Late Devonian Extinction
The late Devonian extinction is one of the most major extinctions in earth's history. A huge amount of animal species want extinct at that time due to a whole array of possible theories. Nineteen percent of families (life classification) went extinct at this time.
Theories
Meteorite Impact- One possible theory is that a meteorite may have hit earth, causing sediment to cloud the skies. This could prevent photosynthesis, killing plants and causing the food chain to collapse.
Plant Evolution- As plants became more prominent, it is possible that their CO2 intake changed the climate of the earth. When flourishing plants take in CO2, it reduces the amount in the atmosphere. Since CO2 is a greenhouse gas that keeps the earth warm, a lack of it may have caused extreme climate change.
Soil Erosion- With a lot of new plant life such as trees, more soil on land was loosened. With the nutrients in this soil now coming to the water, this provided an opportunity for the population of algae and other aquatic plants to grow. Similar to an algae boom, this depleted oxygen in the water, killing off a lot of aquatic life.