This question dose not have enough info to answer, i'll gladly help if this question had a date in which mercury was used or what had mercury in it.
I apologize.
Answer;
It is the last layer of the atmosphere before space.
Explanation;
-Earth's atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The exosphere gradually fades away into the realm of interplanetary space.
-The exosphere is the highest layer of the atmosphere. It extends up to 10,000 km (6,200 miles; 33,000,000 ft.) above the Earth. Satellites orbit the Earth in the exosphere. The atmosphere in this layer is extremely thin and atoms and molecules of air are constantly escaping into outer space. Free-moving particles move in and out of the solar wind in the exosphere.
