The Medea hypothesis is a term coined by

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...

Peter Ward for a hypothesis that contests the Gaian hypothesis and proposes that

multicellular life A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- ...

, understood as a

superorganism A superorganism or supraorganism is a group of synergetically interacting organisms of the same species. A community of synergetically interacting organisms of different species is called a holobiont. Concept The term superorganism is used mo ...

, may be self-destructive or suicidal. The metaphor refers to the mythological

Medea In Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the ...

(representing the Earth), who kills her own children (multicellular life). In this view, microbial-triggered

mass extinctions An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It ...

result in returns to the microbial-dominated state it has been for most of its history.

Examples

Possible examples of extinction events induced entirely or partially by biotic activities include: * The

Great Oxidation Event The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Paleoproterozoic era when the Earth's atmospher ...

, 2.45 billion years ago, believed to be responsible for the mass poisoning of anaerobic microbes to which oxygen was toxic, and for the

Huronian glaciation The Huronian glaciation (or Makganyene glaciation) was a period where several ice ages occurred during the deposition of the Huronian Supergroup, rather than a single continuous event as it is commonly misrepresented to be. The deposition of t ...

that resulted from the reaction of methane with oxygen to form carbon dioxide (a less potent greenhouse gas than methane) and subsequent depletion of atmospheric carbon dioxide by aerobic photosynthesisers * The

Sturtian The Sturtian glaciation was a Snowball Earth glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined ...

and

Marinoan The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma (million years ago) during the Cryogenian period. This glaciation possibly cove ...

Snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 M.Y.A. (million years ago) dur ...

glaciations, 715 to 680 and 650 to 632.3 million years ago, respectively, resulting from the sequestration of atmospheric carbon dioxide during the Neoproterozoic Oxygenation Event * The

Late Ordovician Mass Extinction The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 443 Mya. It ...

(LOME), to , suggested by some studies to have been caused by glaciation resulting from carbon dioxide depletion driven by the radiation of land plants *

Euxinic Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified, have an oxic, highly ...

events, such as during the

Great Dying Great may refer to: Descriptions or measurements * Great, a relative measurement in physical space, see Size * Greatness, being divine, majestic, superior, majestic, or transcendent People * List of people known as "the Great" *Artel Great (born ...

, , and the aforementioned LOME, caused by sulphur-reducing prokaryotes that produce

hydrogen sulphide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...

The list ''excludes'' the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden extinction event, mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million y ...

, since this was, at least partially, externally induced by a

meteor impact An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or ...

Current status and future extinctions

Peter Ward proposes that the current

man-made climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

and mass extinction event may be considered to be the most recent Medean event. As these events are anthropogenic, he postulates that Medean events are not necessarily caused by microbes, but by intelligent life as well and that the final mass extinction of complex life, roughly about 500–900 million years in the future, can also be considered a Medean event: Plant life that still exists then will be forced to adapt to a warming and expanding Sun, causing them to remove even more carbon dioxide from the atmosphere (which in turn will have already be due to the increasing heat from the Sun gradually speeding up the weathering process that removes them from the atmosphere), and ultimately accelerating the complete extinction of complex life by making carbon dioxide levels drop down to just 10 ppm, below which plants can no longer survive. However, Ward simultaneously argues that intelligent life such as humans may not necessarily just trigger future Medean events, but may eventually prevent them from occurring.

References

External links

* * * * * {{ExtEvent nav Events that forced the climate Earth sciences Ecological theories Evolutionary biology Extinction events Hypotheses Superorganisms Planetary science Biological hypotheses Meteorological hypotheses

Examples

Current status and future extinctions

See also

References

External links