If all fossil fuels come from dead plants and animals of the past, was all the carbon trapped in them present in the atmosphere as CO2 at some point? If we dug out all the fossil fuels in the world and burned them all today, would the atmosphere be comparable to what it was like before life?
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Atmosphere was also much richer in oxygen at that time, so it would be different anyway. Also, not all carbon is bound in fossil fuels, sedimentary rocks like limestone also have carbon in their structure.
Actually, at the time, the atmosphere had less CO2 than now in it, because all that carbon was trapped in those dead plants. For one reason or another, a lot of dead plants did not decompose (whether there wasn’t a bacteria that ate them, or because they sank to the bottom of the oceans, or many other reasons).
Eventually, when the world biome and geography got to a place for those plant corpses to decompose, the CO2 level in the atmosphere went up, although some of the carbon was trapped in underground deposits that have become oil and natural gas deposits.
No, it wouldn’t be comparable to what it was like before life. If nothing else, the oxygen in Earth’s atmosphere was made by, and is maintained by, living things. In fact, life is responsible for major changes in Earth’s geology; more than half the minerals found on Earth require the oxygen in our atmosphere to form.
But to a lesser extent: yes, by burning fossil fuels we’re returning carbon that has been buried and kept out of the atmosphere for eons, and returning the Earth to a state of higher carbon dioxide in the atmosphere. Before the formation of those deposits, Earth was much hotter – there were palm trees at the poles – and in the most extreme climate change scenarios that’s basically what we go back to. (Realistically, not all fossil fuels are economical, and that shift will take a very long time. So we won’t see that in our lifetimes even in the worst cases.)
There was a time when most of the co2 in fossil fuels was in the atmosphere. This time was not the same day. It took millions of years for the build up of sequestered co2. The earth releases co2 through geological processes all the time.
What is important to remember is when there is more co2 in the atmosphere we know what happens to the climate. There is evidence of temperature rise.
We know climate change is real. Just because co2 in fossil fuels used to be in the atmosphere don’t mean it’s ok to release it again.
>was all the carbon trapped in them present in the atmosphere as CO2 at some point?
Yes, but that carbon wasn’t sequestered into plant material overnight. This took millions of years and the amount of CO2 varied with time.
The reason coal deposits in particular were even able to form was because the animals and bacteria needed to break down plant matter didn’t exist yet so piles of plant material accumulated and were buried without being decomposed.
>If we dug out all the fossil fuels in the world and burned them all today, would the atmosphere be comparable to what it was like before life?
No, the atmosphere had a very different composition back then and included Methane, Argon, and very little Oxygen.
Life itself is what changed the atmosphere.
Virtually all the Oxygen we breath comes from plants and single celled organisms like Plankton that broken down Carbon Dioxide through photosynthesis.
Overtime more CO2 was added to the atmosphere from Volcanoes and other natural processes. While more and more Oxygen entered the atmosphere.
Oxygen bonded with free Iron in the Oceans creating the banded iron deposits we mine today.
Oxygen bonded with the Methane in the atmosphere turning it into CO2 and water
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