The Medea hypothesis is a term coined by

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Peter Ward for a hypothesis that contests the Gaian hypothesis and proposes that multicellular life, 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 ...

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

Medea In Greek mythology, Medea (; ; ) is the daughter of Aeëtes, King Aeëtes of Colchis. Medea is known in most stories as a sorceress, an accomplished "wiktionary:φαρμακεία, pharmakeía" (medicinal magic), and is often depicted as a high- ...

(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 fall in the diversity and abundance of multicellular organisms. It occ ...

result in returns to the microbial-dominated state Earth has been in 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) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, was a time interval during the Earth's Paleoproterozoic era when the Earth's atmosphere an ...

, 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 at least three ice ages occurred during the deposition of the Huronian Supergroup. Deposition of this largely sedimentary succession extended from approximately 2.5 to 2.2&n ...

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 and Marinoan

Snowball Earth The Snowball Earth is a historical geology, geohistorical hypothesis that proposes that during one or more of Earth's greenhouse and icehouse Earth, icehouse climates, the planet's planetary surface, surface became nearly entirely freezing, fr ...

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 445 mill ...

(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 wikt:anoxic, anoxic and wikt:sulfidic, 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 strat ...

events, such as during the Great Dying, , 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 toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist Ca ...

The list ''excludes'' the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...

, 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 been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effe ...

Current status and future extinctions

Peter Ward proposes that the current

man-made climate change Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

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 been lowered due to the increasing heat from the Sun gradually speeding up the weathering process that removes these molecules 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 Biological hypotheses Earth sciences Ecological theories Events that forced the climate Evolutionary biology Extinction events Hypotheses Medea Meteorological hypotheses Planetary science Superorganisms Words and phrases derived from Greek mythology

Examples

Current status and future extinctions

See also

References

External links