Week 12 Flashcards
Dating the Permian Extinction
- Zircon contains small amounts of uranium – since we know how long it takes for uranium to decompose to lead, we can determine how old the zircon crystal is
- Correlation of geologic sites containing deposition of the End-Permian in South China and East Greenland lead to the date 251.939±0.031 Myr (S.Z.Shen et al., 2019)
- The duration of extinction was short, most animals dying off in the 10-60kyr around the peak, whereas plants were lagged in their extinction from the peak by ~100kyr+
Sediments show the whole extinction likely lasted between 0.72 – 1.22 Myr
State of the Permian
- With the assembly of Pangaea, large inland deserts formed as continents were deprived of warm, tropical oceanic waters
- Low food supply
- Swamps and wetlands species disappeared
- A massive Flood Basalt eruption occurred at 251.2±0.3 Myr ago
- While hazard from flood basalt volcanoes is relatively low, many ‘explosive’ eruptions would have occurred with contaminated magmas, which could produce large quantities of volatiles
The Great Dying
- Global oceans warmed, forced to expel dissolved oxygen, leading to widely anoxic oceans
- Warming oceans release methane clathrates, which are 80x more effective at warming the atmosphere than CO2
- Great Dying theory:
- massive meteor strikes Antarctica, initiating the Siberian Traps volcanism;
- Causes Rapid global warming
- Disruption of oceanic circulation, allowing deep-water anoxia;
- Expulsion of methane into the atmosphere, prompting more severe anoxia and very high global temperatures.
The KT Boundary
- A global sedimentary layer that contains 600x more Iridium than the Earth norm
- Iridium (Ir) has widely been accepted as an indicator for extraterrestrial material
- Later, it was discovered the KT Boundary was composed of two layers:
1.The upper Fireball Layer, averaging 3mm thick and composed of carbon-rich debris – basically, everything at the surface worldwide was vapourized
2.The lower Ejecta Layer, ranging from 2mm in China up to 10m in the Caribbean, containing tektites and shocked coesite and stishovite
The Chicxulub Crater
- 1000m deep in the ocean, 180km diameter Chicxulub Crater is now the obvious trigger of the End-Cretaceous Mass Extinction, and the event forming the global, Ir-rich KT Boundary
- Some scientists mention a 500km-diameter crater striking off of India at the same time as the KT Boundary – but it remains widely unproven
- The impact of a 10km-across carbonaceous chondrite launched 5 billion Gigatons of swampy debris into the atmosphere
The Cenozoic Period
For many, food had all but disappeared, and few had the means to sustain themselves in the wasteland of the early Cenozoic
Mammals, as omnivores, were able to eat whatever they could scavenge – whether it be a dead carcass or leafy plant
Small mammals had already found many hiding places from the overwhelmingly dominant dinosaurs – for many, burrowing saved their species
Today, some scientists still argue whether the Chicxulub impact is really the trigger of the 66Ma extinction
Uniformitarianists like the Deccan Traps as the source of the extinction, but the air temperatures following the impact cannot be explained by long-duration volcanic eruptions!
Global temperature, as you know, peaked at the PETM – though a very sharp spike in global average temperature occurs right at the KT Boundary
Almost everything falls into place for the Chicxulub Crater being the extinction trigger – except the postulation of the huge 400x600km Shiva Crater off the coast of India
While little updated evidence exists to support this, the Shiva Crater impactor would have been ~40km in size!
It is postulated by the discoverers that this triggered the End-Cretaceous Extinction and the formation of the Deccan Traps, which slightly overflow onto the proposed crater
The Holocene Epoch
- Ongoing loss of species on Earth
- Estimates lose 25% of current species by 2125, and up to 66% by 2200
- Almost exclusively driven by humans and human practices, causing habitat destruction, resource over-exploitation, pollution, and climate change
- Current extinction greater than prior mass extinction – most of the Earth’s large mammals and birds will be extinct in 40ka
- Holocene Extinction is three waves:
First Wave – Spread of Modern Humans (40,000ka – 1800AD)
Second Wave – Spread of Europeans (1500AD – 1970AD)
Third Wave – Globalization (1970 – 2100)
There is a direct relation between species extinctions and increasing human population
The Spread of Modern Humans
- Extinctions were the result of overkill or over-exploitation
- Agricultural Revolution and evolution to the Stone, Iron, and Bronze Ages set major waypoints in the environmental impact of humans
The Spread of Europeans
There are 869 (and counting) species extinctions directly linked to the colonization and proliferation of European explorers and settlers/farmers
Between 1500 – 1970, the extinction rate driven by the activities of Europeans was ~70x the normal background extinction rate
~72% of extinctions due to European colonization occurred on islands, where fragile and isolated environments were highly susceptible to the effects of disease, habitat loss, over-exploitation and the introduction of invasive species
The most devastating effect the Europeans had was the diseases they carried
The ravaging effects of old European diseases on native populations are well-noted – in plants, animals and people
Globalization
Since the rapid globalization of most countries, species populations have notably declined since 1970, mostly in tropical regions where biodiversity is (or was) strong
21% Mammals, 12% Birds, 30% Amphibians are Threatened or facing extinction
Since 1970, humans have depleted ~40% of the world’s forest cover, causing reduced carbon capture by forests and habitat destruction
An estimated 15,000,000 ha of land is deforested annually
Causes for Disaster
- Loss of Habitat
- Over-Exploitation
- Invasive Species
- Climate Changes
- Pollution
- Disease
Loss of Habitat
Probably the most effective method of driving the Holocene extinction;
Over Exploitation
- Over-use of any non-renewable natural resource, or using a renewable resource at an unsustainable rate, often depletes nature of some essential pieces of the environment;
- In the 1800s, steamships in the Great Lakes used wood near the shore to burn and power their boats; when the wood quickly ran out, captains caught and dried Sturgeon to burn as logs – now there’s no more sturgeon
Invasive Species
Isolated populations, such as those on islands, are greatly affected by invasive species; introduction of new species can threaten the native food cycle and predation
Climate Change
15-37% of regionally endemic species will be extinct by 2050, upsetting and depleting food chains
