Chapter 3: Earth’s Modern Atmosphere Study Guide
is a simple mixture of gases that is naturally odorless, colorless, tasteless, and
formless, blended so thoroughly that it behaves as if it were a single gas.
the principal substance in the modern atmosphere.
Means “outer sphere”,
Has rarefied atmosphere and is nearly a vacuum
Contains scarce lightweight hydrogen and helium atoms, is weakly bound by
gravity, and is as far as 32,000 km (20,000 mi) from Earth
When referring to the atmosphere, think of it in layers, then break it down into three
, and function
. Table 3.1
Is weight (force over a unit area) of the atmosphere on us.
The atmosphere exerts an average force of approximately 1kg/cm
at sea level.
Over half the total mass of the atmosphere is compressed below 5500 m, 75%
occurs below 10,700 m, and 90% is below 16,000 m. All but 0.1% of the
atmosphere exists below an altitude of 50 km.
The outer atmosphere in terms of composition
Begins at about 80 km altitude and extends outward to the exosphere and
interplanetary space transition
Has less than .001% of the atmosphere’s mass
The gases are not evenly mixed
Hydrogen and helium are at the margins of outer space and oxygen and nitrogen
are dominant in lower heterosphere.
Below the heterosphere, in terms of composition
Extends from an altitude of 80 km to Earth’s surface
Atmospheric density rapidly changes in the homosphere and the blend of gases is
nearly uniform throughout
The air of the homosphere is a vast reservoir of relatively inert
, a key
element of life, lies within nitrogen-fixing bacteria and is 78% of the atmosphere;
forms about one-fifth of the atmosphere and forms compounds that
compose about half of Earth’s crust and makes up 20.9% of the homosphere; the
constitutes for less than 1% of the homosphere, is unusable in life
processes, and is residue from the radioactive decay of potassium-40; carbon
dioxide is important for maintaining global temperatures at only .039% of the
atmosphere. Table 3.2**