The Living Earth

Industrial chemicals released into the atmosphere have damaged the ozone layer in the stratosphere

The Earth’s atmosphere has changed substantiallyover our planet’s history

• The Earth’s atmosphere differs from those of the other terrestrial planets in its chemical composition, circulation pattern, and temperature profile

• The Earth’s atmosphere evolved from being mostly water vapor to being rich in carbon dioxide

• A strong greenhouse effect kept the Earth warm enough for water to remain liquid and to permit the evolution of life

The appearance of photosynthetic living organisms led to our present atmospheric composition, about four- fifths nitrogen and one-fifth oxygen

Studies of earthquakes reveal the Earth’s layeredinterior structure

Waves …

Seismologists deduce the Earth’s interior structure by studying how longitudinal P waves and transverse S waves travel through the Earth’s interior

The Earth’s Internal Structure

• The Earth’s inner and outer cores are composed of almost pure iron with some nickel mixed in

• The mantle is composed of iron-rich minerals

• Both temperature and pressure steadily increase with depth inside the Earth

The Earth’s magnetic field produces amagnetosphere that traps particles from

the solar wind

• Electric currents in the liquid outer core generate a magnetic field

• This magnetic field produces a magnetosphere that surrounds the Earth and blocks the solar wind from hitting the atmosphere

• Most of the particles of the solar wind are deflected around the Earth by the magnetosphere.

A bow-shaped shock wave, where the supersonic solar wind is abruptly slowed to subsonic speeds, marks the outer boundary of the magnetosphere

An increased flow of charged particles fromthe Sun can overload the Van Allen belts and cascade toward the Earth, producing aurorae

Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen belts

Density

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• The average density of any substance depends in part on its composition

• An object sinks in a fluid if its average density is greater than that of the fluid, but rises if its average density is less than that of the fluid

• The terrestrial (inner) planets are made of rocky materials and have dense iron cores, which gives these planets high average densities

• The Jovian (outer) planets are composed primarily of light elements such as hydrogen and helium, which gives these planets low average densities

The Terrestrial Planets

• The four inner planets are called terrestrial planets– Relatively small (with diameters of 5000 to 13,000 km)– High average densities (4000 to 5500 kg/m3)– Composed primarily of rocky materials

Jovian Planets

• The four giant outer planets are called Jovian planets– Large diameters (50,000 to 143,000 km)– Low average densities (700 to 1700 kg/m3)– Composed primarily of hydrogen and helium.

Pluto: a Dwarf planet

•Pluto is a special case

– Smaller than any of the terrestrial planets

– Intermediate average density of about 1900 kg/m3

– Density suggests it is composed of a mixture of ice and rock

The abundances of radioactive elements revealthe solar system’s age

• Each type of radioactive nucleus decays at its own characteristic rate, called its half-life, which can be measured in the laboratory

• This is the key to a technique called radioactive age dating, which is used to determine the ages of rocks

• The oldest rocks found anywhere in the solar system are meteorites, the bits of meteoroids that survive passing through the Earth’s atmosphere and land on our planet’s surface

• Radioactive age-dating of meteorites, reveals that they are all nearly the same age, about 4.56 billion years old

Radioactive Decay

• Some atoms are unstable and decay (via the weak nuclear force)

• The amount of time it takes for half of a given sample of atoms (N0 to .5 x N0) to decay is a fundamental quantity for that atom and is the atom’s half-life, t1/2

• N = N0 x e –λt

• The decay constant is λ = (ln 2) / t1/2

Some Radioactive Elements

• 14C decays to 14N, half-life 5730 years

• 60Fe decays to 60Co, half-life 1.5 x 105 years

• 40K decays to 40Ar, half-life 1.3 x 109 years

• 238U decays to 206Pb, half-life 4.5 x 109 years