For anybody that remembers the old blog, you may remember that I had gone down the path of geologic extinctions. In the Phanerozoic (last 542 million years) there have been 5 great extinctions and many minor extinctions. We use the Phanerozoic because that is the period that we have fossil records for.
- 450 million years ago (mya) 85% of the marine life went south.
- 374 mya 70-80% of the marine species became extinct.
- 251 mya was the greatest mass extinction in earths history where 90% of all species and up to 99% of all animals are thought to have disappeared.
- 200 mya most of the ammonites, half the genera of bivalves, many brachiopods and gastropods, 20% of foraminifera families, 80% of quadrupeds, and all conodonts became extinct. Since conodonts are extinct you probably aren’t familiar with them. They were the earliest vertebrate (backbone) animal having survived for 250 my until BANG — gone. The looked a bit like eels.
- Of course, 65 mya the dinosaurs and 2/3 of all other species with a cumulative loss of about 80% of all life on earth bit the big one with a comet or asteroid taking the blame in current thinking.
Lots of ideas on what happened to cause these extinctions.
- massive volcanism (eruption of flood basalts) and consequent alteration in atmosphere/ocean chemistry
- impact of meteorites
- variations in sea level
- significant glaciation
- release of methane or carbon dioxide due to melting of gas hydrates
- changes in the large scale circulation of ocean water as the shape/continuity of ocean basins change due to plate motion
- radiation from a nearby supernova
Keep in mind that while these extinctions happened relatively rapidly, relatively rapidly in geologic time is measured in 10’s of millions of years. Homo-Sapiens (us) have only been on earth about 200,000 years. So man may have appeared and may disappear in a period of time less than a great extinction took to complete.
