Signs and symptoms are both signals of injury, illness, disease â signals that something is not right in the body. A sign is a signal that can be seen by someone else â maybe a loved one, or a doctor, nurse, or other health care professional.
Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminum, calcium, and potassium. Oxidation of the iron dust is what gives the surface its reddish hue. Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration.
The nitrogen cycle in nature is very important. Nitrogen gas (dinitrogen, N 2) makes up about 78% of the atmosphere by volume. The atmosphere of Mars contains less than 3% nitrogen. There are relatively few minerals containing nitrogen but nitrates such as saltpetre (NaNO 3) are very important.