Cyclic extinctions in the fossil record

1. Cyclic extinctions in the fossil record Alex Cook

2. Thoughts • Evolutionary progression seems to be clearly demonstrated in that certain kinds of creatures in the upper layers of the fossil record are rarely if ever seen in lower layers. Many layers also show specialized environments. Some layers contain mostly fish and invertebrate fossils while other layers show animals indicative of land. Since each of these layers seems so specialized it is easy to conclude that one type of creature gave rise to the next type of creature over the course of whatever time that it took to form the various layers between them

3. Reasons for extinction • The most common reason we see that a species go extinct is the Darwinian thought that they could not cope with their surroundings, but actually paleontologists do not know real reasons for thousands of extinction events in the fossil record whether they were large or small events.

4. Types of cyclic extinction • Raup and Sepkoski’s study of marine invertebrates over the last 600 million years found that 2 to 5 families disappeared each million years, background extinctions. • They also found that 5 intervals in that time period where 10 to 20 families became extinct, these were called “mass extinctions.”

5. The “Red Queen” theory • Species must consistently improve to avoid extinction. • They must compete for resources while natural selection is constantly changing species to keep up. • “You must keep running and running to stay in the same place.” (Alice through the looking glass)

6. Asteroid Impact • This very popular theory says that extinctions are due to large asteroids hitting the earth and causing immense climate change due to tidal waves, and blackouts associated with debris from the impact.

7. Tectonic activity • Another theory put forth by paleontologists is that volcanoes and plate tectonics could cause extinctions, this would be done by again coating the earth in ash and blowing thousands of tons of ash into the atmosphere causing a dark earth, which leads to a cold earth. This would also hurt photosynthetic activity in ocean and land plants.

8. Ice Age • Still another idea for mass extinctions is that shift in climate or another process stated earlier could trigger an ice age, cooling the planet tremendously, newer studies show that this type of climate change can occur very quickly and with out too much warning. This type of catastrophe is very real

9. My ideas • I would like to propose that the reason for many background extinctions. The environment changes due temperature, or other processes, this makes some species less suitable to live in the new surroundings and they die out. • The mass extinctions, I think are due to catastrophic events like impacts, tectonic activity, or ice ages.

10. Conclusions • Cyclic extinctions could be caused by many processes. These events are still major mysteries in today’s geology, extinctions are some of the most studied events in all of geology. With continued study and research scientists can hopefully understand these amazing events.