mollwollfumble said:
PermeateFree said:
Ordovician-Silurian extinction
The first of the big five extinction events took place around 540 million years ago was the second biggest extinction event of marine life. There was only life in the seas at this time and more than one hundred families of marine invertebrates died.
Late Devonian extinction
About 375 million years ago, major environmental changes caused a drawn-out extinction event that wiped out 70% of marine species
Permian-Triassic extinction (the Great Dying)
The largest extinction event and the one that affected the Earth’s ecology most profoundly took place 251 million years ago. As much as 90-95% went extinct, and it took about 50 million years for life on land to fully recover its biodiversity – with the rise of many species of dinosaurs.
Triassic-Jurassic extinction
Dinosaurs first appeared in the Early Triassic, but large amphibians and mammal-like reptiles were the dominant land animals. The rapid mass extinction that occurred 205 million wiped out about 20% of all marine families, many reptiles and the last of the large amphibians – opening up niches for the dinosaurs of the Jurassic.
The Cretaceous-Tertiary (KT) extinction
Many researchers believe that an asteroid slammed down on Earth 65-66 million years ago at Chicxulub, Mexico. The impact is often blamed for ending the reign of the dinosaurs. It took 10 million years for biodiversity to recover from this mass extinction.
Each of those five has an associated flood basalt event.
In order to have a mass extinction, something pretty dramatic has to happen. There have been geological events that are startlingly big, but had no significant extinction associated with them. Let me take a few examples that could have created a mass extinction, but didn’t.
1. Sea floor spreading creates rift valleys. Eruptions occur that are big enough to generate thousands cubic kilometers of lava, sulfur dioxide and carbon dioxide. These occur very frequently, with little in the way of effect on wildlife. I suspect because of the absorption of the CO2 and SO2 by the seawater above them. The last really big one created Iceland.
2. Pacific seafloor resurfacing. The Pacific ocean floor contains thousands of subsea volcanic mounds. These went off virtually all at once, and not too long ago. This was a unique massive event in the history of the Earth. But no significant extinction is recorded.
3. More often than every million years, a minor flood basalt occurs above the sea surface somewhere in the world over a hotspot. For example the flood basalt north of Melbourne.
4. Ice ages. Just 21,000 years ago, an ice sheet covered Montreal to a depth of 3.3 kilometres. Talk about climate change! But no associated mass extinction.
There was an extinction event associated with human beings. But that’s over now. Even pesticides – the biggest manmade threat to life on the planet – are under control now, sort of.
My criteria for whether there is a mass extinction is “is the air breathable?” The pumping of oxygen into the atmosphere by blue-green algae was one time when the atmosphere became unbreathable. Oxygen is deadly poison to most species alive at the time.
The heating of air to extreme temperatures, above 50 degrees C over the whole of the Earth including both poles would be another way to make air unbreathable.
Dispersing SO2 into the atmosphere in such quantities as to be above LD-50 for most species (including fish), say a sustained 100 ppm. Is an easy way to make air unbreathable.
Freezing the entire water surface right down to the equator is another way to make the air unbreathable.
Then there are slow ways to create a mass extinction. Coral growth is one. Coral and mollusc growth locks away carbon dioxide as limestone, taking carbon out of the hydroshere/atmosphere/biosphere until there is none left for life. Ditto, but to a lesser extent, grass growth. Peat bogs created by grass growth in wet environments (too wet for fungi to thrive) remove carbon from the biosphere, slowly strangling it.
Moll I hate to tell you, but your opinion means absolutely nothing when compared to the research and study of thousands of experts over many decades who all agree about the five major extinction events. Sure there have also been many much smaller events, but that is not what this thread is about.
>>Each of those five has an associated flood basalt event.<<
That is simply not true in some cases and far more complicated than you infer in the others:
Ordovician-Silurian extinction
Massive glaciation locked up huge amounts of water in an ice cap that covered parts of a large south polar landmass. The icy onslaught may have been triggered by the rise of North America’s Appalachian Mountains. The large-scale weathering of these freshly uplifted rocks sucked carbon dioxide out of the atmosphere and drastically cooled the planet.
Late Devonian extinction
It’s been hard to nail down the cause for the late Devonian extinction pulses, but volcanism is a possible trigger: Within a couple million years of the Kellwasser event, a large igneous province called the Viluy Traps erupted 240,000 cubic miles of lava in what is now Siberia. The eruption would have spewed greenhouse gases and sulfur dioxide, which can cause acid rain. Asteroids may also have contributed. Sweden’s 32-mile-wide Siljan crater, one of Earth’s biggest surviving impact craters, formed about 377 million years ago.
Permian-Triassic extinction
The extinction’s single biggest cause is the Siberian Traps, an immense volcanic complex that erupted more than 720,000 cubic miles of lava across what is now Siberia. The eruption triggered the release of at least 14.5 trillion tons of carbon, more than 2.5 times what’d be unleashed if every last ounce of fossil fuel on Earth were dug up and burned. Adding insult to injury, magma from the Siberian Traps infiltrated coal basins on its way toward the surface, probably releasing even more greenhouse gases such as methane.
Triassic-Jurassic extinction
At the end of the Triassic, Earth warmed an average of between 5 and 11 degrees Fahrenheit, driven by a quadrupling of atmospheric CO2 levels. This was probably triggered by huge amounts of greenhouse gases from the Central Atlantic Magmatic Province, a large igneous province in central Pangaea, the supercontinent at the time. Remnants of those ancient lava flows are now split across eastern South America, eastern North America, and West Africa. The Central Atlantic Magmatic Province was enormous. Its lava volume could cover the continental U.S. in a quarter-mile of rock.
Cretaceous-Paleogene extinction
One day about 66 million years ago, an asteroid roughly 7.5 miles across slammed into the waters off of what is now Mexico’s Yucatán Peninsula at 45,000 miles an hour. The massive impact—which left a crater more than 120 miles wide—flung huge volumes of dust, debris, and sulfur into the atmosphere, bringing on severe global cooling. Wildfires ignited any land within 900 miles of the impact, and a huge tsunami rippled outward from the impact. Overnight, the ecosystems that supported nonavian dinosaurs began to collapse. (Learn more about the last day of the dinosaurs’ reign.)
Global warming fueled by volcanic eruptions at the Deccan Flats in India may have aggravated the event. Some scientists even argue that some of the Deccan Flats eruptions could have been triggered by the impact.
Extinction today
Climate change presents a long-term threat. Humans’ burning of fossil fuels has let us chemically imitate large igneous provinces, through the injection of billions of tons of carbon dioxide and other gases into Earth’s atmosphere each year. By total volume, these past volcanoes emitted far more than humans do today; the Siberian Traps released more than 1,400 times the CO2 than humans did in 2018 from burning fossil fuels for energy. However, humans are emitting greenhouse gases as fast as—or even faster than—the Siberian Traps, and Earth’s climate is rapidly changing as a result.
As mass extinctions show us, sudden climate change can be profoundly disruptive. And while we haven’t yet crossed the 75-percent threshold of a mass extinction, that doesn’t mean things are fine. Well before hitting that grim marker, the damage would throw the ecosystems we call home into chaos, jeopardizing species around the world—including us.
https://www.nationalgeographic.com/science/prehistoric-world/mass-extinction/
As a last comment:
>>4. Ice ages. Just 21,000 years ago, an ice sheet covered Montreal to a depth of 3.3 kilometres. Talk about climate change! But no associated mass extinction.<<
21,000 years ago was at the height of the last Ice Age when conditions were most extreme. The world has WARMED from that period until it reached our CURRENT CLIMATE. Global Warming is heating the planet ABOVE this current level to reach an environment we and most other life are not evolved to live, nor due to the rapid change, the biota of today will not be able adapt to this sudden climate change.