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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
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