siberian traps

WHERE DO MAMMALS COME FROM?

The Earth plays host to a remarkable variety of creatures all of which diverged from a single, unknown common ancestor. In the 540 million year history of complex life there have been repeated turnovers in dominant life forms, from The Age of Fishes during the Devonian to The Age of Reptiles during the Mesozoic which gave way to our current era in time, the Cenozoic, or otherwise known as The Age of Mammals. But where do mammals come from…?

Pelycosaurs…
The Pelycosaurs first appeared 306Ma and are the most basal synapsids. Synapsids are mammal-like reptiles; a distinguishable feature is their skull with only one post orbital fenestra, reptiles have two. The mammal-like reptiles show the earliest signs of evolution towards more mammal characteristics, Dimetrodon is a classic example. Dimetrodon had only a single temporal fenestra, this feature allowed for jaw muscle attachment to be further back providing a stronger bite force over a wider range of jaw movements, subsequently making Dimetrodon one of the most successful predators of its age.
Dimetrodon quite literally means “two sets of teeth” and this refers to its elongated incisors, this is the beginnings of the mammal feature known as heterodonty (differentiated teeth). Dimetrodon also exhibits deep ridges of the inner nasal cavity providing a larger surface area for the attachment of olfactory epithelium indicating a larger reliance of the sense of smell (something that will become more important in future mammal evolution).

Therapsids…
Therapsids appear around 275Ma and likely evolved from pelycosaurs or a similar sort of ancestor. They are still classed as synapsids but they even more mammal-like features than their ancestors. Therapsids have less of a sprawling gait than the pelycosaurs and other reptiles (although the herbivorous kind still retain a rather sprawling gait, this is a feature that is slow to disappear). Therapsids have an even larger temporal fenestra and more elongated incisors as the teeth continue to differentiate. The skull of therapsids is also beginning to change; mammals have a single jaw bone called the dentary, this is present in synapsids along with many other jaw bones such as the quadrate and articular, but as mammal evolution gets underway the dentary expands and the quadrate and articular reduce in size and become part of the middle ear bones. Some Therapsids were apex predators throughout the permian such as Gorgonops.

Cynodonts…
Cynodont fossils are some of the most important fossils in the mammals evolutionary record and we are classed as part of Cynodontia. They are dog-like creatures and appear around 260Ma, they were hugely successful and diversified rapidly. One of the best examples of cynodonts in mammal evolution is Thrinaxodon. The cynodonts exhibit even greater tooth differentiation and tooth occlusion (precise tooth contact of the upper and lower teeth, a feature unique to mammals). Tooth occlusion also suggests the cynodonts had controlled tooth replacement like mammals (mammals exhibit diphyodonty meaning two sets of teeth, the milk teeth and the adult teeth).
More importantly, cynodonts also show partial or complete secondary palates meaning they are able to swallow food and breathe at the same time, something reptiles cannot do. Many taxa also show absence of abdominal ribs allowing for the presence of a diaphragm which increased lung capacity. A diaphragm paired with the secondary palate and tooth occlusion suggests that cynodonts had a higher metabolism than other extant animals of the time. The cynodonts dentary continues to expand further back of the skull.
Some cynodont skulls have small indentations around the nasal region which may be indicative of nerve passages towards sensitive hairs, possibly whiskers, if so, cynodonts had hair. Thrinaxodon and others also have a larger brain size in comparison to the rest of the body than other animals as well as enlarged auditory and olfactory regions suggesting they were nocturnal.

The Permian extinction struck 250Ma due to extensive volcanism of the Siberian Traps leading to a runaway greenhouse effect. Between 80% and 96% of living species died out, including most of the cynodonts and the therapsids. Reasons why the reptiles battled through this extinction and rose to dominate is still debated but it may be due to the fact that reptiles can secrete nitrogenous waste as a uric paste whereas mammals must secrete is as a liquid. This allowed the reptiles to conserve water and see the extinction through.
Whilst most cynodont species perished, a few individuals made it through, they were mostly small, nocturnal burrowers capable of getting water from underground root nodules and tubers. However, the cynodonts would not rise to dominance again but their descendants would, although not for another 200 million years. They would spend the Mesozoic Era in the dinosaurs shadows, their evolution driven by a nocturnal lifestyle and the need for endothermy. The evolution of our ancestors was shaped by the dominance of the dinosaurs, when their reign ended 65 million years ago our true mammalian ancestors would quickly take over the niches left behind and become some of the most spectacular creatures the world has ever seen.

onecornflower  asked:

I've always wondered... In the Permian (and other epochs?) the oxigen-levels were super high, right? Which is why the arthropods grew to enormous sizes. But where did all the oxigen go? Where is it today?

Yes! Atmospheric oxygen was at an all-time high during the Carboniferous and the Permian, and has been linked to large body sizes in arthropods, particularly terrestrial insects. One suggestion for why high oxygen results in large body sizes in insects is because body size is limited by the size of the tracheal system, which is influenced by the amount of oxygen in the air. Alternatively, it has also been suggested that oxygen poisoning mean that insect larvae needed to grow quickly in order to survive (however note that in the literature there isn’t much of a consensus of the causes of C-P arthropod gigantism).

By the end of the Permian, oxygen dramatically decreased (good-bye, giant arthropods), likely the result of increased volcanism. Volcanism in the Siberian Traps is often cited as a cause of the End Permian mass extinction. In short, such volcanism uses up oxygen to produce volcanic gases such as carbon dioxide, sulphur dioxide and water vapour (i.e. greenhouse gases, causing global warming and therefore the extinction event). So all the oxygen was reworked into other compounds.  

I hope that answered your question! I have a heap of other giant arthropods planned for future posts (like more giant sea scorpions and larger trilobites) so I might in future do a full-on post about gigantism in the late Palaeozoic, cos there are some really interesting papers discussing the causes. 

Azrael has lived through the creation and break-up of seven supercontinents before the geology of modern-day Earth. Vaalbara, Kenorland, Paleopangea, Columbia, Rodinia, Pannotia and Pangea. 

She has lived through five mass extinctions. 

1.) The Ordovician–Silurian Extinction,  439 million years ago, in which 86% of life on Earth was wiped out by falling temperatures. 

2.) The Late Denovian Extinction, 364 million years ago, in which 75% of life on Earth was wiped out by a lack of oxygen in the seas and volcanic ash causing another drop in temperatures.

3.) The Permian-Triassic Extinction (The Great Dying), 251 million years ago, 96% of life on Earth died out as a result of massive volcanic eruptions in the Emeishan and Siberian Traps. Ash clouds blocked the sun, preventing photosynthesis, and released toxic elements into the ocean.

4.) The Triassic-Jurassic Extinction, 200 million years ago, 50% of life on Earth lost. Caused by further volcanic eruptions in the mid-Pangean flood basalts.

5.) The Cretaceous-Tertiary Extinction (The Comet), 66 million years ago, 75% of life on Earth burned, obliterated or asphyxiated in the impact or the following impact winter. 

She has lived through five ice-ages. The Huronian Ice Age, Cryogenian Ice Age, Andean-Saharan Ice Age, Karoo Ice Age and the Quaternary glaciation.

She has lived through 45+ human empires (British, Roman, Russian, Mongol, Qing etc.)

She saw the creation of the Andromeda galaxy, the Triangulum galaxy, Alpha Centauri, the Milky Way, the sun, the moon.

That, my friends, is why Azrael is the way she is. She might not’ve had a loving parent, or a childhood, or freedom, or friends, or gone to camp, or to prom. She might’ve done some bad stuff, she not be as human as you’d like, but she has seen some incredible shit. So trust her, because Azrael is the best resource you will ever find and she will get you out of some tricky situations.

END-PERMIAN (250 Ma) - “The Great Dying”

Severity: 1st worst

Cause: Eruption of Siberian Traps

Climate: Cold to extremely warm; ocean acidification and anoxia, ozone destruction

Aftermath: Permanent ecosystem reorganization; low O2 for >106 years

There’s good reason why the End-Permian extinction is referred to as “The Great Dying”; 95% of all marine families, 53% of all marine families, 84% of marine genera, and 70% of known land species went extinct,

The extinction likely occurred in three stages:
1. Land extinctions over ~40,000 yrs
2. Very abrupt marine extinctions
3. Second phase of land extinctions

Calcifying marine organisms such as brachiopods and bryozoa were the hardest hit, representative of ocean acidification. The last of the Cambrian fauna also died off, and this was the only known mass extinction of insects

So what exactly made the End-Permian extinction so severe? There truly was a perfect storm to make this the deadliest million years in Earth’s history.

Earth had been emerging from a moderate ice age when the largest flood basalt event in history (the Siberian Traps) occurred, which released vast amounts of CO2. The oceans then became increasingly warm, acidic, stratified, and euxinic from decaying organic matter. The atmosphere also became flooded with light (biogenically fixed) C, possibly from seafloor methane hydrates or from coal gas released as a result of heating from the Siberian Traps. Greenhouse gases soon caused global temperatures to spike, leading to massive extinction. Global euxinia in the oceans then became a severe problem, with sulfate reducing bacteria releasing large amounts of H2S, poisoning the oceans and atmosphere and thinning the ozone layer. These systems then created a cycle of positive feedbacks:
more die-offs → more euxinia → more H2S → more die-offs.

Marine ecosystems were forever changed after the extinction. Land ecosystems didn’t recover for ~5 My, and O2 levels remained low throughout much of Triassic time.

Click HERE to see all Mass Extinction Monday posts

anonymous asked:

What do you think about the controversy regarding the origin of intraplate volcanism (i.e.: whether it is caused by deep mantle effects such as plumes or through shallow mantle effects such as the plate model, as proposed by Gillian Foulger, Don Anderson and others)

The person who runs this blog is an igneous petrologist with a particular interest in the mantle, so you’re going to get my perspective on how I think the mantle works.

First and foremost, I am a believer in plumes. It’s actually a common thing we see in any fluid heated from below - you can even do experiments in simple fluid containing tanks and they are readily generated. 


A mantle plume is a blob of low-density, usually hot material rising up from the bottom of the mantle to at least the transition zone, but most likely up until it reaches the crust. When it does that, it would carry heat and whatever the material of the lower mantle is up with it. 

The complexity comes from the fact that we’ve never sampled the mantle, nor have we ever sampled a mantle plume directly, so we can’t physically walk out in the field and find a mantle plume to map. Instead, we see possible results of these plumes at the surface; large igneous provinces like the Ontong-Java Plateau, the Columbia River Basalts, or the Siberian Traps could be the heat from these plumes arriving and melting the other rocks near the surface to generate magma.

These plumes also tend to have long tails, like you see in that image, which could allow additional hot material to flux up to the surface even after the plume head is gone. These tails could be the type of feature that feeds hotspots such as Hawaii, Iceland, and Yellowstone that continue activity for hundreds of millions of years after the plume head has moved away.

Overall I think the evidence that these things exist is strong. You can recognize distinct compositions in the rocks that do not fit well with originating in the same mantle tapped at mid-ocean ridges where the crust breaks randomly, you can recognize that huge amounts of additional heat are required to produce something like Ontong-Java, and today even seismic instruments are starting to detect hot zones beneath places like Iceland and Yellowstone which likely represent the plume conduits. 

Now that I’ve given my prejudice and logic, let’s say a few words about the late Don Anderson, who died earlier this year. 


I did my graduate work at the same institution as Don Anderson and so got to hear a good amount of discussion of his ideas. Dr. Don Anderson was a seismologist who was extremely skeptical of the Plume model for the origin of Hawaii/Large Igneous Provinces. He built the website mantleplumes.org which is a clearinghouse for discussion of the merits and demerits of the existence of plumes. 

The main alternative to explaining mantle plumes is that plates as we understand them aren’t rigid, they twist and break in funny ways that as a consequence can allow large amounts of molten rock to come up to the surface. They have presented these models in several formats, including arguments regarding how the chemistry of “plume” magmas could be generated in the upper mantle and what kinds of seismic evidence would be produced in those cases.

In general I have found those arguments unconvincing. I’m a geochemist so focusing on those - they rely on processes I believe are much better fit with the plume model. Our best temperature estimates suggest that magmas from Iceland and Hawaii are in fact generated by abnormally hot mantle and our chemical evidence argues that many of the signatures in these locations are produced by material that has been in the mantle for billions of years, which would not be very likely IMO if plumes were simply cracks in the crust that tapped the upper mantle. When we tap the upper mantle we get something like mid-ocean ridge basalts, when we tap the lower mantle we get a much greater diversity of magmatic compositions. 

On top of that, as the quality of seismic images have improved, we’ve gotten much better at distinguishing hot zones that could be plume conduits. Plumes would be small, <100 km wide, so they’re hard for seismic techniques to detect, but we’re getting there. Here’s a possible seismic image of the Yellowstone plume conduit:  


So, I think the evidence is good that there are mantle plumes that carry up hot, old material from deep in the mantle, and we’re getting better at understanding these with time.

However, although I disagreed with Dr. Anderson and colleagues, I want to take a minute to stress the important role they play. All scientists like fitting things into simple models, and so if we can come up with a plume model that explains Iceland and Hawaii, we might just call it a day. The importance of people like Dr. Anderson to me is reminding me that it’s never that simple.

We have a plume tail model that works for Iceland, Hawaii, and Yellowstone, with volcanoes that gradually get older farther away from the Hotspot, but if we go to the Western Pacific, that setup totally falls apart. The Western Pacific is filled with seamounts that have hotspot-like chemistries but where the order is lacking.

That means something fundamentally different is happening here. Our simple plume model doesn’t do a good job of explaining a lot of things that happen on Earth, even though the chemistry of these rocks fits with coming from the lower mantle. Why aren’t they organized like Hawaii? Does that mean there are multiple types of plumes?

Dr. Anderson would reply that once we start needing 4-5 different types of plumes to explain all the different features, our plume model is breaking down and in that he’s right. No simple plume model explains all the hotspot-like features we see on Earth. Even if plumes best fit the chemistry, there’s a lot of work to do to understand what really is happening. Is there some general feature that can explain both Hawaii and these features, something related to the LLSVP discovered in the lower mantle?  Why does one spot get one type of plume while another gets a different signature? These are great questions and its required of those who like the plume model that we need to explain them. That’s the reason I liked hearing Dr. Anderson speak sometimes; even though most petrologists don’t agree with his interpretations, it’s extremely important to challenge basic assumptions and models so that they really do find the best ways to explain the data we have.

People who work on the mantle are doing a tough job. We’re trying to take tiny bits that melted out of the mantle, criscrossed the entire crust, and got up to the surface, and use those dregs to figure out an entire planet. It’s very important to make sure we don’t get lost in our own assumptions and that as techniques and measurements evolve we keep stepping back and make sure that our assumptions still hold. That’s a lesson I personally picked up from Dr. Anderson and I hope it’s a good one to share. 

Know what these things are? These are framboids - from the French ‘framboise’ which means raspberry - a type of pyrite formation that occurs in certain laminated sedimentary rocks such as the Katsuyama accretionary terrane. These indicate anoxic conditions on the sea floor, and the ones depicted here indicate deadly anoxic conditions during the late Permian, coinciding with the eruption of the Siberian Traps.