Slow decay of natural sources of radiation is being blamed for reduction of natural volcanism, ice ages and the lack of CO2 in atmosphere.
Volcanos are powered by the radioactive decay, and they are the major source of CO2 on the Earth. As we are, slowly, running out of radioactive materials, Earth is cooling down, volcanic activities are diminishing and so is CO2 in the atmosphere. CO2 concentration in the atmosphere is about 5x less now than in the dinosaur era.
That radiation decline, and the cooling, too, are both negative exponential functions. Which means that by now they are VERY slow declines. Unless there was a trip point of some sort of the internal Earth cooling, something else started the rather sudden and wildly cyclical period of glaciation cycles (Ice Age) we are now in (for roughly the last 40 million years.)
What the beginning of our Ice Age DOES correspond to is movement of continental plates and associated events, most prominent of which has been India crashing into Asia, forming the Himalayas (etc.), which are a giant CO2 sink. The formation of the Isthmus of Panama, changes in ocean currents, solar radiation, vulcanism, etc., also get into the act.
Now, as an aside, and sure to irritate many FReepers, volcanoes for one thing are mainly a source of cooling actors: They emit considerably more SO2 than CO2, and then (shorter term) there are particulates belched high into the atmosphere by the big violent eruptions. (Tambora, for example.) The irritating part is that if one actually goes back to their high school chemistry, checks long held estimates of volcanic emissions over past decades, looks up consumption worldwide of fossil fuels, and does a little math and chemistry, they will find that humans are actually responsible for more CO2 production than volcanoes have been, both during recent decades.
Don’t believe me? Get out a piece of notebook paper or an envelope and run the math and chemistry yourself. Even with the above caveat about SO2 vs. CO2, volcanoes ARE prodigious producers of CO2. But humans are considerably more prodigious in our population. Few people actually comprehend how many of us 7.8 billion is.
I’m not saying some added CO2 is a bad thing: There is some reason to believe we have delayed our next period of glaciation. (Uncertain, as solar radiation “should” be a bigger driver.) I’m ok with a little warmth (and more so as I get older.) Humans REALLY don’t want to go through the next period of glaciation, if it is anything like the last few. They are cold, and, dry. The last such spell very nearly killed off humans.