The Mesozoic Flashcards
When and why is it notable?
251-65 Mya
- One of warmest periods in history
CO2 and Climate connection?
• Trace atmospheric gas that efficiently traps outgoing infrared radiation
• Methane, NO2, water vapour, CFC – all greenhouses gases
• Methane decomposes into CO2 within 12 years
• CO2 remains in atmosphere for around 300 years
• Time to equilibrate around planets atmosphere
• Mean modern Earth temperature is 15 ºC
• Mean temperature with no GHG would is -20 ºC
Atmospheric CO2 is thought to be controlled by:
• Silicate weathering
• Tectonics
• Organic carbon burial/oxidation
• Igneous activity
Other greenhouse gases
water vapour CO2 methane nitrous oxide sulfur hexaflouride
• GWP means x more powerful than CO2
• Sulfur hexaflouride many times more powerful than CO2 but did not exist until industrial revolution
• Luckily not much around
Water vapour most important GHG
• Could be a positive feedback of climate change
But short residence time and NA abundance
• Carbon dioxide is therefore considered to be a key Greenhouse Gas (abundant and anthropogenic)
Greenhouse effect
- Solar is mostly UV; when radiated it is mostly IR
- Greenhouse gases absorb and re-radiate IR in all directions; mostly towards earth
See graph
- Blackbody radiation for the Sahara Desert
- Satellites show the radiation given off for the particular wavelengths
- Coloured Patches between show the absorbed energy by GHGs
Radiative Forcing
- As defined by the Intergovernmental Panel on Climate Change [IPCC], radiative forcing is a measure of how the energy balance of the Earth-Atmosphere system is influenced when factors that affect climate are altered.
- The word ‘radiative’ signifies that the factors affect the balance between incoming solar radiation and outgoing infrared radiation within the Earth’s atmosphere.
- Also used as an index of the influence a factor has as a potential climate change mechanism.
- Positive forcing tends to warm the surface while negative forcing tends to cool it. Forcing values are expressed in watts per square meter (W m-2).
Need to calculate nett forcing to determine is something causes net warming or net cooling
Are CO2 and climate closely linked?
- A large and growing body of evidence indicates that CO2 and climate co-vary; however, there is some indication that the two may not be closely linked at all times….
- Veizer et al. 2000: “Our data conflict with a
temperature reconstruction using an energy balance model that is
forced by reconstructed atmospheric carbon dioxide concentrations.”
“The results can be reconciled if atmospheric carbon dioxide concentrations were not the principal driver of climate variability on geological timescales for at least one-third of the Phanerozoic eon”
“or if the reconstructed carbon dioxide concentrations are not reliable”
Climate leading up to Triassic?
- PCO2 quite low during Carboniferous and Permian
- Increases dramatically at Permian/Triassic boundary
- The interior of Pangea was hot and dry during the Triassic
- Warm temperate climates extended to the Poles
- This may have been one of the hottest times in Earth history
- Rapid global warming at the very end of the Permian may have created a super “Hot House” world that may have contributed to the great Permo-Triassic extinction.
- Uplift in the centre of Pangaea
Triassic
251 to 199 ma BP
• All land assembled together as Pangaea
• Marine and terrestrial adaptive radiation
• Taking advantage of ecological niches left after P/T extinction killed off much of world’s life
• Reptiles expand dramatically
• Evolution of first flowering plants (angiosperms)
• All models, geological, and biological evidence suggest Greenhouse conditions
• No glaciation
Triassic ‘Coal Gap’
Global “Coal Gap” or “Coal Crisis” – no coal found anywhere for approximately 7 million years (250 ma BP to 243 ma BP)
• Extinction of peat forming plants?
• Evolutionary advances in the effectiveness of fungal decomposers, insects, or tetrapod herbivores?
• Changes in sea level?
Jurassic
(199 to 145 ma BP)
• Age of Dinosaurs
• Marine vertebrates consist of marine reptiles and fish
• The invertebrate rudist corals and belemnites appeared
• Late Jurassic birds first appear evolving from coelurosaur dinosaurs
Early Jurassic
• Pangaean ‘Super-monsoon’ controlled climate during the Early and Middle Jurassic
• Due to massive continent
• Rising warm air from continent pulls in moist air from sea
• The interior of Pangaea still very arid and hot
• A climate of extremes
• Deserts covered what is now the Amazon and Congo rainforests
• China, surrounded by moisture bearing winds was lush and verdant
Intercontinental sea will start opening up
Late Jurassic
- The global climate during the Late Jurassic changing gradually due to breakup of Pangaea
- The interior of Pangaea became less dry, and seasonal snow and ice frosted the polar regions
- Still no real glaciers
Cretaceous (Early)
(145 to 65 ma BP)
Early Cretaceous
• Pangaea is breaking apart, by late Cretaceous completely
• The Early Cretaceous was a mild, almost ‘cool’ world
• Snow and ice existed during the winter seasons
• Some ‘Alpine’ glaciers in higher latitudes, higher altitudes
• ‘Cool Temperate’ forests covered the polar regions
Pangaean continent broken into several smaller continents.
• High sea level flooded MOST continental interiors
• India on collision course with SE Asia.
Abundant CO2 underground
- Carbon from soils is transported underground
- Oxidised to from CO2
- Concentration in bedrock ~100% atmospheric values
o In void spaces of rock, organic material enters rock through water and breaks down - Sea level rise should force the CO2 into the atmosphere
- Rapid positive feedback
Late Cretaceous
• During the Late Cretaceous the global climate was still much warmer than today’s climate.
• No ice existed at the Poles.
• Still strong seasonality existed
Paleobotanical Evidence for Warm Climate
• Warm-adapted evergreen vegetation found north of the Arctic circle.
• Breadfruit tree leaves found north of Arctic Circle.
• Modern breadfruit trees found only warm low latitudes.
• Equator-to-pole temperature gradient different in Cretaceous.
