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.
On Earth, oxygen and silicon are the two most abundant elements, with silicon only found in the Earth's crust. The Earth's crust mostly consists of silicon, aluminum, iron, calcium, sodium, potassium and magnesium. All these elements are present in igneous rocks throughout the Earth.