80KM or 50 miles is what the height the government uses to get the space shuttles into space
A black hole.
As a river gets older sediment load decreases due to the age of the river and erosion
The grasses and other plants in a wetland act as a filter for the water, removing contaminants, cleaning up the water. The soil holding the plants acts like a sponge, sops up pollutants.
STRATOSPHERE
Several reasons. The prominent reasons are that if you go too high you'll run low on oxygen and possibly be blown off course by strong winds.
All passenger airplanes cruise at the stratosphere.
the clouds
Which mesosphere? The one for the Earth's atmosphere or for the inside? Well, I'll talk about inside. Extremely hot temperatures (since it is the middle of the Earth's inside) so about a few thousand celsius. The mesosphere in the atmosphere is very cold with temperatures as low as -90 degrees celsius.
anything to keep you warm
very warm clothing
Evidence is not used to support theory.
Theory is used to explain evidence, and to predict where and how new evidence may be found.
When new evidence is found that theory can't explain, the prevailing theory is modified or discarded.
It did, the Concorde travelled at 60,000 feet and it's cruising speed was 1,350 MPH. It went higher because of its higher cruising speed.
Bacteria function in the nitrogen cycle as nitrogen fixers and denitrifiers. Nitrogen fixing bacteria take in atrmospheric nitrogen gas and "fix" it into a nitrate or nitrite that can be used by plants. Denitrifiers decompose dead plant tissues and release nitrogen to the atmosphere.
Mesosphere
The shape, size, and mass of water molecules do not change between the solid and gas phases.
All spacecraft returning to Earth, space shuttle or otherwise, experience extreme heating as they go through the upper levels of atmosphere. The shuttle orbiters used ceramic tiles and other heat protection. Capsules such as Soyuz, Dragon and Orion use heat shields which direct heat away from the vehicle.
I have no idea