Macroevolution and the Sixth Mass Extinction

Flashcards covering macroevolution, current extinction rates, causes of habitat alteration, greenhouse gases, and climate change data based on lecture notes.

Three major threats to biodiversity

The primary causes of biodiversity loss, ranked as: 1st: human alteration of habitats; 2nd: invasive species (mostly human-introduced); and 3rd: overharvesting.

Determining extinction

The criteria for declaring a species extinct, which requires that no individuals of that species have been seen in the wild for $50$ years.

Sixth major extinction

A current event that many scientists conclude is already underway, with extinction rates estimated to be $100-1,000 \times$ higher than the background rate.

Background extinction rate

The natural rate of extinction used as a baseline for comparison with current cumulative extinctions of mammals, birds, and other vertebrates.

Eutrophication

A process caused by too many nutrients arriving from fertilizer run-off, which creates algae blooms and leads to the formation of dead zones.

Dead zone

An oxygen-deprived area of water, such as the $5,800$ square mile region in the Gulf of Mexico, where living organisms die or avoid the area due to lack of oxygen.

Ocean acidification

The process where increased dissolved $CO_2$ makes water more acidic, leading to the destruction of coral reefs which house $1/4$ of the ocean's biodiversity.

Milankovitch cycles

Three Earth orbit cycles occurring at $96,000$, $42,000$, and $22,000$ year intervals that influence global temperatures by reinforcing or offsetting each other.

Greenhouse gases

Atmospheric gases that trap heat like glass on a global scale; according to the text, there are approximately $8$ such gases, with three being the principal (worst) contributors.

$CO_2$ (Carbon Dioxide)

A principal greenhouse gas that rose from $280 \text{ ppm}$ in 1800 to $405 \text{ ppm}$ in 2018, primarily due to burning fossil fuels and deforestation.

Methane ($CH_4$)

A greenhouse gas that is $\text{~} 21-23$ times more effective at holding heat than $CO_2$, primarily sourced from livestock and landfills.

Nitrous oxide ($N_2O$)

A greenhouse gas sourced from burning fossil fuels and the release of nitrogen fertilizers applied to agricultural crops.

Greenhouse effect

The phenomenon where light transformed to heat energy cannot pass back through the atmosphere, thereby heating the planet.

Ice cores

Glacial samples used to measure ancient $CO_2$ levels by capturing atmospheric air preserved in ice bubbles for more than $400,000$ years.

RCP 8.5

A computer projection scenario where greenhouse gas emissions continue to rise throughout the twenty-first century, potentially raising extinction rates by reducing suitable habitats.

Phenotypic plasticity

Referred to as being "plastic," this describes the ability of an organism to change its phenotype in response to environmental changes, such as climate change.