In this step, we will determine whether the world has native life, the nature of that life, and how complex it has become at the present time.

The evolution of complex life forms takes time, and also requires that local conditions be congenial. We will estimate the amount of time it requires for seven specific evolutionary steps to take place, affected by the world’s other properties. In the process, we will sketch out the world’s evolutionary history.

Procedure

Begin by noting the current age of the star system, as established in Step Four. For any of the seven following events, if the total time to the event is greater than the star system’s age, then that event has not yet taken place on the world under development. Any further events that depend upon that one can be ignored.

Abiogenesis (Deep Hydrothermal Vents)

If all of the following conditions are true for the world under development:

• Class II, Class III, Class IV, or Class V atmosphere
• Moderate, Extensive, or Massive prevalence of water
• Molten, Soft, Early Plate, Mature Plate, or Ancient Plate lithosphere
• World does not have Fixed Plate Tectonics

Then roll 3d6, multiply by 30 million years, and make a note of the result as the time to deep abiogenesis.

If the age of the star system is greater than this, then the world has native life which derives energy and nutrients from volcanic vents at the bottom of its oceans.

Note that the world does not require exposed liquid-water oceans in order for this form of life to appear. For example, there is speculation that life may exist on Jupiter’s moon Europa, in a large liquid-water ocean beneath the icy surface.

Abiogenesis (Surface Refugia)

If all of the following conditions are true for the world under development:

• Class III or Class IV atmosphere
• Moderate or Extensive prevalence of water
• Average surface temperature is at least 265 K
• Lithosphere is Molten, Soft, Early Plate, Mature Plate, or Ancient Plate
• World does not have Fixed Plate Tectonics

Then roll 3d6, multiply by 100 million years, and make a note of the result. Also, if the world has undergone deep abiogenesis (see above), roll 3d6, multiply by 75 million years, add the time to deep abiogenesis, and make a note of that final result as well. Take the lesser of these two times and make note of it as the time to life in surface refugia.

If the age of the star system is greater than this, then the world has native life which derives energy and nutrients from sources in shallow water or on exposed land. Very early on, this life will require special conditions that sometimes occur in shallow oceans, on beaches, or in fresh-water ponds. These refugia form the basis for all later expansion of life across a world’s surface.

Special Case: Lifeless Worlds

Note that all of the following evolutionary events are dependent on the presence of life in either the deep oceans or in surface refugia. If a world doesn’t meet the criteria for either of the above events, then it will be barren and effectively lifeless. It’s possible that some hardy form of bacterial life clings to existence, but it will be difficult to detect and will have no significant effect on the world’s environment.

Multicellular Life

If the world has undergone deep abiogenesis (see above), then roll 3d6, multiply by 75 million years, and then add the time to deep abiogenesis. Make a note of the final result as the time to multicellular life.

If the age of the star system is greater than this, then the world’s native life has developed the ability to form multicellular organisms. These organisms will likely be simple and primitive for a very long time, but they will form the basis for all future complex ecosystems based on plant and animal life.

Photosynthesis

Photosynthesis is critical to the development of a complex surface ecology for a world, such as exists on Earth. Early forms of photosynthesis are likely to appear very soon after the development of surface refugia. However, the form of photosynthesis with which we are most familiar – the so-called oxygenic photosynthesis that releases free oxygen as a by-product – takes much longer to evolve.

In any case, the difficulty of developing photosynthesis is strongly dependent on the color of light that a world receives from its primary star.

Stars similar to Sol produce most of their radiation in the visible-light range, which passes easily through the transparent atmosphere of an Earth-like world. Smaller and cooler stars (K-class and especially M-class) produce more of their radiation in the infrared bands, which have more trouble penetrating an atmosphere. Furthermore, the chemical pathways involved in photosynthesis are most effective at certain visible light wavelengths. A world with a small, cool primary star receives less such light, and may take much longer to develop photosynthetic life.

If the world has life in surface refugia (see above), and its primary star is not a brown dwarf, then refer to the following table:

Photosynthesis Table
Primary Star Class	Photosynthesis Development Timescale
A, F, or G0-G7	100 million years
G8-G9	105 million years
K0	110 million years
K1	115 million years
K2	120 million years
K3	130 million years
K4	145 million years
K5	160 million years
K6	180 million years
K7	210 million years
K8	240 million years
K9	270 million years
M0	300 million years
M1	360 million years
M2	480 million years
M3	600 million years
M4	800 million years
M5-M9	1 billion years

Roll 3d6, multiply by the Photosynthesis Development Timescale entry for the spectral class of the world’s primary star, and then add the time to life in surface refugia. Make a note of the final result as the time to photosynthesis.

If the age of the star system is greater than this, then the world’s native life has developed the ability to synthesize food by using sunlight to drive the necessary chemical reactions. Organisms which develop this trait will establish all of the world’s families of plant life.

Oxygen Catastrophe

Although the development of oxygenic photosynthesis opens many new opportunities for a world’s ecology, it can also be immensely harmful for existing life. Life forms which arose in the absence of oxygen will often find it to be actively poisonous. The period of Earth’s history during which free oxygen became prevalent is sometimes called the Oxygen Catastrophe.

After oxygenic photosynthesis develops, oxygen will be released by photosynthetic organisms, but at first that oxygen will tend to be dissolved in the oceans, or it will combine with exposed materials on land. It may take a long time for photosynthesis to build up significant free oxygen in a world’s atmosphere.

If a world has developed photosynthesis (see above), roll 3d6, multiply by 1.5 and by the appropriate entry in the Photosynthesis Table, and then add the time to photosynthesis. Make a note of the final result as the time to the Oxygen Catastrophe.

If the age of the star system is greater than this, then the world’s oceans, land surfaces, and atmosphere have all become saturated with free oxygen and oxygen compounds. Many earlier forms of anaerobic life will likely have been driven into extinction, but new aerobic forms will have arisen which can tolerate or even take advantage of the available oxygen.

Animal Life

Although multicellular life may appear quite early in a world’s history, the development of animals – complex multicellular organisms that are mobile and survive by eating organic matter – may take a very long time. The appearance of free oxygen in the environment can promote the development of animals, but it is theoretically possible for anaerobic animals to evolve as well.

If a world has developed multicellular life (see above), roll 3d6, multiply by 300 million years, and then add the time to multicellular life. If the result is longer than the time to the Oxygen Catastrophe, then subtract half of the difference. Make a note of the final result as the time to animal life.

If the age of the star system is greater than this, then the world will have given rise to complex animal life. Equivalents on Earth would be life forms that first appeared late in the Precambrian period, leading up through the so-called Cambrian Explosion about 540 million years ago. These ancestral forms eventually gave rise to all of the animal phyla that exist today.

Pre-Sentient Life

The earliest animals are driven purely by biological programming, the tropisms and instincts that they evolve to govern their behavior. Eventually, however, animal life will develop more elaborate systems for gathering and processing sensory data. Some animal species will even develop the first potential for self-aware, tool- and language-using minds. We will use the term pre-sentient for such species.

If a world has developed animal life (see above), roll 3d6. Multiply the result by 50 million years if the world has hydrographic coverage of less than 100% (from Step Twenty-Four), or by 100 million years otherwise. Add the time to animal life to compute the final result. Make a note of the final result as the time to pre-sentient life.

If the age of the star system is greater than this, then the world will have given rise to one or more classes of animal life that have advanced nervous systems and may be capable of complex learned behavior. Equivalents on Earth would be the behaviorally complex animals that first appeared late in the Triassic period, about 300 million years ago.

Examples

The Arcadia star system is 5.6 billion years old, so Alice makes a note of this as the endpoint for her generation of the evolutionary history of both Arcadia IV and Arcadia V.

Arcadia IV

Arcadia IV has a Class III atmosphere, Extensive water, and a Mature Plate Lithosphere with Mobile Plate Tectonics. It meets the criteria for deep abiogenesis. Alice rolls 3d6 for a result of 12, multiplying that by 30 million years, and she makes a note that the time to deep abiogenesis is 360 million years.

Arcadia IV also has an average surface temperature of 286 K, so the planet has liquid-water oceans and meets the criteria for surface refugia. Alice rolls 3d6 for a result of 10, multiplying that by 100 million years, and she makes a note that the first result is a full 1 billion years. She also rolls 3d6 for a result of 8, multiplying that by 75 million years and adding the time to deep abiogenesis of 360 million years, for a second result of 960 million years. The time to life in surface refugia is the lesser of the two results, or 960 million years. Apparently, Arcadia IV’s later surface life derives from forms that first evolved near the deep hydrothermal vents.

Meanwhile, Alice rolls 3d6 for a result of 10, multiplying that by 75 million years and adding the time to deep abiogenesis of 360 million years. She makes a note that the time to multicellular life is also about 960 million years. Even while some of the deep-vent life forms were colonizing the planet’s surface, other organisms were beginning to experiment with multicellularism.

Arcadia IV has life in surface refugia, so it is likely to develop photosynthesis. The primary star of the system has spectral class of K2. Alice rolls 3d6 for a result of 14, multiplies that by 120 million years, and adds the time to life in surface refugia of 960 million years. She makes a note that the time to photosynthesis is about 2.64 billion years.

From there, Alice moves on to estimate the time to the Oxygen Catastrophe. She rolls 3d6 for a result of 14, multiplies that by 1.5 and then by 120 million years, and adds the time to photosynthesis. She makes a note that the time to the Oxygen Catastrophe is 5.16 billion years. The development of an oxygen atmosphere on Arcadia IV apparently took noticeably longer than it did on Earth!

To estimate the time of appearance of animal life, Alice rolls 3d6 for a result of 14, multiplies that by 300 million years, and adds the time to multicellular life of 960 million years. Her first estimate for the time to animal life is (by an odd coincidence) 5.16 billion years, or almost exactly the same time as the Oxygen Catastrophe. She makes a note of that as well.

Arcadia IV has hydrographic coverage of about 70%. Alice rolls 3d6 for a result of 9, multiplies that by 50 million years, and adds the time to animal life of 5.16 billion years. She makes note of the result: 5.61 billion years, or slightly more than the total age of the star system. Alice decides that Arcadia IV does have complex ecosystems of plants and animals, but that the first pre-sentient species are just now beginning to appear. The planet has lots of equivalents to fish, insects, amphibians, and small reptiles, but is only starting to develop the equivalent of dinosaurs or primitive mammals.

Arcadia V

Arcadia V has a Class III atmosphere, Moderate water, and a Mature Plate Lithosphere with Fixed Plate Tectonics. Since it has Fixed Plate Tectonics, it does not meet the criteria for deep abiogenesis.

Arcadia V has an average surface temperature of 221 K, which does not meet the criteria for abiogenesis in surface refugia.

Since all of the evolutionary events that follow are dependent on abiogenesis taking place in at least one of these two locations, Alice quickly concludes that Arcadia V is effectively lifeless. There may be some form of hardy bacterial life, lurking in water deposits under the surface, but this isn’t sufficient to have any significant effect on the planet’s environment.