An important realization reached by planetary scientists studying both solar and extrasolar planets is that Earth-like conditions represent a microscopic speck in a wide universe of possibilities for planets. As David Coppedge relates in a recent article at Evolution News on the inhospitable conditions prevailing on Saturn’s moon Titan:

The data have established that the physical properties of planets and moons (rotational axis, orbital eccentricity, length of day and year, atmosphere, elemental composition, type of star, radiation environment, etc.) vary to wide extremes. This implies that factors affecting habitability are contingent, not determined; they can take on arbitrary values over a wide range of possibilities.

We are so accustomed to Earth in all its fulness that we may fail to appreciate it for the paradise it really is compared to the nearly infinite divergent ways a planet could turn out. Following up on my previous article addressing some challenges inherent in terraforming Mars, and the sharp contrast it presents with Earth, let’s consider a couple of other key features needed for habitability that went awry there but converged to a comparative garden of life here.

Liquid Water

One of the key features regarded as essential for planetary habitability is liquid water. Although Martian rovers and reconnaissance orbiters have discovered H₂O in the Martian soil and frozen beneath its polar ice caps (coated with dry ice, or frozen CO₂), the relevance of this for the current habitability of Mars is minimal.

Despite the discovery of water, the implications for the search for life are not as great as they may seem at first glance. The topsoil is still, for all practical purposes, utterly dry due to the lack of free water.¹

However much water may have been on Mars in its distant past, today it is a desiccated planet….²

Analysis of the Martian surface shows substantial evidence of liquid water in the earlier history of the solar system.

Billions of years ago, Mars was much wetter and probably warmer than it is today….The evidence from the rovers has convinced many scientists that Mars once had large areas under liquid water.³

In recent times, however, the sub-zero average Martian surface temperature restricts any remaining water to a deep-freeze in polar ice caps and buried under the surface material. Three major habitability issues on Mars are all interdependent: Low atmospheric pressure, absence of free water, and frigid average temperatures. Furthermore, these critically non-ideal conditions are linked to core issues related to Mars’s low mass and non-existent planetary magnetic field. 

Turning off the magnetic field allowed the Sun’s wind of energetic particles and extreme ultraviolet light to strip away the atmosphere — and with it went vast amounts of water. The end product was today’s thin, cold atmosphere.

This wilderness of barrenness on Mars illustrates the complexity involved in obtaining true habitability, as we enjoy on Earth. 

A Lost Atmosphere

Conditions intrinsic to Mars caused its originally warmer and denser atmosphere to dissipate in ages past. When its denser atmosphere was lost, Mars also lost much of the associated atmospheric greenhouse effect, causing its surface temperature to plummet. Geological evidence indicates that Mars became a frozen desert almost 3 billion years ago.⁴ Current temperatures on Mars make our arctic regions seem balmy.

The median surface temperature on Mars is -85°F (-65°C). Because the atmosphere is so thin, heat from the Sun easily escapes Mars. Temperatures on the Red Planet range from the 70s°F (20s°C) to -225°F (-153°C).

Despite all the attributes of Mars that make it barren today, couldn’t we at least temporarily transform that environment by importing both air and water and then planting the crops we need? Dreaming about growing anything on Mars leads us to yet another significant deficit in the habitability of the fourth planet from the Sun. What we call dirt on Earth, or soil, is a rich, curated, gourmet composite of inorganic and organic material possessing essential nutrients and water-retention properties. In terms of its comparative value for sustaining life, Earth’s surface is living gold and Mars’s is dead lead.

Mars is covered in a blanket of loose, dust-like material called regolith. Think of it as Martian sand. The regolith contains few nutrients, not enough for healthy plant growth, and it hosts some nasty chemicals called perchlorates, used on Earth in fireworks and explosives.

The topsoil is still, for all practical purposes, utterly dry due to the lack of free water. Worse, scientists believe that organics can’t survive in the surface soil [on Mars]….⁵

The continents on early Earth were likewise once devoid of life-supporting properties. 

The continents began as chunks of silicate (granites, shales, and sands). However, for vascular or flowering plants to produce the food resources animals need, the granites, shales, and sands needed further transformation into prodigious quantities of soil, or dirt. Only soil possesses the water and mineral concentration and retention that vascular plants require.⁶

The Origin of Soil

On Earth, the formation of fertile soil arose gradually through the action of a variety of living organisms.

Earth’s dirt is one of the things that sets it apart from the other rocky lifeless planets out there. But geologically speaking soil hasn’t really been around that long.

Earth is 4.54 billion years old, and yet the rich reddy-brown sediments that we think of as soil didn’t appear until 450 million years ago. We used to think that soil was created by rivers weathering bare rock, but research…suggests that it is land plants we need to thank for our soil.

Before land plants appeared on continents, Earth’s surface material underwent preparatory transformation through simpler biological organisms.

A complex symbiotic ecosystem known as biological soil crust (BSC), or cryptogamic crust, turned Earth’s barren landmasses into nutrient-rich surfaces that made possible the existence and flourishing of advanced plants. BSC is a blend of cyanobacteria, diatoms, fungi, algae, mosses, liverworts, lichens, sand, and clay.⁷

It Takes Life to Support Life

Apparently, simple living organisms must exist for eons on a planet before more advanced life can thrive. The BSC organisms engaged in photosynthesis, structural reorganization of the sand, clay, and shale particles, transformation of atmospheric nitrogen to nitrates and ammonium minerals (serving as fertilizers), and soil pH regulation. On Earth, the action of BSC organisms that resulted in extensive soil coverage didn’t happen overnight, but throughout a geological age spanning 1,400 million years.⁸ The enormity of this time span helps us to appreciate the commensurate effort that would be required to “terraform” a planet to allow plants to grow for the flourishing of advanced life.

So what is the prognosis for terraforming Mars? See an artist’s imaginative depiction of what that would like at the top of this article. According to Dr. Sven Bilén at Penn State:

Providing oxygen, water and food in the right proportions is extraordinarily complex. On Earth, scientists have tried to simulate this in Biosphere 2, a closed-off ecosystem featuring ocean, tropical and desert habitats. Although all of Biosphere 2’s environments are controlled, even there scientists struggle to get the balance right. Mother Nature really knows what she is doing.

Professor Bilén is realistic in his cautionary appraisal about making Mars a habitable alternative Earth. 

In fact, all of the technologies I’ve described are far beyond current capabilities at the scale needed to terraform Mars. Developing them would take enormous amounts of research and money, probably much more than possible in the near term.

“I No Longer Have Doubts”

Multiple bio-congenial design elements have earned Earth the title of The Privileged Planet. Or, as geophysicist David Waltham chooses to describe seemingly intentional design, Earth is “a very peculiar place”:

I no longer have doubts. The evidence points toward Earth being a very peculiar place: perhaps the only highly habitable planet we will ever find.⁹

To prepare a planet to support millions of diverse species, including advanced life, speaks of a teleological, goal-directed, inter-connected sequence of actions. Many of these steps require the development of complex, information-rich life forms whose metabolic activities allow them to participate in the sophisticated processes required for transforming a barren planet into a thriving ecosystem. 

If “Mother Nature” is merely a figure of speech denoting the undirected consequences of cosmic and geological forces, then it is woefully inadequate as a credible explanation for producing the habitability we find on Earth. On the other hand, if Mother Nature is more of a politically acceptable substitute for the design activities of a creator possessing foresight and purpose, then we have an appropriate match between the proposed cause and the observed effect.

Notes

1. David Szondy, September 27, 2013, https://newatlas.com/curiosity-water/29194/?itm_source=newatlas&itm_medium=article-body
2. https://newatlas.com/great-places-to-live-mars/45654/
3. Thomas T. Arny and Stephen E. Schneider, Explorations: An Introduction to Astronomy, 8th ed. (New York: McGraw-Hill, 2017), p. 238.
4. Arny and Schneider, Explorations (2017), p. 242.
5. David Szondy, September 27, 2013, https://newatlas.com/curiosity-water/29194/?itm_source=newatlas&itm_medium=article-body.
6. Hugh Ross, Improbable Planet: How Earth Became Humanity’s Home (Grand Rapids: Baker Books, 2016), p. 139.
7. Hugh Ross, Improbable Planet, p. 139.
8. Hugh Ross, Improbable Planet, p. 140.
9. David Waltham, Lucky Planet: Why Earth is Exceptional — and What that Means for Life in the Universe (New York: Basic Books, 2014), p. 2.