The Cosmic Zoo: The (Near) Inevitability of the Evolution of Complex, Macroscopic Life

Bains, William; Schulze‐Makuch, Dirk

doi:10.3390/life6030025

Cited by 33 publications

(42 citation statements)

References 188 publications

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“…For our universe, this should be on the gigayear timescale, an estimate suggested in [68]. This subscribes to the notion that this amount of time is both necessary and sufficient for a biosphere to achieve the complexity we observe, as advocated for example in such papers as [69]. Alternative viewpoints are certainly taken on this matter, which makes the adoption of this criterion that of a personal preference at the moment.…”

Section: Is Photosynthesis Possible Around Red Dwarfs?mentioning

confidence: 94%

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Sandora

2019

Universe

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In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario.

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Section: Is Photosynthesis Possible Around Red Dwarfs?mentioning

confidence: 94%

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Sandora

2019

Universe

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“…While complex multicellularity has evolved at least six times (Knoll, ), animals represent the only living instance of complex multicellularity evolving from wall‐less microbial eukaryotes capable of phagocytosis (Mills & Canfield, ; Mills, Francis, & Canfield, ). It is possible that some evolutionary events destroy the conditions needed for them to evolve in other lineages (reviewed in Bains & Schulze‐Makuch, ). However, brown algae evolved complex multicellularity in a world already populated with multicellular red algae and embryophytes, including seagrasses (Mills, Francis, & Canfield, ), and fungi have evolved complex multicellularity numerous times (Nagy, Kovács, & Krizsán, ).…”

Section: Point–counterpoint Argumentsmentioning

confidence: 99%

On the co‐evolution of surface oxygen levels and animals

et al. 2020

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Few topics in geobiology have been as extensively debated as the role of Earth's oxygenation in controlling when and why animals emerged and diversified. All currently described animals require oxygen for at least a portion of their life cycle. Therefore, the transition to an oxygenated planet was a prerequisite for the emergence of animals. Yet, our understanding of Earth's oxygenation and the environmental requirements of animal habitability and ecological success is currently limited; estimates for the timing of the appearance of environments sufficiently oxygenated to support ecologically stable populations of animals span a wide range, from billions of years to only a few million years before animals appear in the fossil record. In this light, the extent to which oxygen played an important role in controlling when animals appeared remains a topic of debate. When animals originated and when they diversified are separate questions, meaning either one or both of these phenomena could have been decoupled from oxygenation. Here, we present views from across this interpretive spectrum—in a point–counterpoint format—regarding crucial aspects of the potential links between animals and surface oxygen levels. We highlight areas where the standard discourse on this topic requires a change of course and note that several traditional arguments in this “life versus environment” debate are poorly founded. We also identify a clear need for basic research across a range of fields to disentangle the relationships between oxygen availability and emergence and diversification of animal life.

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“…Instead of a rise of oxygen, perhaps genetic diversification during the Vendian allowed for the gradual development of complex animal forms that triggered the Cambrian Explosion [105]. Such scenarios would indicate that oxygen, at best, may only be a facilitating condition, but not the defining one for the evolution of animal life [105].…”

Section: The Importance Of Oxygen-poor Planets In the Search For Extrmentioning

confidence: 99%

A More Comprehensive Habitable Zone for Finding Life on Other Planets

Ramirez

2018

Geosciences

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The habitable zone (HZ) is the circular region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. Space missions employ the HZ to select promising targets for follow-up habitability assessment. The classical HZ definition assumes that the most important greenhouse gases for habitable planets orbiting main-sequence stars are CO2 and H2O.Although the classical HZ is an effective navigational tool, recent HZ formulations demonstrate that it cannot thoroughly capture the diversity of habitable exoplanets. Here, I review the planetary and stellar processes considered in both classical and newer HZ formulations. Supplementing the classical HZ with additional considerations from these newer formulations improves our capability to filter out worlds that are unlikely to host life. Such improved HZ tools will be necessary for current and upcoming missions aiming to detect and characterize potentially habitable exoplanets.

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The Cosmic Zoo: The (Near) Inevitability of the Evolution of Complex, Macroscopic Life

Cited by 33 publications

References 188 publications

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Multiverse Predictions for Habitability: The Number of Stars and Their Properties

On the co‐evolution of surface oxygen levels and animals

A More Comprehensive Habitable Zone for Finding Life on Other Planets

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