Hi Kristin. If the oven were above 120°F then it would be damaging the yeast, but since it's bubbling at all, that means it's alive and fine. All starters are different so there's nothing to be concerned about. You can move it into a glass container if you'd prefer. Removing the lid shouldn't make too much of a difference though it would release a bit of the moisture and heat so best to keep it closed if you can. We recommend using our complete Sourdough Guide rather than this blog article since it's very recently updated. 

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