GTS and Mass Extinction

What would the GTS look like if it only lasted 1 hour? GTS – Timeline that organizes events in Earth’s history. Which time period would take up the most time? At what time would the appearance of mammals occur?

What is an extinction? The process through which a species disappears from Earth. Why do extinctions occur? –They often follow a sudden, drastic change in the environment. Populations of organisms cannot adapt to the changing conditions and they die

Natural causes of extinction Extinction is a natural part of evolution Scientists estimate that 99.9% of all species that have ever lived on Earth have become extinct –Examples: Increase or decrease in temperature Increase or decrease in rainfall VolcanoesEarthquake Flooding or drought Shift in in land or sea Change in food supply New predator or disease

Mass extinctions Occurs when large number of species die out in a fairly short period of time More than 50% of all species living at the time died out. –Example Mass extinctions of the dinosaurs at the end of the Cretaceous period Causes of mass extinctions –Asteroid theory: asteroids hitting Earth –Gradual theory: plate tectonics and volcanoes

What’s good about a mass extinction? New organisms can thrive –Example The mammals thrived after the dinosaurs were killed off

Humans and extinctions Humans are increasing the rate of extinctions How? –Habitat destruction –Pollution –Overfishing –Global warming –Invasive species –Over logging, overgrazing, over burning