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You're right though, I cannot speak definitively on the subject
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It's a tough one for a layperson. On the one hand big claims require big proof. On the other hand, they've been making these claims for a while and the case seems to be getting stronger. But then, I read about death threats to scientists on the 'no' side, and I wonder if it's all a religon in disguise. The usual rules of thumb for evaluating scientific evidence as a layperson don't apply here because of the politics involved.
However, I recall from geology class a non-controversial case in the past where lowly life forms completely
changed our planet:
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So life began about 3.5 billion years ago. Eventually more sophisticated organisms developed in an Earth without oxygen in its atmosphere, an atmosphere rich in carbon dioxide and unbreathable, indeed poisonous, to humans. The oxygen in the atmosphere has been mostly biologically generated: For example, countless cyanobacteria breathed in CO2 and exhaled O2 for hundreds of millions of years. Plants, when they settled on the continents, did the same. As a result, the CO2 in the atmosphere has decreased while the O2 has steadily gone up.
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