65 million years ago, 60 to 80% of all life on this planet died. This is not the first time Earth has experienced mass extinctions. The fossil record shows a pattern of extinctions occurring roughly ever 26 million years. Scientists tend to agree that there have been 5 or 6 mass extinctions.

What could account for these mass extinctions? The list of suggested explanations is long, but most include

• geologic events (volcanoes)
• cosmic events (asteroids or comets)
• climatic events (hot versus cold)
• pathogenic events (diseases)

Currently the majority of evidence supports the idea that the Earth was struck by a large meteor 10-20km in diameter forming the Chicxulub Crater on the Yucatan peninsula in Mexico. Some scientists disagree and suggest that massive volcanic eruptions could have precipitated the catastrophe.

From http://education.gsfc.nasa.gov/

Think Questions

1. Is there a pattern to when the mass extinctions occur?

Image credit: https://commons.wikimedia.org

2. Could we be in a mass extinction event now?