End-Permian Extinction (EPE)

300-200 mya 300-250mya Permian 250-200 Triassic

The Permian Period ended as perhaps the worst extinction in earth’s history. In the EPE up to 95 percent of all known sea creatures were wiped out, as were 70 percent of terrestrial animals, although there is now doubt about any decline in plants (Nowak et al 2019) and a possible increase in fungi - feeding on the dead stuff (Visscher et al 1996). University of Bristol palaeontologist Michael Benton wrote the book about it called “When life nearly died.” But somehow soil survived.

What led to the great End Perminan Extinction (EPE)?

The catastrophe bringing about the end of the Permian is hotly debated. When I say hotly, that is because some blame global cooling, while the more popular version these days is of massive volcanic eruptions over nearly a million square miles in Siberia, thus reducing oxygen but increasing carbon dioxide – bringing on global warming.

The "role of enhanced UV irradiation linked to volcanism-induced disruption of the ozone shield" has now been demonstrated (Li et al 2024)

This massive eruption of the Siberian flood basalts generated excessive emissions of thermogenic methane and CO2. Clouds of volcanic ash may have restricted the amount of sunlight available, thereby inhibiting photosynthesis by plants, lowering the extraction rate of carbon dioxide and the emission of oxygen.

The clouds of volcanic ash led to the ignition of large coal seams and burnt forests. The trees collapsed, but perhaps also because of fungal attack .re killed.

Fungal death

It may also have been that trees which became less healthy were susceptible to virulent fungi leading to widespread devastation of arboreal vegetation. “Throughout the world, latest Permian records of organic-walled microfossils are characterized by the common presence of remains of filamentous organisms, usually referred to the palynomorph genus Reduviasporonites…which resemble Rhizoctonia, a modern complex of soil-borne filamentous fungi that includes ubiquitous plant pathogens”(Visscher et al 2011)

Palynomorphs

https://www.science.org/doi/10.1126/sciadv.ads5614

Could Palynomorphs be bridge between crusts and soil and give rise to lichens?

A "sill" refers to a subsurface magma intrusion that, instead of erupting onto the surface, spread out beneath the Earth's shallow crust, heating carbon-rich sediments and releasing massive amounts of greenhouse gases, likely contributing to the extinction event.

Connection between Sills & Evaporates

The interaction between sills (from the Siberian Traps volcanic activity) and evaporite deposits was a key factor in amplifying the environmental disaster. As sills intruded into evaporite-rich basins, the heat caused the release of massive amounts of greenhouse gases, sulfur gases, and halogens, which led to global warming, acid rain, ozone depletion, and ocean acidification. These environmental stressors played a major role in driving the extinction of a vast majority of species on Earth at that time.

Siberian Traps and Magmatic Activity:
- The Siberian Traps, a large igneous province in present-day Russia, were responsible for vast volcanic eruptions during the End-Permian extinction. These eruptions included both lava flows and the intrusion of sills into the surrounding sedimentary layers, including evaporite-rich basins.
- The emplacement of sills into evaporite deposits released large amounts of toxic gases and greenhouse gases, including CO2, methane (CH4), hydrogen chloride (HCl), and sulfur dioxide (SO2). This release of gases had a devastating impact on the climate and atmosphere.
Evaporites as a Source of Toxic Gases:
- When the hot magma from the sills intruded into the evaporite layers, it caused thermal decomposition of the evaporites. The heat broke down the sulfur- and chlorine-rich minerals, releasing significant quantities of chlorine and sulfur compounds into the atmosphere.
- Sulfur dioxide (SO2), when released in large quantities, contributed to acid rain and atmospheric cooling through the formation of aerosols. These aerosols would have blocked sunlight, causing temporary cooling, but the large-scale release of CO2 ultimately led to global warming.
- Chlorine (Cl2) and other halogen gases, like hydrogen chloride (HCl), likely contributed to the destruction of the ozone layer, increasing ultraviolet (UV) radiation reaching Earth's surface, which could have further damaged ecosystems.
Climate and Environmental Impacts:
- The combination of greenhouse gases (like CO2 and methane) and aerosols from evaporite decomposition resulted in rapid climate changes, including initial cooling followed by extreme global warming. This created a "hothouse Earth" scenario, with temperatures rising dramatically, which placed immense stress on both marine and terrestrial life.
- Acid rain and increased UV radiation due to ozone depletion would have directly harmed land plants and disrupted food chains, while ocean acidification (caused by CO2 dissolving in water) severely affected marine organisms, particularly those with calcium carbonate shells (e.g., corals, brachiopods).

"Thermal modeling shows that the intrusion of a sill of a few tens of meters thickness, active over timescales of a few years, causes the evaporites surrounding the sill to become depleted in halogens through devolatilization, whereby heating drives off water and halogens partition into a hot aqueous fluid. At low pressures in the crust, where we envisage much of the sill emplacement to have occurred, phase separation into a low-density vapor and a higher density brine would occur. Basaltic magmas in the sill may assimilate such brines, becoming enriched in halogens. Vapor-transported halogens may have been outgassed to the atmosphere (via pipes or a permeable fracture network). These mechanisms of magmatic halogen assimilation from evaporites have implications for the amounts of Br and Cl reaching the atmosphere during both intrusive (whereby magmatism is dominated by sill emplacement) and extrusive activity (dominated by surface lavas flows)." (Sibik et al 2021)

Sills & Evaporites

A sill is a particular type of, usually, shallow igneous intrusion following horizontal and sub horizontal planar weaknesses in the crust, typically along 'bedding planes', and other planar features, often between layers of sedimentary and metamorphic rock, and occasionally between layers of igneous rock

Evaporites are sedimentary rocks that form from the evaporation of saline water, commonly in arid environments. Common evaporite minerals include halite (rock salt), gypsum, and anhydrite. They are rich in sulfur and chlorine.

Halogens

The environmental impact of 'halogens' had significant effects on the atmosphere and oceans. The release of halogen-rich gases, acid rain, and the reduced plant cover, would have contributed to the global environmental stresses driving the EPE and contribute to ozone layer depletion. increasing UV radiation on the Earth's surface, and further stressing both terrestrial and marine ecosystem.
This would have compounded the already severe environmental stresses and reduced terrestrial biodiversity further.

"The halogens, along with other volatiles that were released into the atmosphere during these eruptions, likely caused a near to total loss of global ozone, which then increased UV-radiation. As a result, there was a massive increase in mutation and sterilization in organisms."

Volatile halogenated hydrocarbons from a huge salt lake could have helped wipe out life on Earth 250 mya (Weissflog et al 2009)

Halogen impacts on soil
This huge increase in halogen concentrations in the surface environment had several significant implications for soils.

1. Soil Contamination by Halogens:

Release of Halogens (Br and Cl): As the sills intrude and heat the evaporites, halogens such as bromine (Br) and chlorine (Cl) are released into the surrounding environment. At low pressures typical of the upper crust, these halogens can become part of a low-density vapor or a high-density brine.
Outgassing to the Atmosphere: The vapor phase, rich in halogens, could be transported through volcanic pipes or fracture networks and released into the atmosphere. This release would have led to significant contamination of the soils through acid rain or direct deposition of halogen-rich aerosols.

2. Acidification and Chemical Weathering of Soils:

Acid Rain Formation: The outgassed halogens, especially chlorine and bromine, could react with water vapor in the atmosphere to form hydrochloric (HCl) and hydrobromic (HBr) acids. When these acids precipitate as acid rain, they would significantly lower the pH of the soil. This acidification would lead to an increase in the weathering of soil minerals, leaching nutrients such as calcium, potassium, and magnesium from the soils, and rendering them less fertile.
Dissolution of Soil Minerals: Acidified soils would promote the dissolution of primary minerals, especially carbonates and feldspars. The leaching process could remove essential plant nutrients, affecting plant growth and leading to a collapse in the terrestrial ecosystem.

3. Destruction of Soil Organic Matter:

Impact on Soil Microbiota: The sudden increase in soil acidity and the presence of toxic halogens could destroy much of the soil's organic matter and beneficial microorganisms. This would reduce the capacity of soils to support plant life and other organisms dependent on healthy soil conditions, further stressing the terrestrial ecosystem.
Reduction in Decomposition Rates: With disrupted microbial communities, the rates of organic matter decomposition would likely decrease, affecting nutrient cycling and carbon sequestration in the soils.

4. Physical Changes in Soil Structure:

Disruption from Thermal Processes: The thermal impact of sill intrusion can cause localized heating of soils and rocks, potentially altering soil structure by expanding and fracturing mineral grains, thereby affecting porosity and permeability.
Release of Volatiles and Heat: The heat generated by magmatic activity can cause soil desiccation, reducing moisture content and potentially creating more arid conditions, especially in regions near active sills.

5. Increase in Toxic Elements in Soil:

Enrichment of Halogens in Soils: The assimilation of halogen-rich brines by basaltic magmas and their subsequent emplacement or eruption can introduce high levels of toxic elements (e.g., chlorine, bromine) directly into soils. Elevated halogen concentrations can be toxic to plant life and reduce soil fertility.
Deposition of Ash and Volcanic Particulates: The presence of extrusive volcanic activity (surface lava flows) could deposit large amounts of volcanic ash rich in halogens and other elements onto soils, further contaminating them.

Crusts

After the EPE, the land surface would have undergone dramatic changes due to extreme environmental stress, including severe climate shifts, deforestation, soil degradation, and increased erosion extensive aridification, and volcanic activity. The Environmental Conditions Contributing to Crust Formation were

Deforestation and soil erosion: With widespread loss of plant life due to the mass extinction, soils were left unprotected, leading to severe erosion and deposition of fine materials, which could later form crusts.
Volcanism and greenhouse warming: The intense volcanic activity from the Siberian Traps injected massive amounts of CO2, SO2, resulting in warming, coupled with aridification, would have driven crust formation through processes like evaporation and mineral precipitation.
Extreme aridity: Large parts of Pangaea became highly arid following the extinction, a perfect setting for the formation of evaporitic crusts and mineral hardpans.

These crusts would have included desert pavements, salt crusts, calcrete, silcrete, biological soil crusts, ferricrete, and gypsic crusts. They played an important role in stabilising barren landscapes and influencing the slow recovery of terrestrial ecosystems....see more

1. Desert Pavements (Stone Crusts):

With the loss of vegetation, vast areas of land became more prone to desertification and erosion, especially in the arid regions of Pangaea. This would have exposed large amounts of bare soil and rock fragments.
Desert pavements are a type of stone crust formed by wind and water erosion removing finer sediments and leaving behind a layer of coarse, tightly packed pebbles or stones on the surface. These pavements stabilize the surface, reducing further erosion.

2. Salt Crusts (Evaporitic Crusts):

With the intense aridification that followed the extinction, some areas—especially in low-lying basins—may have experienced the formation of salt crusts or evaporite crusts.
As lakes and inland seas evaporated due to extreme heat, they would leave behind concentrated salts, like halite (rock salt) and gypsum, forming hard, crusty surfaces.
These crusts are common in today's desert playas (dry lake beds) and could have formed in similar environments in the aftermath of the Permian extinction.

3. Calcrete (Calcium Carbonate Crusts):

Calcrete (or caliche) forms when calcium carbonate (CaCO3) precipitates from groundwater or surface waters and accumulates in soil or sediment. It creates a hard, cemented layer that often forms in semi-arid to arid regions.
Following the Permian extinction, high levels of carbon dioxide in the atmosphere (from volcanic outgassing and decaying organic material) could have led to increased dissolution of calcium from weathering rocks, which would then precipitate as calcium carbonate crusts in areas with sufficient evaporation.
Calcrete can develop as a thick, hard crust on the land surface, limiting plant growth and altering the hydrology of the landscape.

4. Silica Crusts (Silcrete):

Silcrete is a type of crust formed by the cementation of soil and sediment with silica (SiO2), usually under intense evaporation conditions. Silcrete is very hard and resistant to erosion and typically forms in areas with limited vegetation and fluctuating wet and dry periods.
In the aftermath of the End-Permian extinction, such conditions might have existed in some parts of Pangaea, particularly in arid or semi-arid regions, where silica-rich groundwater could have cemented the surface layers of soil into a hard crust.

5. Biological Soil Crusts (Microbial or Cyanobacterial Crusts):

After the collapse of ecosystems, particularly plant life, biological soil crusts formed by microbes (like cyanobacteria, fungi, algae, and lichens) could have become prevalent. These crusts form when microorganisms colonize and stabilize the soil surface, creating a protective layer that helps reduce erosion and retain moisture.
In the early Triassic period, when land ecosystems were struggling to recover, biological soil crusts might have played a significant role in stabilizing the landscape, especially in barren or marginal environments where higher plants had not yet re-established.

6. Iron Crusts (Ferricrete):

Ferricrete is a type of crust formed by the precipitation of iron oxides in soils or sediments, often in areas with fluctuating wet and dry conditions. It creates a reddish, hard layer that cements the soil particles together.
Following the End-Permian extinction, regions with exposed soils and fluctuating water tables could have experienced the formation of iron-rich crusts due to the weathering of iron-bearing rocks, contributing to the reddish color seen in some Permian and Triassic sedimentary layers.

7. Gypsic Crusts (Gypsum Crusts):

In regions where evaporite minerals were present (e.g., after evaporative concentration of saline waters), gypsic crusts could have formed. Gypsic crusts are rich in gypsum (CaSO4·2H2O) and tend to form in arid or semi-arid environments where evaporation exceeds precipitation.
These crusts could have developed in areas where evaporite deposits, formed during earlier Permian periods, were exposed and weathered after the extinction event.

The answer to this question may be the most important explanation of how our planet has such complex life following this 'extinction'.

How did the soil react with these crusts?

Soils in the aftermath of the EPE likely interacted dynamically with surface crusts, driven by the slow recovery of biological activity and environmental factors. Biological soil crusts played a major role in stabilising soils, while calcrete and silcrete provided physical challenges that were gradually broken down by chemical weathering and microbial action. The absence of earthworms and higher oribatids was compensated for by microbial decomposers, small arthropods like springtails, lower oribatids and symphylans, along with symbiotic fungi, allowing soils to slowly rebuild their structure and fertility over time. This process was critical to the eventual recovery of Earth's ecosystems, as soils became more capable of supporting plant, animal and microbial life, which in turn created feedback loops that facilitated further soil development and ecosystem stability.

The interaction between soils and crusts during the aftermath of the EPE is crucial to understanding how Earth's ecosystems managed to recover from such an extreme event. Despite the mass extinction, Earth's soils still exhibited good decomposition and supported some biological activity. Here's how soils, lacking earthworms and higher oribatid mites (key decomposers today), would have interacted with the various crusts that formed:

1. Biological Activity in Permian Soils (Post-Extinction)

Even without earthworms and higher oribatids (which are critical today for soil aeration and organic matter breakdown), soil ecosystems still had other life forms:

Microorganisms: Bacteria, fungi, and cyanobacteria were already well-established decomposers by the Permian. They played a critical role in breaking down organic matter and facilitating nutrient cycling.
Lower Oribatid Mites and Nematodes: Although higher oribatid mites (important detritivores) weren't present, lower oribatid mites and nematodes were still active in the soils. These small invertebrates contributed to soil health by feeding on decaying organic material and microorganisms.
Plants and Fungi: Early Triassic flora, including pioneering plants like ferns, lycophytes, and other spore-producing plants, would have slowly recolonized the land. These plants had symbiotic relationships with fungi (like mycorrhizae), which helped to increase soil fertility and organic matter.

Despite the absence of modern-day soil engineers like earthworms, these organisms allowed the soil to maintain some level of decomposition and biogeochemical cycling.

2. Interaction Between Soils and Crusts

In the post-extinction landscape, soils had to deal with various types of crusts, such as salt crusts, calcrete, silcrete, and biological crusts. The interaction between these crusts and soils would have been dynamic and shaped how ecosystems recovered:

a. Biological Soil Crusts and Soil Stabilization:

Biological soil crusts formed by microorganisms like cyanobacteria, lichens, and fungi would have been crucial in stabilizing soils, especially in areas where plant life had been decimated. These crusts acted as protective layers, reducing wind and water erosion.
By protecting the soil surface, biological crusts would have enabled the slow recolonization of plants, allowing early pioneering species to establish root systems without losing too much topsoil. As plants grew and decomposed, they added organic matter to the soil, helping to create a more fertile and stable environment.

b. Interaction with Calcrete and Silcrete:

Calcrete and silcrete crusts, being hard, mineralized layers, would have created physical barriers for soil organisms and plant roots. In areas where these crusts were prevalent, the recovery of soil ecosystems would have been slower.
However, cracking in these crusts, due to temperature fluctuations or mechanical weathering, might have allowed some organic material and microorganisms to infiltrate, slowly breaking down the crusts over time.
Fungi and bacteria, which can secrete organic acids, would have contributed to the chemical weathering of calcrete and silcrete, helping to break them down and freeing minerals that plants could use. This process would have been slow but would have gradually improved soil fertility beneath these crusts.

c. Salt Crusts and Soil Salinization:

In areas where salt crusts (evaporite deposits like halite and gypsum) formed, soil salinization would have been a major issue. Salt crusts can inhibit plant growth and reduce microbial activity by increasing soil salinity.
Certain salt-tolerant microorganisms and possibly some halophytic plants (salt-tolerant plants) might have been able to colonize these areas, gradually introducing organic matter to the soil. This slow buildup of organic material could have helped reduce salinity over time as plant roots and microorganisms broke up the salt crusts, promoting better water infiltration and leaching of salts from the soil.
As more organic matter accumulated, the development of organic-rich soils (even in salty conditions) could have promoted microbial activity and early plant growth, setting the stage for more complex ecosystems.

d. Acid Rain and Chemical Weathering:

The acid rain produced by volcanic outgassing during the Siberian Traps eruptions would have played a significant role in the chemical weathering of mineral crusts, particularly calcretes and ferricretes. Acidic precipitation could break down calcium carbonate and iron oxides in these crusts, making nutrients like calcium and iron more available for plant uptake.
This chemical weathering process might have helped soils regain mineral balance and created more favorable conditions for the recolonization of plants and microbial communities, despite the tough environmental conditions.

e. Erosion, Transport, and Soil Formation:

In areas where the crusts were thin or broken by mechanical and chemical processes, they could have been further fragmented and eroded by wind and water. This would lead to the deposition of fine particles (like clays and silts) in other areas, helping to form new soil horizons.
These transported sediments could mix with organic material from decomposing plants and microorganisms, leading to the formation of new, fertile soils in areas that were previously barren.

3. Soil Recovery and the Role of Organic Matter:

Organic matter from the slow recolonization of plants and microbial decomposition would have been critical in soil recovery. As pioneer plants like ferns and lycophytes established themselves, they would have contributed organic residues to the soil, building humus.
Humus helps bind soil particles together, retains moisture, and provides essential nutrients for plants. Over time, the accumulation of organic material in the soil would have increased its capacity to support life, enabling more complex plants and soil organisms to return.

4. Nutrient Cycling Without Earthworms and Higher Oribatids:

Even without the bioturbation (mixing of soils by organisms) provided by earthworms or the advanced detritivory of higher oribatid mites, decomposition processes would have continued through microbial breakdown and the activity of lower invertebrates (e.g., nematodes and simple mites). Microorganisms played a major role in:

Breaking down dead plant material.
Cycling nutrients, especially nitrogen and phosphorus, that would have been critical for soil fertility.
Facilitating the recovery of plants that depended on these nutrients to grow in the post-extinction environment.

And what role may lichens have played in this?

What role did soil play in maintaining life ever after?
The single continent of Pangea housed all that was needed
We shall see in the next Period - Triassic.

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