<p><span style="font-size: 16px;">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.</span></p> <p><span style="font-size: 16px;">What could account for these mass extinctions? The list of suggested explanations is long, but most include </span></p> <ul> <li><span style="font-size: 16px;">geologic events (volcanoes)</span></li> <li><span style="font-size: 16px;">cosmic events (asteroids or comets)</span></li> <li><span style="font-size: 16px;">climatic events (hot versus cold)</span></li> <li><span style="font-size: 16px;">pathogenic events (diseases)</span></li> </ul> <p><br /><span style="font-size: 16px;">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.</span></p> <p><span style="font-size: 16px;">From http://education.gsfc.nasa.gov/</span></p> <p> </p> <p><span style="font-size: 16px;"><strong>Think Questions</strong></span></p> <p><span style="font-size: 16px;">1. Is there a pattern to when the mass extinctions occur?<br /><br /><br /></span></p> <p style="line-height: 1.4;"><img src="Phanerozoic_Biodiversity_5733922a7e12a.png" alt="" id="tme_imgModEnabled" title="" /></p> <p style="text-align: center;"><em><span style="font-size: 16px; line-height: 1.4;">Image credit: </span><span style="font-size: 16px; line-height: 1.4;">https://commons.wikimedia.org</span></em></p> <p> </p> <p><span style="font-size: 16px; line-height: 1.4;">2. </span><span style="font-size: 16px; line-height: 1.4;">Could we be in a mass extinction </span><a style="font-size: 16px; line-height: 1.4;" href="http://www.mysterium.com/extinction.html">event now</a><span style="font-size: 16px; line-height: 1.4;">?</span></p> <p> </p> <p> </p>