Here's a breakdown of what could be expected:
It would be silent. Sound requires a medium to transmit waves. You could feel vibrations from the ground, but you wouldn't hear anything.
Birds and planes would fall from the sky. Although we can't see air (except clouds), it has mass that supports flying objects.
The sky would turn black. It's blue because of the atmosphere. You know those pictures taken from the Moon? The Earth's sky would look like that.
All unprotected plant and animal life on the Earth's surface would die. We can't survive long in a vacuum, which is what we'd have if the atmosphere suddenly vanished. It would be much like being "spaced' or shot out of an airlock, except the initial temperature would be higher. Eardrums would pop. Saliva would boil. But you wouldn't die instantly. If you held your breath, your lungs would pop, which would be the quickest (albeit most painful) death. If you exhaled, you'd pass out in about 15 seconds and die in around three minutes. Even if you were handed an oxygen mask, you wouldn't be able to breathe. This is because your diaphragm uses the pressure difference between the air inside your lungs and outside your body to inhale.
Let's say you have a pressure suit and air. You'd live, but you'd get a massive sunburn on exposed skin because the Earth's atmosphere is what filters solar radiation. It's hard to say how much trouble you'd be in from this effect on the dark side of the planet, but being in direct sunlight would be severe.
The rivers, lakes, and oceans would boil. Boiling occurs whenever vapor pressure of a liquid exceeds external pressure. In a vacuum, water readily boils, even if the temperature is warm. You can test this yourself.
Although water would boil, the water vapor would not fully replenish the atmospheric pressure. An equilibrium point would be reached where there would be enough water vapor to prevent the oceans from boiling off. The remaining water would freeze.
Eventually (long after surface life had died), solar radiation would break atmospheric water into oxygen, which would react with carbon on the Earth to form carbon dioxide. The air would still be too thin to breathe.
The lack of atmosphere would chill the Earth's surface. We're not talking absolute zero cold, but the temperature would drop below freezing. Water vapor from the oceans would act as a greenhouse gas, raising the temperature. Unfortunately, the increased temperature would allow more water to transition from the sea into the air, likely leading to a runaway greenhouse effect and making the planet more like Venus than Mars.
Organisms that need air to breathe would die. Plants and land animals would die. Fish would die. Most aquatic organisms would die. However, some bacteria could survive, so losing the atmosphere wouldn't kill all life on Earth. Chemosynthetic bacteria wouldn't even notice the loss of atmosphere.
Volcanoes and geothermal vents would continue to pump out carbon dioxide and other gases to add to the water. The most significant difference between the original and new atmosphere would be the much lower abundance of nitrogen. Earth could replenish some nitrogen from meteor strikes, but most of it would be lost forever.
Explanation:
