How & Why we Study
the Past
the Past
What are the 3 major types of proxies (signatures) in rocks that we use to reconstruct Earth's past conditions?
Physical, chemical, & biological
In order, name the 'Big 5' mass extinctions that came before this one.
Ordovician, Devonian, Permian, Triassic & KPg.
Bonus 500 points for any team that can tell me the years in which these events took place (within +/- 20 million years).
Although extinction 'triggers' have changed throughout Earth history (volcanos, impacts, humans, etc.), the direct causes for extinctions is always the same; that is: _____________________
Rapid Climate Change
(would also accept: rapid perturbation to the C cycle)
When extinctions occur within ecosystems, this often disrupts the entire food chain, causing cascading extinctions.
We, humans, sometimes think of ourselves as separate from this process. This is one example of a mindset called _________ ______________.
Human Exceptionalism
What are three ways we can lower atmospheric carbon concentrations?
Induced continental weathering projects
Planting trees
Regenerative agriculture
Ocean fertilization
Give one example of each major 'type' of proxy (signature in rock record).
Physical: texture, structure, etc.
Chemical: isotopes, trace metal enrichments, etc.
Biological: fossils, biomarkers, etc.
What makes the 6th mass extinction different than the past 5 mass extinctions of this Eon?
Climate change is not the only cause.
Other human activities are contributing which are changing Earth in ways it has never experienced before.
Someone says "Earth's climate has always been changing, so why are we so worried about it now?" How do you respond?
It is the rate of change that is dangerous to life on Earth. If too rapid for life to adapt to, mass extinctions occur. We've seen this every time that climate has changed as rapidly as it is today.
Over the last ~50 years, about _____ % of species on Earth (both terrestrial & marine) have shifted to higher latitudes and/or elevations due to the current rapid warming trend.
50%
What are two ways we can combat the Urban Heat Island (UHI) effect?
White roofs, more vegetation, better infrastructure (more air circulation allowed).
Stable isotopes are useful tools for studying past climate change events because they move through chemical reservoirs at different rates depending on their ______. This 'fractionation' of isotopes across chemical reservoirs allows us to use their ratios to gain insight into past periods of climate/ environmental change.
mass
(1) What was the major cause of the Late Devonian Mass Extinction event & (b) what is one thing we can learn from this event that helps us better understand and/or combat modern climate change?
(a) the spread of trees on land increased rates of weathering, photosynthesis, & soil formation (all of which take up atmospheric CO2)
(b) it teaches us how reforestation & increased weathering rates can cool global climate.
Why did the PETM (one of the most rapid global warming events in Earth's history) NOT cause a mass extinction on par with the Big 5?
Life was warm-adapted.
It's estimated that a 5°C warming at a rate of 10°C per million yrs would cause an extinction event on par w/the 'Big 5'.
What rate (per million yrs) are we currently warming Earth?
17,000 deg C / million years
One concept we have continued to highlight in climate solutions (which combats desertification, wildfires, & cascading extinctions, and increases ecosystem health & resiliency) is _________.
DIVERSITY
The Snowball Earth event during the NOE emphasizes the importance (and potential consequences of) __________ __________ mechanisms when they get out of control.
Positive feedback mechanisms
(These can cause 'tipping points' where climate starts to 'run away' & they can go either way- cooling or warming*)
Name 4 climatic and/or environmental changes that were occurring at the End Permian that are also occurring now
Warming, acidification, anoxia, desertification.
What was the series of events after the asteroid impact ~66 million yrs ago that led to the mass extinction of non-avian dinosaurs?
(1) Initially after impact, there was intense warming in and around the impact crater (due to re-entry of ejecta), (2) followed by ‘impact winter’ or rapid cooling due to the blocking of sunlight by dust & ash that was thrown up into the atmosphere, which caused major devastation among photosynthesizing life, and thus, the life that relied on these plants and primary producers, (3) and once the dust settled (literally), there was a longer-term greenhouse warming trend caused by all the CO2 emitted from impact (since the impact incinerated carbon-rich sediments), and this caused both warming-related deaths, but also acid rain, ocean acidification, & ocean anoxia.
Name 5 ways (other than burning fossil fuels) that humans are impacting the planet.
Pastics (and other pollution)
Desertification
Deforestation
Habitat destruction / Habitat fragmentation
Overuse of resources
Invasive species
Poor forest management (more intense wildfires)
Why are carbon sequestration projects better in the long-run for combating modern global warming than albedo-increasing projects?
In other words, why should we focus more on removing carbon from the atmosphere than reflecting sunlight to cool Earth?
Ultimately, we need to bring balance back to the carbon cycle.
Because this event has been caused by our removal of carbon from the geosphere, we need to put it back there to balance things out. Carbon sequestration will do this, but increasing albedo will not.
Snowball Earth began at ~716 Ma.
You are an isotope geochemist measuring stable carbon isotope ratios in ancient Precambrian limestone. What do you expect to see right before this Snowball period (~750 Ma), compared to during (~700 Ma)?
Positive C isotope excursion (spike) just before (high rates of productivity => more Corg burial)
Negative C isotope excursion (dip) during (lower biological productivity => less Corg burial)
Name 3 ways the formation of the supercontinent, Pangea, contribute to the devastation during the End-Permian Mass Extinction event?
Pangea led to (1) drying & desertification of continents, (2) stagnation of global ocean circulation which worsened anoxia, & (3) thickening of the continental lithosphere which led to the regression of shallow epicontinental seas.
We have been in an ice age for about 3 million yrs, during which climate has warmed & cooled in 'glacial cycles'. Before human activity, the warming cycles were initiated by astronomical factors, which then led to atmospheric C increase. Thus, many argue that warming causes increasing atm CO2, NOT the other way around. How does it actually work?
Increasing atm CO2 causes warming due to the greenhouse effect, AND warming causes increase in atm CO2 due to hydrate/ice melting & release of CO2 & CH4.
(1) A complication of deep ocean anoxia (a lack of O2 in the deep ocean) is that it will cause a spread of anaerobic microbes (those that don't need/like O2), most of which produce ______ which is toxic to animal life.
(2) We have actually seen evidence of this spreading in Earth's past, during the _________ _________, when oceans became so anoxic that this chemical even spread to the shallow parts of the ocean, killing many reef ecosystems!
1. H2S (hydrogen sulfide)
2. Permian Extinction (or Great Dying)
In the 6th mass extinction lecture, we talked about other ways we are impacting Earth (pollution, habitat destruction, invasive species, & overuse of resources). In terms of overusing resources, we currently use 70% of global freshwater for agriculture. What is one way we can lower this?
Reversing desertification through regenerative ag (no-till farming, planned grazing, cover cropping, polyculture, less fertilization & pesticide use) as humus-rich soils hold a lot more water.
Or switching from animal agriculture to other forms of protein like insect agriculture, which requires much less water.