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.
Oxygen gas (dioxygen, O 2) makes up 21% of the atmosphere by volume. It is the most abundant element in the earth's crust (followed by silicon). It is present in any number of minerals and makes up most of the weight of water. Oxygen is the third most abundant element found in the sun, and is involved in the carbon-nitrogen cycle, one of the processes responsible for stellar energy production. The atmosphere of Mars contains about 0.15% oxygen.