Dino's Demise

No, I’m not talking about Dean Martin. I’m referring to the extinction of dinosaurs and what we can infer from this event about our climate, past and present. As I have previously posted in this blog, Robert Rohde of the University of California at Berkeley offers the following chart of carbon dioxide levels in our atmosphere --

http://en.wikipedia.org/wiki/Image:Phanerozoic_Carbon_Dioxide.png

I believe that this seems a thoroughly researched attempt to track carbon dioxide levels in our atmosphere over the last 600 million years. In viewing this chart (you may want to print it out to better follow the following discussion), I got to thinking about how this might correspond to the waxing and waning of the Earth’s flora and fauna. So back to Google I went and came up with the following rough biota chronology which I would like here to relate to Rohde’s chart:

4.5 billion years ago -- The Earth was thought to be formed.

3.5-3.9 billion years ago -- First primitive life forms inhabited the Earth’s seas.

450 million years ago -- First land plants appeared on Earth. These plants, through their acquired ability to carry on photosynthesis, could absorb carbon dioxide and water and produce hydrocarbons and emit oxygen. Please note that the Rohde chart has carbon dioxide volume levels at this point at about 6,000 parts per million (about 0.6%)

230 million years ago (during the Triassic period) – Dinosaurs first appeared. Please note that the Rohde chart has carbon dioxide volume levels at this point at about 1,000 parts per million (about 0.1%). This says then that, over the previous 220 million years, plants, through photosynthesis, had seemingly reduced atmospheric carbon dioxide to one-sixth the level that it was when land plants first appeared. This can begin to explain the surfeit of hydrocarbons buried in the earth in form of oil, gas, coal, etc. The chart also shows a dip in carbon dioxide levels to a nadir of around 500 parts per million (0.05%) at around 320 million years ago which suggests to me that this is when the Earth’s salad bar was most plentiful. It was also during this period that Pangaea had started to separate itself into our present continents.

150 million years ago (Jurassic period) – Many species of dinosaur had already gone extinct and many others had taken their place. There were two primary types of dinosaurs: plant-eaters (rhoetosaurus, acrocanthosaurus, brachiosaurus, etc.) which were often gigantic (often weighing more than 80 tons) slow-moving creatures … and plant-eater eaters (often fast-moving raptors). Back at about 320 million years ago a plant-eating population probably began to appear (possibly including proto dinosaurs) which reduced the flora cover and allowed carbon dioxide levels to resurge and peak at around 2,500 parts per million (0.25%) during the Jurassic period.

70 million years ago (Cretaceous period) – Dinosaurs were thought to have gone extinct during this period. Note that carbon dioxide levels started to drop precipitously at about 100 million years ago to about 700 parts per million (0.07%) which suggests that plant life was resurging and plant-eaters diminishing most likely due to raptors holding sway. And as the plant-eating dinosaurs food supply of these raptors was reduced, the raptors began to go hungry (since they were unable to munch on plants.) Many scientists believe that it took almost 10 million years for this extinction event to occur. However, a stressed population of dinosaurs might have been dealt a coup de grace with an event like a comet strike or a massive caldera explosion. With these plant-eating machines of dinosaurs gone, plants once again had an open field and continued to reduce carbon dioxide.

5 million years ago – proto man first appeared on earth. Obviously man has, over the millennia, nurtured plants with his agriculture and exploited them for shelter and fuel. But carbon dioxide levels have not fluctuated that much during man’s sway on earth … not nearly to the magnitude as before he arrived. Obviously, because of drastically reduced carbon dioxide levels, our Earth seems to have become more susceptible to periodic ice ages (probably caused by other exogenous factors). These ice ages, in turn, have caused short-term increases in carbon dioxide levels as much of the world’s flora was buried under huge glaciers. These increases in carbon dioxide levels may have been the feedback that eventually raised the Earth’s temperature and melted much of the ice. Today carbon dioxide levels hover around 370 parts per million (0.037%) after possible recent lows of 310 parts per million (0.031%) about 40 years ago.