Earth

Facts Third planet from the sun, in between

Venus and Mars

Surface is covered 71% in water

Geologically active and dynamic world – volcanoes, earthquakes, erosion, etc.

Only planet that houses life

Atmosphere

Composition Air is predominantly a 4:1 ratio of nitrogen to

oxygen

These two gases are only found in small amounts on other planets

Models of early Earth history indicate that this is the third atmosphere to envelop Earth

Earlier atmospheres had no oxygen—only remnants of hydrogen and helium leftover from the formation of the solar system, which eventually escaped via thermal energy

Second atmosphere Gases that composed the 2nd one rose from volcanoes and

cracks in Earth’s surface—composed of CO2, H2O, and some nitrogen

Roughly 100 times as much gas in this atmosphere than there is today, thereby being able to trap more heat

Oceans formed within 300 million years of Earth’s formation after the water in the atmosphere rained down onto Earth

The water absorbed half of the CO2 as well

Early plant life removed leftover CO2 via photosynthesis and produced O2

Formation of 3rd atmosphere

Oxygen is highly reactive; thus, the oxygen stayed at low concentrations by forming compounds with other elements (e.g.: iron)

About 2 billions years ago, after almost all possible elements had been paired with oxygen, the atmosphere filled up with it, thus forming the current, thinner atmosphere

Ultraviolet radiation

Double-edged sword

Originally, its penetration was beneficial as it provided energy for life to form in oceans

Amount hitting the Earth’s surface later had to be lessened in order to allow life to migrate from water to land

Formation of ozone layer allowed for this to occur

Ozone holes

Greenhouse gases Trap infrared radiation in Earth’s

atmosphere, thereby warming it as well as us

Surprisingly, water is the most abundant greenhouse gas, followed by carbon dioxide

Forms as a consequence of respiration but also from burning fossil fuels and leads to rising sea levels, increases in natural disasters, etc.

Plate tectonics

Plate tectonics Crust is made up of relatively low-density rock

that floats on top of a denser mantle

Theory of continental drift was ridiculed at first, but accepted after underwater mountain ranges were discovered

Exhibited “seafloor spreading” which is currently pushing America away from Africa at a rate of 3 cm per year

May form supercontinents, which in the past have broken apart and reassembled

Boundaries Three types: convergent (colliding),

divergent (separating), and slip-strike (grinding)

Subduction occurs at convergent boundaries when one plate slides under another

Reason why there are so few craters in the ocean—evidence of craters are erased via subduction

Earth’s interior

Formation Planetary differentiation: iron and other

dense elements sank towards the center of young Earth, while less dense materials were thrust upward

Generated a very dense central core surrounded by a less-dense mantle that lies underneath a thin crust of light minerals

Temperatures reach 9000 °F at the center of the Earth, but pressure is so high that heavy elements still remain solid

Movement Convection current—hot stuff rises, cools

down, and falls while the new hot stuff replaces it, cycle repeats

Occurs in Earth’s mantle and is the driving source of movement of tectonic plates

Magnetic field

Generation & Protection

Generated by hot molten iron convecting in Earth’s outer core as well as the planet’s rotation

Protects us from solar wind—electrically charged particles that are ejected from the sun’s atmosphere and move at a speed of 400 km/s

Sometimes the particles are trapped, forming two donut-shaped rings called Van Allen radiation belts and causing aurora borealis/australis

Craters Result from bombardment of meteoric

material from space

Pulverized rock from the crater site that is ejected into the crater’s surroundings is called an ejecta blanket—light-colored ones are newer than darker ones

The moon is locked in orbit around Earth, meaning one side always faces us and the other always faces away

The far side is much more heavily cratered

Maria Large, dark gray plains are called maria

because they were originally thought to be bodies of water

Formed by lava that filled in after most cratering ended; covers 17% of the moon’s surface

Rest of the moon is covered in light-gray, heavily cratered mountainous regions, dubbed highlands

Composition Lunar surface is covered in fine powder and

rock fragments—layer is called the regolith

Absorbs most incident light

Rock of low-lying lunar plains (mare) are called mare basalt

About 17% of the moon’s surface rock

Highlands are covered with light-colored rock called anorthosite

Interior Moonquakes occur because of:

Impacts

Motion of lunar surface b/c of Earth’s gravity

Expansion/contraction of surface due to heating/cooling

Other activity inside the moon

Small iron core, a layer of hot rock above it, and another layer of solid rock above that, then the crust

Anomalies Spacecrafts sent to the moon do not follow elliptical

paths—spacecrafts dip Moonward over a circular mare

Pulled by a higher concentration of mass (called mascons)

Local regions of relatively dense rock and metal near the moon’s surface

The moon’s slow rotation rate and tiny iron core should render its magnetic field weak, but there are still some spots where the field is strong enough to keep solar wind away—have yet to be explained

Origin Theories Fission theory—moon was pulled out from rapidly

rotating proto-Earth

Does not explain why the Moon’s composition mirrors the composition of Earth’s outer layers and not its core

Capture theory—moon was formed elsewhere and captured by the Earth

Difficult for such a large moon to be captured, also does not explain similar composition

Co-creation theory—moon was formed along with Earth

Doesn’t explain why compositions are different

Collision-ejection theory

The newly-formed Earth was struck at an angle by a Mars-sized asteroid

The debris from the impact began to orbit and cloud together, forming the Moon

Gave rise to the angle of rotation of Earth

Moon probably remained molten for thousands of years until the lava floating on the surface solidified into anorthositic crust

Tides Moon is in synchronous rotation around

Earth—rotates on its axis at the same rate that it and Earth orbit their barycenter

Tides in the ocean are created on both sides of the Earth when the moon, Earth, and sun are aligned (called spring tides)

We will die The moon is slowly spiraling away from Earth

Friction between the Earth and its oceans makes Earth rotate more slowly

Energy lost by Earth as it slows down is gained by the moon, making it spiral outward

However, the moon will never leave, because Earth’s rotation will slow down until it is synchronous w.r.t. the moon

Thereafter, the moon will remain at a fixed distance over one side of Earth

WHAT IF THE MOON DIDN’T EXIST

Delayed origins—it would’ve been much more difficult for life to form, as the tides that circulated minerals necessary for life to form would not have been created

Harsh conditions—continuous winds up to 150 mph would surround the planet due to its rapid rotation

No moonlight—animals might’ve evolved more heightened senses for use at night, or just wouldn’t have been nocturnal

Rush hour—only 6 hours in one day; different circadian rhythms

Wobbling Earth—rapid rotation causes large wobbling, which in turn causes catastrophic natural disasters and severe atmospheric/magnetic field changes

Puns A rise in mercury sometimes mars life on earth, how

else would nature planet?

His day job was astronomy but at night time he was moonlighting.

“I guess when your stars align/You do like the solar system and planet out”—Big Sean

How does the Earth get clean? It takes a meteor shower

Why does a moon-rock taste better than an earth-rock? Because it’s a little meteor.

MORE When the Sun and the planets die, one

person will receive the whole inheritance. Their lawyer convinced them to pursue a sole-heir system.

Two astronauts who were dating put an end to it because they both needed their space.

What do you call a tick on the moon? A luna-tick