Earth and Moon: Atmosphere, Tides, and Plate Tectonics

Earth's water coverage

One hemisphere of Earth is almost entirely covered with water.

Percentage of sunlight reflected

37% of the sunlight that falls on Earth is reflected into space.

Percentage of sunlight absorbed

63% of the sunlight that falls on Earth is absorbed by Earth rather than reflected into space.

Most abundant gas in atmosphere

Nitrogen is the most abundant gas in Earth's atmosphere.

Nitrogen to oxygen ratio

The ratio of nitrogen to oxygen in Earth's atmosphere is 4 parts nitrogen to 1 part oxygen.

Current atmosphere stage

The atmosphere that we are now breathing is the third atmosphere Earth has had.

Dominant gases in earliest atmosphere

The dominant gases in Earth's earliest atmosphere after it first formed were hydrogen and helium.

Reason for early atmosphere loss

Earth's earliest atmosphere, composed primarily of hydrogen and helium, did not last long because hydrogen and helium are light gases, and they soon escaped into space.

Dominant gases in second atmosphere

The dominant gases in Earth's second atmosphere were carbon dioxide and nitrogen.

Density comparison of second atmosphere

Earth's second atmosphere was roughly 100 times denser compared with today's atmosphere.

Fate of carbon dioxide

Much of the carbon dioxide from billions of years ago dissolved into Earth's oceans.

Carbon dioxide end location

The majority of the large amount of carbon dioxide (CO2) from the second major atmosphere ended up dissolved in the oceans and, via the shells of living creatures, in the limestone of many mountain ranges.

Source of oxygen in atmosphere

The presence of oxygen in Earth's atmosphere is thought to result directly from the biological activity of plants and animals.

Cause of free oxygen

The large amount of free oxygen in Earth's present atmosphere is primarily a result of biological processes such as photosynthesis.

Ozone function

Ozone in the stratosphere absorbs much of the dangerous solar ultraviolet light.

Ozone hole definition

An 'ozone hole' is a region of the stratosphere above the South Pole where ozone levels occasionally drop to very low levels.

Current status of ozone layer

The ozone layer has been somewhat depleted, but if left alone, it could restore itself in a century.

Ozone composition

Ozone is a gas consisting of molecules containing three oxygen atoms.

Stratosphere temperature reason

Earth's stratosphere is warmer than the layers above and below it because ozone in the stratosphere absorbs specific wavelengths of ultraviolet radiation from the Sun.

Stratosphere temperature increase reason

The stratosphere is heated by solar ultraviolet radiation absorbed by the ozone layer.

Maximum gas temperature altitude

The gas temperature in the stratosphere of Earth's atmosphere reaches a maximum at about 50 km due to the absorption of solar ultraviolet radiation by ozone (O3).

Importance of ozone layer

The most important reason for Earth's need of the ozone layer is that it shields Earth from harmful solar ultraviolet radiation.

UV radiation absorber

The chemical constituent that absorbs UV radiation in the stratosphere of Earth's atmosphere is O3, ozone.

Major layers of atmosphere

The major layers of Earth's atmosphere in the correct order from the surface upward are troposphere, stratosphere, mesosphere, thermosphere.

Basic structure of atmosphere

The basic structure of Earth's atmosphere consists of four layers of alternating temperature profiles: temperature decreasing, then increasing, then decreasing, then increasing with altitude.

Temperature variation with height

The temperature of Earth's atmosphere varies with height over the range 0-80 km by decreasing, then increasing, then decreasing again, with a steady rise until it reaches a high and constant value above 80 km.

Lowest temperature

The lowest temperature in Earth's atmosphere is about 200 K.

Altitude of lowest temperature

The lowest temperature in Earth's atmosphere occurs at an altitude of about 80 km.

Coldest layer location

The coldest layer of Earth's atmosphere is located between the mesosphere and thermosphere.

Outermost atmospheric layer

Earth's thermosphere is the outermost atmospheric layer in which ultraviolet light from the Sun ionizes atoms.

Hottest part of atmosphere

The hottest part of Earth's atmosphere is the upper thermosphere.

Troposphere definition

The troposphere of Earth is the atmospheric layer closest to the ground.

Coldest layer of Earth's atmosphere

Located between mesosphere and thermosphere.

Thermosphere

The outermost atmospheric layer in which ultraviolet light from the Sun ionizes atoms.

Hottest part of Earth's atmosphere

The upper thermosphere.

Troposphere

The atmospheric layer closest to the ground.

Pressure

Force divided by the area over which the force acts.

Fraction of total mass of Earth's atmosphere in the troposphere

75%.

Atmospheric pressure and altitude relationship

The pressure decreases by a fixed fraction each interval of altitude (down by ½ every 5.5 km on Earth).

CO2 concentration change over the past thousand years

The CO2 concentration was relatively constant for about 800 years but has increased significantly since AD 1800.

Change in Earth's surface temperature since AD 1000

5°C.

First person to postulate continental drift

Alfred Wegener.

Fact that gave Alfred Wegener the idea of continental drift

The shapes of the east coasts of North and South America fit nicely against those of the west coasts of Europe and Africa.

Formation of the Mid-Atlantic Ridge

Molten rock pushed up from Earth's interior and forced two crustal plates apart.

Mid-Atlantic Ridge

A region in Earth's crust where two tectonic plates are slowly spreading apart.

Number of major tectonic plates

About a dozen.

Typical speed of continental drift

A few centimeters per year.

Importance of upper mantle being 'plastic'

The continents are able to float and drift on these layers.

Evidence of Europe and North America moving apart

The existence of the mid-Atlantic Ridge.

Rate of separation between African and South American continents

About 3 cm per year.

Time since African and South American continents were in contact

170 million years.

Cause of great mountain ranges on Earth

Two tectonic plates that are moving at different velocities across the face of Earth collide.

Formation of great mountain ranges

Produced by collisions between tectonic plates.

Pangaea

Supercontinent on a tectonic plate that split into the present North and South America, Europe, and Africa.

Deep oceanic trenches

Locations where cool surface material on Earth sinks below other material at a tectonic plate boundary.

Earthquake occurrence

All the boundaries of the major interacting tectonic plates on Earth's surface are coincident with the positions of maximum earthquake occurrence.

Majority of earthquakes on Earth

Occur along the boundaries of major tectonic plates.

Subduction

The process by which cool surface material on Earth sinks below other material at a tectonic plate boundary.

Earthquake locations

Most of Earth's earthquakes occur where crustal plates are colliding, separating, or sliding past one another.

Cause of plate motions

Convective flow of material in Earth's interior.

Continental drift

Now thought to be caused by circulation currents in the deep interior, causing slabs of Earth's crust to move slowly.

Planetary differentiation

Sinking of heavier elements toward the center of a planet and the floating of lighter elements toward the surface.

Location of Earth's mantle

Between the core and the crust.

Average density of Earth

Approximately five times that of water.

Basic structure of Earth's interior

Solid iron inner core, molten iron outer core, rocky mantle, lighter rocky crust.

Seismic waves

The waves that geologists and geophysicists use to probe the inside of Earth.

Earth's solid inner core

Results from the fact that the melting temperature of an iron-nickel mixture increases with increasing pressure and rises above the actual temperature in the inner core.

Mantle and crust relationship

New crust is formed by magma rising from the mantle in some places, and old crust is pushed back down into the mantle in other places.

Earth's magnetic field

Is related to its rotation around its axis and is most probably generated by electric currents in Earth's electricity-conducting molten core.

Solar wind protection

Earth's magnetic field protects Earth and its inhabitants from the solar wind, which would otherwise irradiate and damage life forms if not deflected.

Moon's maria

The names we use for the Moon's maria were invented a few hundred years ago after the first telescopic observations of the Moon.

Maria on the Moon

Appear to be craters filled with basalt from within the Moon.

Craters on Earth

Are not apparent on Earth at the present time in the abundance seen on the Moon because plate tectonics has returned cratered surface layers into Earth's interior, and weathering has obliterated the more recent craters.

Greatest role in shaping the Moon's surface

Impacts of interplanetary bodies of all sizes.

Larger craters on the Moon

Have central peaks because the crater floor rebounded upward after the initial compression from the impact of an interplanetary rock.

Significance of central peaks

A central peak is characteristic of an impact crater formed by a shock wave.

Common shapes of lunar craters

Round because the incoming projectile vaporized and exploded to form the crater.

Mare on the Moon

Large area of darker material on the lunar surface.

Maria

Ancient lava floodplains.

Near and far sides of the Moon

The near side has several large maria, whereas the far side has only one small mare.

Appearance of the Moon's surface

Maria only on the near side, no major maria on the far side.

Major maria on the Moon

Exist only on the Earth-facing side.

Smooth, dark maria

Are immense impact basins that are smooth because they were covered by lava flows after the early, heavy bombardment had ended.

Lunar rille

Long, winding crack in the surface of a mare.

Rille

A shallow winding valley on the Moon.

Mountains on the Moon

Were mostly caused by impacts from interplanetary bodies from outer space.

Lunar regolith

Layer of fine powder covering the lunar surface.

Creation of lunar regolith

Cracking and pulverizing by meteoric bombardment.

Barycenter

Center of mass of the Earth-Moon system.

Significance of barycenter

The barycenter is the common center of the orbital motions of Earth and the Moon due to their mutual gravitational attraction.

Tidal disturbances

The Moon produces tidal disturbances on the oceans of Earth, resulting in two high and two low tides per day.

Highest tides on Earth

Occur at full or new Moon.

Tidal bulges caused by the Moon

There are two, one facing (almost) directly toward the Moon and one facing (almost) directly away from the Moon.

Spring tides

High tides that are significantly higher than the average high tide.

Neap tides

High tides that are significantly lower than the average high tide.

Occurrence of spring tides

Twice a month, at full and new Moon.

When spring tides occur

Whenever the Earth, the Moon, and the Sun form a straight line, regardless of which side of Earth the Moon is on.

When neap tides occur

Whenever the Earth-Moon line makes a 90° angle to the Earth-Sun line.

High tide on the far side of Earth

Experiences a high tide because the combination of Earth's motion and the Moon's gravity makes water move away from the Moon toward the far side of Earth.

Moon's rotation alignment

The reason for the alignment of the Moon with one face always toward Earth is that tides due to gravitational forces from Earth, while the Moon was molten, slowed the Moon's rotation.