Earth

The Earth is currently the location of all living humans in the known universe.

As Homo sapiens evolved to survive and reproduce on the Earth, around sea level, it is the most suitable environment for the physiological success of this species.

Many pathological processes occur when the human body is exposed to a significantly different environment. An understanding of the physical and chemical characteristics of Earth, is therefore fundemental to understanding environmental medicine and space medicine.

January 4, 2012. Image Credit: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

Atmosphere

• Surface pressure (at mean sea level): 101.325 kPa = 1.0133 Bar = 760 Torr
• Surface temperature: 184k to 330k (mean 288k) = -89.15 to 56.85 celsius (mean 14.85 Celsius)
• Composition by volume: 
• 78.08% nitrogen (N2)
• 20.95% oxygen (O2)
• 0.934% argon (Ar)
• 0.0408% carbon dioxide (CO2)
• ~ 1% water vapor (variable)

Partial pressure of O2 gas in the atmosphere at sea level = proportion of oxygen in atmosphere x atmospheric pressure = 0.21 x 760 = 160 Torr.

 

Planetary Structure

• Core type: metallic, iron
• Inner core: solid
• Outer core: liquid, active 
• Chemical composition:
• Iron (32.1%)
• Oxygen (30.1%)
• Silicon (15.1%)
• Magnesium (13.9%)
• Sulfur (2.9%)
• Nickel (1.8%)
• Calcium (1.5%)
• Aluminium (1.4%)
• 1.2% other elements

Global

• Mean radius: 6371.0 km
• Mass: 5.97 x 10^24 kg
• Surface gravity: 9.807 m/s^2 = 1 g
• Orbital period: 365.256 days = 1 year
• Sidereal rotation period: 0.997 days = 23h 56m 4.100s