UFOs & Extraterrestrial Life

There is no paradox. CO2 was never going to go away. In fact, as demonstrated by coal and oil life acted to sequester it as
fossil carbon. So life was literally cutting the branch on which it was sitting. If the CO2 got too low, then life would be suppressed
and CO2 concentrations in the atmosphere would increase resulting in the return of milder and better for life conditions.

This is exactly what you saw during the "Snowball Earth" events billions of years ago. The faint young Sun was not maintaining
the temperatures, it was CO2 (and the H2O vapour loading it induces). Too low CO2 resulted in runaway ice formation due to
the albedo feedback. Only the near equatorial belt was relatively ice free. The rest of the planet was covered with a massive
land and sea ice cover. Over time, volcanic emissions of CO2 accumulated in the atmosphere resulting in a transition to a greenhouse
event that resulted in the melting of the ice. There is direct evidence of the consequences of this since there was a surge of
chemical weathering of rocks by the high CO2 levels in the atmosphere resulting in more carbonic acid in rain water. This
chemical weathering also helped to reduce the CO2 levels.

The 30% higher solar emissions in the visible band allow us to have a non-frozen climate even with relatively low CO2 levels
of around 300 ppmv. And we have had the ice sheet cycle over the last 3.3 million years since this level of CO2 is low enough
to allow for orbital perturbations to grow land ice and lowered temperatures resulting in a sequestration of CO2 into ocean water
which leads to a cooling feedback. By the same token, human dumping of CO2 into the air at over 30 billion tons per year
(vs 600 million tons on average for volcanoes) is going to slam us with severe global warming. We are no longer in an epoch
where concentrations of CO2 in the thousands of ppmv range are conducive to life. But when the Sun was younger we
had lush conditions on the planet with such concentrations.

The story of climate and life on Earth is bound to CO2. If too much CO2 gets sequestered in the coming millions of years
then Earth can be an ice age Hell. This in spite of the solar output. The Sun is not increasing its emissions of visible band
light that fast and it will take billions of years for it to become a red giant. But plate tectonics will not stop like on Mars
since we have more than enough radioactive decay and Earth interior volume to keep mantle convection going for billions
of years. So we can have volcanism induced global warming extinctions in the future such as the ones that occurred during
the Siberian and Deccan traps.

Instead of a paradox, there is the chance event of having a planet of the right size and chemical composition in the right
orbit. Since there are so many Earth-like planets out there, this is not such a low chance. The chance of getting a
satellite moon which acts to stabilize the axis of rotation of the Earth is a substantial element. Over time the Moon
is moving away from the Earth, but this process is very slow so the impact on climate in the coming billion years from
this process is not going to be a factor.

Then there is the chance of not being exposed to a supernova in our stellar neighbourhood.