraviolet radiation could have created the building blocks of life, or the idea that asteroid impacts could have delivered prebiotic molecules to the earth. Why not let death rays penetrate the atmosphere? Aren’t those agents of mutation, the celebrated source of genetic variations that Darwin can select? 

There’s a kinder, gentler astrophysical phenomenon that some Darwinians look to for a kind of celestial massage, nudging life to ebb and flow with its soothing fingers. It’s the notion of Milankovitch Cycles. These are long-term variations in celestial mechanics that might affect climate on the earth, giving opportunities for heat-loving and cold-loving organisms to flourish in their own epochs. The idea is controversial. Nobody knows exactly how much the climate could be affected by these very slight cyclic variations which interact and overlap in complex ways. 

A new paper in PNAS by Crampton et al. claims a correlation (but not causation) between “macroevolutionary rates” in certain marine organisms called graptoloids and “Milankovitch grand cycles.” Careful reading, though, reveals a lot of guessing and hoping.

There has been long-standing debate about the relative roles of intrinsic biotic interactions vs. extrinsic environmental factors as drivers of biodiversity change. Here, we show that, relatively early in the history of complex life, Milankovitch “grand cycles” associated with astronomical rhythms explain between 9 and 16% of variation in species turnover probability (extinction probability plus speciation probability) in a major Early Paleozoic zooplankton group, the graptoloids. These grand cycles would have modulated climate variability, alternating times of relative stability in the environment with times of maximum volatility, which influenced oceanic circulation and structure and thus, phytoplankton populations at the base of the marine food web.

In looking at their Materials and Methods, though, we see only a very restricted time range and a restricted set of organisms. Graptoloids are filter-feeding hemichordates with some diversity, but no real “macroevolution” in terms of new body plans, organs or taxons. We also see that only 9 to 16 percent of variation fits the Milankovitch cycles; what about the other 91 percent to 84 percent that don’t fit? There is so much wiggle room in this theory, it could explain anything. “We cannot say with certainty whether the observed cyclicity in graptoloid species turnover is driven more by speciation or extinction,” they say. The idea that climate change is a “driver” of macroevolution seems silly. It’s like attributing the Cambrian explosion to a rise in oxygen.

Conclusions

Set aside this last idea as weak at best, since they admit in the end, “This may suggest that extinction in the graptoloids was influenced more strongly by these astronomical cycles than speciation, although further testing is required.” 

The observable, testable evidence presented earlier shows that astrophysical factors present more evidence of fine-tuning for habitability. When we observe tuning, we usually infer the actions of a tuner. A tuner had a goal in mind and brought the necessary factors together to achieve it. For life on earth, those factors included biological, geophysical, and astrophysical requirements. Unless you really want to believe in incredible luck, the combination of multiple, disparate, independent factors coming together to permit life speaks powerfully of design.

Image: “Snowball Earth,” via NASA.