The thermosphere doesn't have a definitive upper or lower boundary like a solid object. It's a layer of Earth's atmosphere that blends gradually with the layers above and below. Here's how it's generally understood:

* Lower boundary: The thermosphere starts around 80-90 kilometers (50-56 miles) above Earth's surface. This is where the mesosphere ends.

* Upper boundary: The thermosphere extends to around 600-1,000 kilometers (373-621 miles) above Earth, where it transitions into the exosphere.

So, it's more accurate to say that the thermosphere ranges from 80-90 kilometers to 600-1,000 kilometers above Earth, rather than having a specific "height."