Humans and the Environment

Mass Extinction& Anthropocene

100

Define a mass extinction

When about 70+% of species disappear in a short time (2.8 million years or less)

200

What is one way in which humans have left a mark on sediment layers and geologic time?

Nuclear bombs, fly ash, plastics, disappearance of many species

300

What are some factors have caused a DROP in CO₂ levels in past mass extinctions?

Evolution of plants (moss and vascular plants each caused mass extinctions), algae blooms from nutrient runoff

400

What factors have caused a RISE in CO₂ in past mass extinctions?

Volcanic activity like Siberian basalt baths and breakup of Pangea. Release of methane deposits like those in the ocean.

500

Give one argument in favor of the recognition of the Anthropocene and one argument against

In favor- Clear evidence of changes caused by humans (plastics, nuclear isotopes, fly ash, etc..)

Against- Too little time has passed to view in the full context of geologic history.

Early Human Impacts

100

A large animal, typically over 99lbs.

Megafauna

200

Explain the Pleistocene Overkill Hypothesis

Idea that humans drove large mammals extinct through over-hunting, cause extinction of 70ish% of megafauna.

300

What may have caused an unusual spike in CO₂ 8,000 years ago and why?

Early agriculture--> land converted from forest to farmland retains less carbon. Leads to erosion of sediment.

400

What is one way in which scientists collect evidence of early human impacts on the environment?

LiDAR imaging, soil core samples/ fossilized pollen, fossilized animal remains

500

Give at least one example of a way in which early humans had a POSITIVE impact on their environment.

Aztec chinampas, terra preta, use of controlled burns to increase biodiversity.

Human population growth

100

The maximum population that of a species that an ecosystem can support at a given time

Carrying Capacity

200

Give an example of a limiting factor

Food, habitat, disease, sunlight, water, etc...

300

What has happened to the rate of growth of humans since the 1960's and why?

It was decreased by a lot. Access to birth control, women in workforce, economic cost of raising children.

400

What are the current estimates for the maximum human population that Earth can sustain?

Between 1 billion and 1 trillion. (most commonly between 2 and 16 billion)

500

What factors led to the great acceleration in human population in the 19th and 20th centuries?

Vaccination, sanitation, industrial revolution, pasteurization (removal of limiting factors)