The Big Five extinction events in Earth's history
If you are a fan of natural history, then you should be familiar with The Big Five Mass Extinction events, being the most recent and usually more popular of then, the Cretaceous-Paleogene extinction (formerly known as K-T extinction) - the one that ended the reign of the dinosaurs.
However, as the fossil record tells us, an asteroid impact is by far not the only reason life can end in a region or the entire world.
Despite being a usual phenomenon (considering geological time), there were several particularly violent mass extinction events, which killed more than half of life forms. These episodes are usually associated with the formation or division of supercontinents, that is, when in the course of continental drift several landmasses come together to form a single continent, or when it separates into others. The permo-triassic extinction, for example, occurred during the formation of the Pangea and the K-Pg extinction is associated with the opening of the Atlantic Ocean. Three extinctions, including the two largest, are associated with large areas of rocks deposited after volcanic eruptions.
Wiki has a list of major extinction events, shown bellow:
Even so, those are only the major events, extinction makes part of a natural process in which the environment changes, either by bioturbance or geological activities, and the taxa that are sensible enough cannot survive through.
The fossil record shows us that despite the changes in the world, life haven't been struck very hard since the start of the Jurassic period, and even less in events post K-Pg.
Numbers on the left indicates apparent percentage of taxa extinct in the marine life fossil record, on the bottom we have Mya, the tallest the spike, the more serious the extinction event
The exact definition of a mass extinction is arbitrary, however, we can define it as a relatively common event in the geological record that is characterized by a decrease in biodiversity through the exceptionally high extinction of several groups or, in other words, a sharp reduction in diversity and abundance of macroscopic life. This loss of diversity occurs when the rate of extinction is greater than the rate of speciation.
Since life on Earth emerged, several mass extinctions have significantly exceeded the background extinction rate. Background extinctions are extinctions that are occurring all the time, even when the rate of extinction is not very high. Thus, the observed mass extinctions are just an extreme moment of a continuation of extinction rates. All divisions of the geological time scale are marked by stratigraphic criteria that are based on the study of mass extinctions.
Mass extinction events are also responsible for the idea of Punctuated Equilibrium, that is, until rather radical changes are made to the environment, be the indirect or direct elimination of certain taxa or habitats by certain events, evolution will tend to not drive further from it's equilibrium point.
Bringing back my example from Part 2:
Imagine we have a group of colored birds, sometimes they present earthly colors, but sometimes they also present vibrant colors. For a long time, the vibrant color genes will be suppressed through natural selection, via predation from other animals.
If we somehow start a fire in this forest where they live, and it kills along with a large portion of it's population, the bird's predator - assume the birds can fly so they can flee in time - we have now removed a selective pressure from the environment.
Now, the color gene is not really a disadvantage to the species, since the colored chicks won't be predated, over time we will have a relatively large population of colored birds as this gene become more common in the population.
Now, assuming lot's of niches have been opened for these birds, like, insect eaters, fruit eaters and even predators now, the new mixed population of birds will over time diverge to avoid competition with others, filling those niches.
It is possible that, a couple, if not most of these groups will now use their new colored feathers in their mating criteria, they're easier to spot over long distances, even more among the dark soil of the forest left by the fire many years ago. Derived structures like crowns, iridescent wings or large tail plumes may arise as the competition heats, along with stronger legs and different types of beaks and feeding behaviours, some may even lose the ability to fly.
Looking at this we can see a pre-extinction stasis with earthly colored birds, a cladogenesis period where birds now invade new niches, and a post-extinction stasis with with brightly colored birds in various niches.
ASTEROID IMPACT
Artistic rendering of the Chicxulub asteroid impact
Let's properly start to build mass extinction events from the most popular method, hit by an asteroid.
Asteroid impacts can be considered rather rare, the general public may recall the Chelyabinsk meteor in 2013, the Tunguska meteor in 1908, and of course the Chicxulub meteor ~66Mya.
Meteor encounters seem to follow an inverse frequency to their size, ie, small impacts are more frequent than large impacts. As between 2001 and 2019, there have been 42 meteor encounters which blasts range between 0,1 kt and 500kt.
In 2018 alone there where 39 airbursts around the world linked to meteor events, and annually as of 2019, there are about 112 meteor showers.
Is rather improbable that one object with less than 100m in diameter may penetrate in the atmosphere enough to strike the surface and create a crater, however if the region of impact is elevated enough (+3~5km above sealevel), objects between 70m and 50m may be able to hit the surface, also depending on atmospheric density.
For reference, Little Boy - the A-Bomb dropped over Hiroshima - has a blast yield of 15kt.
Here is a table of object sizes that produce only airbursts:
And here is a table of object sizes that are able to hit the ground and create a crater:
Here is a Nukemap simulation over New York, it can only express blasts up to 100Mt, or the impact of an object between 150m and 200m wide.
And while THIS TABLE wanders only on the realm of hundreds of meters, the asteroid from the K-Pg event is estimated to have been between 11~82km, delivering over 21~921 billion Hiroshima bombs worth of energy, or about 100 million Tsar bombas upon impact (~5 petatons). Regions up to 5000km away from the ground zero were covered by 10cm of ash.
Meteor encounters seem to follow an inverse frequency to their size, ie, small impacts are more frequent than large impacts. As between 2001 and 2019, there have been 42 meteor encounters which blasts range between 0,1 kt and 500kt.
In 2018 alone there where 39 airbursts around the world linked to meteor events, and annually as of 2019, there are about 112 meteor showers.
Is rather improbable that one object with less than 100m in diameter may penetrate in the atmosphere enough to strike the surface and create a crater, however if the region of impact is elevated enough (+3~5km above sealevel), objects between 70m and 50m may be able to hit the surface, also depending on atmospheric density.
For reference, Little Boy - the A-Bomb dropped over Hiroshima - has a blast yield of 15kt.
Here is a table of object sizes that produce only airbursts:
| Impactor diameter |
Kinetic energy at | Airburst altitude |
Average frequency (years) |
Recorded fireballs (CNEOS) (1988-2018) | |
|---|---|---|---|---|---|
| atmospheric entry |
airburst | ||||
| 4 m (13 ft) | 3 kt | 0.75 kt | 42.5 km (139,000 ft) | 1.3 | 54 |
| 7 m (23 ft) | 16 kt | 5 kt | 36.3 km (119,000 ft) | 4.6 | 15 |
| 10 m (33 ft) | 47 kt | 19 kt | 31.9 km (105,000 ft) | 10 | 2 |
| 15 m (49 ft) | 159 kt | 82 kt | 26.4 km (87,000 ft) | 27 | 1 |
| 20 m (66 ft) | 376 kt | 230 kt | 22.4 km (73,000 ft) | 60 | 1 |
| 30 m (98 ft) | 1.3 Mt | 930 kt | 16.5 km (54,000 ft) | 185 | 0 |
| 50 m (160 ft) | 5.9 Mt | 5.2 Mt | 8.7 km (29,000 ft) | 764 | 0 |
| 70 m (230 ft) | 16 Mt | 15.2 Mt | 3.6 km (12,000 ft) | 1,900 | 0 |
| 85 m (279 ft) | 29 Mt | 28 Mt | 0.58 km (1,900 ft) | 3,300 | 0 |
| *Based on density of 2600 kg/m3, speed of 17 km/s, and an impact angle of 45° | |||||
And here is a table of object sizes that are able to hit the ground and create a crater:
| Impactor diameter |
Kinetic energy at | Crater diameter |
Frequency (years) | |
|---|---|---|---|---|
| atmospheric entry |
impact | |||
| 100 m (330 ft) | 47 Mt | 3.4 Mt | 1.2 km (0.75 mi) | 5,200 |
| 130 m (430 ft) | 103 Mt | 31.4 Mt | 2 km (1.2 mi) | 11,000 |
| 150 m (490 ft) | 159 Mt | 71.5 Mt | 2.4 km (1.5 mi) | 16,000 |
| 200 m (660 ft) | 376 Mt | 261 Mt | 3 km (1.9 mi) | 36,000 |
| 250 m (820 ft) | 734 Mt | 598 Mt | 3.8 km (2.4 mi) | 59,000 |
| 300 m (980 ft) | 1270 Mt | 1110 Mt | 4.6 km (2.9 mi) | 73,000 |
| 400 m (1,300 ft) | 3010 Mt | 2800 Mt | 6 km (3.7 mi) | 100,000 |
| 700 m (2,300 ft) | 16100 Mt | 15700 Mt | 10 km (6.2 mi) | 190,000 |
| 1,000 m (3,300 ft) | 47000 Mt | 46300 Mt | 13.6 km (8.5 mi) | 440,000 |
| Based on ρ = 2600 kg/m3; v = 17 km/s; and an angle of 45°; 1Mt = ~66,6x 15kt bombs | ||||
Here is a Nukemap simulation over New York, it can only express blasts up to 100Mt, or the impact of an object between 150m and 200m wide.
And while THIS TABLE wanders only on the realm of hundreds of meters, the asteroid from the K-Pg event is estimated to have been between 11~82km, delivering over 21~921 billion Hiroshima bombs worth of energy, or about 100 million Tsar bombas upon impact (~5 petatons). Regions up to 5000km away from the ground zero were covered by 10cm of ash.
Besides the obvious reasons why asteroid impacts are dangerous to life, I find hard to pinpoint where exactly it would have to hit to cause the most damage to a planet's lifeforms.
An asteroid impact on mainland is a great deal, but not so much of a disaster if all life is marine at the moment, however, it isn't really that much of a catastrophe if it hits the deep ocean like the middle of the Pacific, if only a couple shores will be affected - not to minimize things, but, a 120m tall tsunami isn't really going to wipe out 90% of life on an Africa-sized continent.
You can cause some good damage with things smaller than the moon-sized asteroid from the K-Pg event, if you know where to hit.
An asteroid impact on mainland is a great deal, but not so much of a disaster if all life is marine at the moment, however, it isn't really that much of a catastrophe if it hits the deep ocean like the middle of the Pacific, if only a couple shores will be affected - not to minimize things, but, a 120m tall tsunami isn't really going to wipe out 90% of life on an Africa-sized continent.
You can cause some good damage with things smaller than the moon-sized asteroid from the K-Pg event, if you know where to hit.
Other than Nukemap, we also have:
Crater Impact is a calculator that takes Size, Angle, Velocity and Material, to output a simulation of the impact effects at a given distance up to 500km away from the ground zero.
Data for a 5,1km rocky asteroid, at 17km/s, probing from 171km away from the impact in Portugal
Earth Impact Effects Program is my personal favorite, as it outputs a very detailed description of the series of events initiated by the impact.
Here is my rendition of the data provided by EIEP:
Here the start of the output log
It's a bright evening on a tropical array of islands, it's quiet but the sound of the wind and waves in the shallow sea.
A bright 3,2km wide asteroid have been haunting the night sky for weeks, and for the last couple days it's been visible during the day... The object entered the point of no return by the sunrise, and now it enters the upper atmosphere, in 5 seconds, it pierces through the atmosphere like it's nothing, a second sun appears to cross the sky accompanied by a continuous thunderous roaring during this brief moment. It touches the shallow waters and in less than a second it merges with the crust with a blast yield of 1,54 teratons (or 30,8 thousand Tsar Bombas detonating at once).
The ground zero is about 100 kilometers from our position, the bright object behind the horizon suddenly flashes, lighting the sky with a fireball that covers about 1/4th of the horizon, about 36 kilometers wide, 2 seconds after the flash, a wave of heat with the equivalent of 618x the usual solar radiance worth of energy - and for the next 8 minutes, the heat coming from the fireball will be intense enough to burn everything but the rock and sand that makes these islands.
20 seconds after impact, the region is shaken by an earthquake of magnitude 8,7 on the Richter scale, if there were buildings in the region, they all would have fell to the ground - at least, the ones that haven't been vaporized already.
About 2 minutes after the impact, the 24 cubic kilometers of rock vapor launched into the air cools enough to become a fine dust, enough of it to cover these islands under 4 meters of ash, rocks the size of dinner plates occasionally fall from the sky.
5 minutes after the impact, the air blast from the explosion finally arrives, the shockwave travels at whopping 2.692km/h - at mach 2,1 - the sound it makes it on the verge of ear pain at 120dB, the wall of air pulverize the water over the sea, even though it may be too hot for steam to condense in clouds, the sheer force of the blast compresses the air molecules to form a temporary dome of clouds, stripping the flaming trees off the ground - if any surviving buildings were present at the time, they would be completely flattened by now.
53 minutes after the impact, a 30m tall tsunami sweep across the region, before the sea-level retreats by dozens of meters, shoring dead marine animals in the mud formed by the wet ashes - the water retreats leaving hundreds of square kilometers of mud behind, as it flows back into the 40km wide crater, the ocean here beared about 100 meters in depth, now it has 896m in it's deepest point.
Even 500km from the ground zero, we have massive wildfires into mainland and 6m waves washing the shore, while dust and tektites fall from the sky, 1.000km from the blast and we would still have shattered windows and sand falling 10 minutes after the impact, 50 minutes before the earthquake arrives.
5.000km from the blast and a loud sound can still be heard, 10.000km from the impact a subtle breeze may kick in before pebbles occasionally start falling.
For weeks, a column of water vapor will rise from the melted crater - combined with the 62,4 billion tons of ashes launched into the atmosphere (3.210x Krakatoa's bulk eruption mass, 1,14x the volume), will make the world dip into a nuclear winter or ice age, lowering the global temperatures by several degrees, the blast itself surely disrupted the wind patterns, but in the following months, the violent recovery of equatorial currents and streams help spreading the ash globally.
To estimate the length of this cooling is hard to do - apart from asteroids, volcanic winters are linked to the release of sulfur compounds that increase Earth's albedo. - which I haven't really found data about in impact events, however, based on the amount of ash released by Krakatoa, Tambora, and Samala eruptions, the cooling effects can range anywhere between 1 and 4~5 years while the mass is suspended, leaving at least 950 thousand square kilometers covered with 4m to 2,4cm of ash on a first moment.
This is what 950.3 thousand km² look like over New York
Subsequent Fallout would make ash travel 480km up the city of Augusta in Maine by the next 24 hours (Trade winds at 20km/h)
Wind patterns of Earth would spread the ash over Greenland over a week later, reach central Europe 2 weeks later, the northern hemisphere would be covered in dust in little over 48 days, increasing Earth's albedo from usual ~32% to around 40%, the massive wildfires and nearly halving of the sunlight for the next couple years in some regions would make for quite a tragedy and probably a mass extinction event.
Talking about spreading of dust and particles in the atmosphere, we also have included in this package the
VOLCANIC / IMPACT / NUCLEAR WINTER
As of the wiki article cites:
"In the 1985 report The Effects on the Atmosphere of a Major Nuclear Exchange, the Committee on the Atmospheric Effects of Nuclear Explosions argues that a "plausible" estimate on the amount of stratospheric dust injected following a surface burst of 1 Mt is 0.3 teragrams, of which 8 percent would be in the micrometer range. The potential cooling from soil dust was again looked at in 1992, in a US National Academy of Sciences (NAS) report on geoengineering, which estimated that about 1010 kg (10 teragrams) of stratospheric injected soil dust with particulate grain dimensions of 0.1 to 1 micrometer would be required to mitigate the warming from a doubling of atmospheric carbon dioxide, that is, to produce ~2 °C of cooling."In other words, a blast charging 1 Mt is able to lift 300 million tons of dust, of which 24 million would be able to stay in suspension.
Taking into account half the content melted by the blast is thrown up in the air, we need a yield able to blast >125 million tons of material off into the atmosphere, to meet the 8% equivalent of 10 million tons of dust expected to cool the world by 2ºC.
From this perspective, using our simulated asteroid, about 4,99 billion tons of dust / soot would be able to stay suspended in the atmosphere - nearly 500x the amount needed to cause a 2ºC of global cooling as in the paper.
Considering another study from 1984:
"In 1984, the World Meteorological Organization (WMO) commissioned Golitsyn and N. A. Phillips to review the state of the science. They found that studies generally assumed a scenario where half of the world's nuclear weapons would be used, ~5000 Mt, destroying approximately 1,000 cities, and creating large quantities of carbonaceous smoke – 1–2×1014 g being most likely, with a range of 0.2–6.4×1014 g (NAS; TTAPS assumed 2.25×1014). The smoke resulting would be largely opaque to solar radiation but transparent to infrared, thus cooling the Earth by blocking sunlight, but not creating warming by enhancing the greenhouse effect. The optical depth of the smoke can be much greater than unity. Forest fires resulting from non-urban targets could increase aerosol production further. Dust from near-surface explosions against hardened targets also contributes; each megaton-equivalent explosion could release up to five million tons of dust, but most would quickly fall out; high altitude dust is estimated at 0.1–1 million tons per megaton-equivalent of explosion. Burning of crude oil could also contribute substantially.It renders us with a range of dust between 154 billion and 1,54 trillion tons of dust up in the air - of course, that's ~2,5x the amount of material we calculated previously for the bulk ejecta, because there is this point where the difference between nuclear weapons and impact events diverge from one another.
The 1-D radiative-convective models used in these studies produced a range of results, with coolings up to 15–42 °C between 14 to 35 days after the war, with a "baseline" of about 20 °C. Somewhat more sophisticated calculations using 3-D GCMs produced similar results: temperature drops of about 20 °C, though with regional variations."
In 2007, another study pointed that the release of 150 million tons of smoke would render
"A global average surface cooling of −7 °C to −8 °C persists for years, and after a decade the cooling is still −4 °C. Considering that the global average cooling at the depth of the last ice age 18,000 yr ago was about −5 °C, this would be a climate change unprecedented in speed and amplitude in the history of the human race. The temperature changes are largest over land … Cooling of more than −20 °C occurs over large areas of North America and of more than −30 °C over much of Eurasia, including all agricultural regions."And that also would reduce the global rainfall by about 45%. The effects of 50 million tons of smoke would have half the impact previously calculated, but on the same span of time, between 20 and 30 years.
That hints us about the nature of such an event, it can be described by an Exponential Decay, as shown in THIS GRAPH. Where even the halving of the effect's amplitude can actually lead to a similar spanning of time, which also explains why different volcano eruptions major effects are felt in the same span of 1~5 years.
Considering this last 2007 study as more accurate, our little asteroid lifted dust is ~33.3x more than the maximum amount calculated - resulting in 700 years 'til the mean anomaly halves, 1.3kyr until the mean anomaly go down to 1ºC, and 4,7kyr until the dust fully dissipate. Is that right?
Well, not actually, despite making some sense when put like that.
If we look at the graph more closely, we'll see that for every time we double the amount of particles, we add ~9,4 years to our covering, 33,3x is nearly as much as 5 doublings, about 5,2 doublings to be precise, what yields us +48,90 years, which puts our impact winter in about 109 years long for it to decay to 10%, and 193 years for the effects fully dissipate.
If we wanted the effects to last for about 700 years, would then need to lift up about 69 doublings of dust, or about obnoxious 2,95 sextillion times the amount put out by the Toba Supervolcano (about another 49,5 Earth masses worth of dust) , that is by the way, our next topic.
SUPER VOLCANOES
Yellowstone is a famous supervolcano (some state that it's not, but I'll put it here to be safe), is a concern for the US population, when it last erupted about 2,1Mya it expelled about 2.500km³ of ash and rock, however, it isn't the only volcano in the world that has such a massive power.
In the island of Sumatra (Indonesia), lies the Lake Toba, last time it erupted 74Kya it expelled between 2.200 and 4.400 tons of sulfuric acid summarizing about 2.800km³ of ash into the sky. Back to the US, the volcano La Garita last erupted 27,8 million years ago, launching 5.000km³ of material up in the air.
And then we have the Flat Landing Brook Formation, last erupted between 465 and 466Mya in the middle Ordovician period, probably spitting out about 12.000km³ of lava and ashes - though it is rather unclear if it was all at once in a large scale eruption or smaller eruptions over extended periods of time.
SUPER VOLCANOES
Anak Krakatau's eruption in 2018
Yellowstone is a famous supervolcano (some state that it's not, but I'll put it here to be safe), is a concern for the US population, when it last erupted about 2,1Mya it expelled about 2.500km³ of ash and rock, however, it isn't the only volcano in the world that has such a massive power.
In the island of Sumatra (Indonesia), lies the Lake Toba, last time it erupted 74Kya it expelled between 2.200 and 4.400 tons of sulfuric acid summarizing about 2.800km³ of ash into the sky. Back to the US, the volcano La Garita last erupted 27,8 million years ago, launching 5.000km³ of material up in the air.
And then we have the Flat Landing Brook Formation, last erupted between 465 and 466Mya in the middle Ordovician period, probably spitting out about 12.000km³ of lava and ashes - though it is rather unclear if it was all at once in a large scale eruption or smaller eruptions over extended periods of time.
Supervolcanoes around the world
Tectonic Plate distribution around the world
Comparing the locations of strongly volcanic active regions with plate tectonics, we see supervolcanoes can be found in regions up to ~1.000km from a tectonic meetings.
Plate general direction of movement
And comparing to the direction plates are moving, we see those supervocanoes are found where plates are colliding, in subduction zones / marine trenches.
Map of the world's subduction zones
As said before, volcanic eruptions happen to be a little more easier to compute (in my opinion) as it's major global effects depends on the amount of sulfur compounds released in the eruption.
How catastrophic it is, depends on it's bulk material (called Tephra) ejection on a logarithmic scale as a Volcanic Explosivity Index (VEI), ie a VEI 4 eruption isn't the double of a VEI 2, but actually 100x the VEI 2, and it goes on from VEI 0 - with less than 10.000m³ of flow, up to VEI 8, when the material ejection exceeds 1.000km³.
How catastrophic it is, depends on it's bulk material (called Tephra) ejection on a logarithmic scale as a Volcanic Explosivity Index (VEI), ie a VEI 4 eruption isn't the double of a VEI 2, but actually 100x the VEI 2, and it goes on from VEI 0 - with less than 10.000m³ of flow, up to VEI 8, when the material ejection exceeds 1.000km³.
The difference between a VEI 2 and a VEI 1 eruption is 100x, while between all the others it is tenfold
A couple volcanic eruptions in the VEI scale
To estimate the lenght of the cooling effect cause by the fumes and aerosols from the eruption, you can tweak the graph back in the VOLCANIC / IMPACT / NUCLEAR WINTER part.
BIOTURBATION
Bioturbations can be defined by when life forms alter the environment in such a way, it also alters which resources are available to other life forms (in most ways, it alters the sediment).
While the effects of bioturbation on the texture of a sediment are physical, the composition changes respond to chemical processes. These processes generate changes in the organic content of the sediment, concentration of trace elements, fluctuations in redox potential, flow of chemical elements, concentration of metals in the walls of the excavations and alteration of clay minerals by ingestion.
The stability of a sediment can be increased or decreased by the action of bioturbation.
One great example of a Bioturbation Extinction event is the Ordovician-Silurian Extinction, it started with the arise of terrestrial plants.
Green algae proliferated and adapted to freshwater habitats, while plants similar to mosses began to colonize terrestrial environments, which until that moment were inhabited only by lichens. These plants were still strongly linked to water, needing it for reproduction, and grew only on the banks of lakes and streams. They are known as bryophytes.
Plants like bryophytes for example, tipically fix themselves to rocks and soil, and in the process, wear down these rocks way more than the typical weathering process, releasing minerals like iron, phosphorus and potassium, releasing up to 10x more calcium, 60x more phosphorus, between 170x and 300x more iron (depending on the type of rock) than the natural weathering process.
The mineral leak increased the occurence of algal blooms, the dead algae are then decomposited by bacteria - which consumes oxygen and produces toxic byproducts, poisoning the oceans worldwide, and the consuming of CO² from the atmosphere by the land plants made the temperatures drop even more than they already were - with the moving of Gondwana further to the south - the organic carbon produced by decaying matter in the sea can't leave the water if bacteria consumed most of the free Oxygen that would turn the organic carbon in carbon dioxide, pushing the CO² side of the climatic seesaw further down.
This event marks the end Ordovician mass extinction, which decimated a considerable number of organisms, possibly caused by the arrival of the glacial period. It is estimated that 70~60% of the species have been completely extinct with changes in temperature
Ordovician-Silurian Extinction killed 70~60% of invertebrate marine life
Bioturbations can be defined by when life forms alter the environment in such a way, it also alters which resources are available to other life forms (in most ways, it alters the sediment).
While the effects of bioturbation on the texture of a sediment are physical, the composition changes respond to chemical processes. These processes generate changes in the organic content of the sediment, concentration of trace elements, fluctuations in redox potential, flow of chemical elements, concentration of metals in the walls of the excavations and alteration of clay minerals by ingestion.
The stability of a sediment can be increased or decreased by the action of bioturbation.
One great example of a Bioturbation Extinction event is the Ordovician-Silurian Extinction, it started with the arise of terrestrial plants.
Green algae proliferated and adapted to freshwater habitats, while plants similar to mosses began to colonize terrestrial environments, which until that moment were inhabited only by lichens. These plants were still strongly linked to water, needing it for reproduction, and grew only on the banks of lakes and streams. They are known as bryophytes.
Plants like bryophytes for example, tipically fix themselves to rocks and soil, and in the process, wear down these rocks way more than the typical weathering process, releasing minerals like iron, phosphorus and potassium, releasing up to 10x more calcium, 60x more phosphorus, between 170x and 300x more iron (depending on the type of rock) than the natural weathering process.
"All plants require rock-derived minerals — including phosphorus, potassium, calcium, magnesium and iron — for growth. Land plants have evolved a variety of systems and symbiotic relationships that accelerate the release of these essential nutrients from rocks"Over time, as plants build up the soil on land, the phosphorus leaked onto the sea, and by the time plants learned how to recycle phosphorus in the land substrate, it and other minerals have already been leaking into the waters for millions of years, and the appearance of vascular plants later created a second peak in rock weathering.
The mineral leak increased the occurence of algal blooms, the dead algae are then decomposited by bacteria - which consumes oxygen and produces toxic byproducts, poisoning the oceans worldwide, and the consuming of CO² from the atmosphere by the land plants made the temperatures drop even more than they already were - with the moving of Gondwana further to the south - the organic carbon produced by decaying matter in the sea can't leave the water if bacteria consumed most of the free Oxygen that would turn the organic carbon in carbon dioxide, pushing the CO² side of the climatic seesaw further down.
This event marks the end Ordovician mass extinction, which decimated a considerable number of organisms, possibly caused by the arrival of the glacial period. It is estimated that 70~60% of the species have been completely extinct with changes in temperature
Human activity have been found to be a major contributor to the extinction of several megafauna like many species of mammoths
The Holocene extinction is the one we are currently living in, on a world scale, occurring during the modern geological era of the Holocene. The large number of extinctions covers numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; many of which are in tropical forests. This mass extinction is sometimes called the sixth extinction, as it follows the previous five, which occurred in the last 420 million years.
During the last century, between 20.000 and 2 million species have become extinct, but the total number cannot be determined more precisely within the limits of current knowledge. Up to 140.000 species per year may be the current rate of extinction, based on the estimated upper limit.
In a broad sense, the Holocene mass extinction includes the remarkable disappearance of large mammals, known as megafauna, at the end of the last glaciation, 9.000 to 13.000 years ago. Such disappearances have been considered either as a response to climate change, the result of the proliferation of modern humans, or both.
These extinctions, which occurred near the Pleistocene-Holocene limit, are sometimes referred to as Pleistocene mass extinctions or Ice Age mass extinctions. However, the Holocene's mass extinction continues through the past several millennia and includes the present time.
PLATE TECTONICS
The world's ever changing climate is a major player for 3 of the Big Five mass extinctions, the late Devonian extinction, the Capitanian mass extinction, the Permian-Triassic extinction, and the Triassic-Jurassic extinction.
Be it the flooding of large plains, the desertification of massive forests, or the freezing of an entire continent, the weather itself plus the volcanic activity from changing tectonic plates have the potential to cause several extinctions of entire groups of animal life.
Climatic changes are driven by both biotic and abiotic factors, and usually take place in geological timescales, however it is still responsible for being a major motor of evolution itself.
AFTERMATH OF A MASS EXTINCTION
Many times, extinction is what drives evolution, and as we've seem so far, it can also be the other way around.
We are somewhat used to think of the Tree of Life, as this continuously branching tree, ever growing and ever accumulating diversity - except, the fossil record doesn't tell us that - we've seem dozens of animal families disappear from the fossil record, and who knows which ones weren't preserved for us to observe their rise and downfall.
We see the Tree of Life bears these various scars and broken branches, many families and life forms seem to be mere flashes as the ages go by, while other more resilient life forms manage to persist, but only so much further as their ability to adapt go.
Life will naturally try to overcome adversity over time, but when it strikes too fast, it can't keep up, and many groups get affected and eventually die out as result - and the whole point of Life's genetic diversity is to even though an asteroid wipes out 90% of life, that last bit haves it enough to rebuild it.
This when I like to remember this amazing video about bacteria adapting to different concentrations of antibiotics, as the amount of resources goes through a dip, we see different strains of bacteria arising to accomplish the same objective - survive.
We can see a similar view to that in the opening of this part, and also in the image bellow:
The above graph shows mammal diversity over time from the end Triassic to Present day, and although there were many successful clades of mammals, there were as much many not-so-successful ones, either via over-adaptation to certain environments that eventually faded out as result of natural climate changes or cosmic events like an asteroid impact, or the appearance of one or more clades that happened to be more adapted to one's task.
Is kind of a mess to try stipulate how serious are potential extinction events - I bring back the example of asteroid impacts in early Earth, as it would be considerably nasty if happened today, or, a few million years ago, but wouldn't be so much if happened back in the Archean Eon as microbes are incredibly resilient and fragile in their own way, similar aspects of our species as well, as we are able to live in harsh environments if properly equipped, but Earth's oxygen levels can't drop in more than 1% - or we all suffocate, all life is resilient and fragile in their own way.
And if mass extinctions are somewhat part of the natural world you've built so far, is very important to analyze and make predictions as to what organisms are more likely to survive, in which new conditions, and new environments are about to come in the aftermath of it.
Adaptative radiation opens windows to several new perspectives about life and it's many solutions, but we shall be aware that there will be always exist certain rules that apply for certain biological constraints, as I have cited before:
During the last century, between 20.000 and 2 million species have become extinct, but the total number cannot be determined more precisely within the limits of current knowledge. Up to 140.000 species per year may be the current rate of extinction, based on the estimated upper limit.
In a broad sense, the Holocene mass extinction includes the remarkable disappearance of large mammals, known as megafauna, at the end of the last glaciation, 9.000 to 13.000 years ago. Such disappearances have been considered either as a response to climate change, the result of the proliferation of modern humans, or both.
These extinctions, which occurred near the Pleistocene-Holocene limit, are sometimes referred to as Pleistocene mass extinctions or Ice Age mass extinctions. However, the Holocene's mass extinction continues through the past several millennia and includes the present time.
PLATE TECTONICS
The world can be a harsh place sometimes, and sometimes it's not, who knows?
The world's ever changing climate is a major player for 3 of the Big Five mass extinctions, the late Devonian extinction, the Capitanian mass extinction, the Permian-Triassic extinction, and the Triassic-Jurassic extinction.
Be it the flooding of large plains, the desertification of massive forests, or the freezing of an entire continent, the weather itself plus the volcanic activity from changing tectonic plates have the potential to cause several extinctions of entire groups of animal life.
Climatic changes are driven by both biotic and abiotic factors, and usually take place in geological timescales, however it is still responsible for being a major motor of evolution itself.
AFTERMATH OF A MASS EXTINCTION
Where the width of the purple bar indicates the biodiversity in the group, notice there is several bottlenecks / tightenings of the bars
Many times, extinction is what drives evolution, and as we've seem so far, it can also be the other way around.
We are somewhat used to think of the Tree of Life, as this continuously branching tree, ever growing and ever accumulating diversity - except, the fossil record doesn't tell us that - we've seem dozens of animal families disappear from the fossil record, and who knows which ones weren't preserved for us to observe their rise and downfall.
Diversification after an Extinction event
We see the Tree of Life bears these various scars and broken branches, many families and life forms seem to be mere flashes as the ages go by, while other more resilient life forms manage to persist, but only so much further as their ability to adapt go.
Life will naturally try to overcome adversity over time, but when it strikes too fast, it can't keep up, and many groups get affected and eventually die out as result - and the whole point of Life's genetic diversity is to even though an asteroid wipes out 90% of life, that last bit haves it enough to rebuild it.
This when I like to remember this amazing video about bacteria adapting to different concentrations of antibiotics, as the amount of resources goes through a dip, we see different strains of bacteria arising to accomplish the same objective - survive.
The beautiful but terrifying exposing of the evolutionary dynamics behind antibiotic resistance
We can see a similar view to that in the opening of this part, and also in the image bellow:
Note the rise of mammals by the K-Pg boundary
The above graph shows mammal diversity over time from the end Triassic to Present day, and although there were many successful clades of mammals, there were as much many not-so-successful ones, either via over-adaptation to certain environments that eventually faded out as result of natural climate changes or cosmic events like an asteroid impact, or the appearance of one or more clades that happened to be more adapted to one's task.
Is kind of a mess to try stipulate how serious are potential extinction events - I bring back the example of asteroid impacts in early Earth, as it would be considerably nasty if happened today, or, a few million years ago, but wouldn't be so much if happened back in the Archean Eon as microbes are incredibly resilient and fragile in their own way, similar aspects of our species as well, as we are able to live in harsh environments if properly equipped, but Earth's oxygen levels can't drop in more than 1% - or we all suffocate, all life is resilient and fragile in their own way.
And if mass extinctions are somewhat part of the natural world you've built so far, is very important to analyze and make predictions as to what organisms are more likely to survive, in which new conditions, and new environments are about to come in the aftermath of it.
Adaptative radiation opens windows to several new perspectives about life and it's many solutions, but we shall be aware that there will be always exist certain rules that apply for certain biological constraints, as I have cited before:
"Not all creatures retain the same evolutionary plasticity."
The Night Stalker (???)
From the book, After Man: A Zoology of the Future
- M.O. Valent, 15/06/2020
