EARTH SCIENCE

• Planet Earth is the home of every lifeform, known to us, in the universe
• Earth's age is about 1/3 of the age of the universe
• Earth is a slightly squashed fair with a heavy metal core, and a lighter surface crust, wrapped in a thin sliver of sweet air to breathe, with vast oceans, fertile plains, magnificent mountains, fresh water rivers, streams, lakes and aquifers, orbiting a star which warms us, and gives us energy
• How Earth came into existence

  1. 4.6 billion years ago, Earth was created from the remnants of dead stars, that collected in a giant, dirty gas cloud

  2. The gas cloud became denser in its center, and formed an accretion disk

  3. Small particles started clumping together, and building larger and larger objects, until they form the objects we call "Planets" today

  4. This process took 10 to 20 million years, and is still not very well understood
• A giant object, about as big as Mars, collided with Earth


  • The impact was violent, and if the object had been more massive, it might have destroyed Earth
  • Materials from Earth were smashed out into orbit, and formed the Moon, which is the biggest satellite in relation to its planet in the solar system
• At this time, Earth was a hot hell, constantly being hit by asteroids, with seas of lava, and a toxic atmosphere
• How Earth cooled down

  1. Water from the inside of the Earth wandered to the surface and rained down on Earth, only to vaporize again and become clouds

  2. Millions of asteroids brought more and more water to our planet
• Today, the surface of Earth is 71% water, and 29% land
• 97.5% of Earth's water is saline water, while only 2.5% is fresh water
• 69% of fresh water is ice and snow, 30% are ground waters, and only about 1% make up the remaining ground waters
• Only a tiny part of our water is actually lakes and rivers, and an even tinier part is bound in living things
• Plate Tectonics


  1. The crust of Earth consisted of separate giant plates that move around

  2. As they meet, they crumble, and create mighty mountains

  3. Or violently plunge back down, deeper into Earth, creating deep trenches
• The deepest hole ever drilled by man is 12.262 kilometers deep
• Crust


  About 50 kilometers thick, though it can vary between 5 and 70 kilometers
• Mantle


  A silicate rocky shell, and about 2,900 kilometers thick
• Upper mantle


  Has different regions, including the viscous "Lithosphere" that carries the crust, and the less mobile "Asthenosphere"
• Outer core


  A liquid layer of iron and nickel, about 2,266 kilometers thick, with temperatures varying from 4,000℃ to 5,700℃
• Inner core


  Mostly solid, a ball made of an iron-nickel alloy, with a radius of about 1,200 kilometers, and a temperature of the surface of the Sun
• The inner core is slowly growing at an estimated rate of about 1mm/year
• Earth's magnetic field


  An invisible phenomenon that diverts high energy particles coming from the Sun and other sources, allowing for a stable environment with comparatively little radiation impact on Earth
• The magnetic field is caused by large electrical currents flowing in complicated patterns in the core of Earth, in a system called the "Dynamo"
• Composition of dry air


  • Nitrogen
  • Oxygen
  • Argon
  • Carbon
  • Variable amount of water vapor
  • Small amounts of other gases
• Troposphere


  The lowest layer of the atmosphere, where the weather is, 12 kilometers thick on average
• Stratosphere


  Where the ozone layer protects us from the sun's most aggressive type of light
• Mesosphere


  The coolest place on Earth, with an average temperature around -85℃
• Thermosphere


  The transition to space, where Earth stops and space begins, at about 100 kilometers
• Ionosphere, aurora borealis, and the ISS


  Found in the Thermosphere
• Exosphere


  The outermost layer of the atmosphere, stretching up to 10,000 kilometers, merging fluently with outer space
• Humans, in their present form, have only been around for 200,000 years, which is 0.004% of Earth's history
• We are really lucky to be living in a thin, moist layer on a small, wet rock called Earth, which is the product of the universe's deepest workings, the result of a constant process of creation and destruction, happening all of the universe, all the time, helped by chance, the laws of the universe and random events
• In the past few billion years, Earth has been pummeled by asteroids, crashed into other planets, and frozen over several times, and has been ruled by all kinds of crazy life forms
• Our solar system began to emerge out of a dense cloud of interstellar gas and dust around four and a half billion years ago
• Formation of the solar system

  1. Cloud collapsed into a swirling disc of matter

  2. Matter got hotter and hotter until hydrogen fused into helium

  3. Birth of the Sun

  4. Formation of planets and moons
• Early Earth was incredibly active volcanically, spewing out gases like hydrogen sulfide, methane, and carbon dioxide
• Early Earth was constantly bombarded by large asteroids and comets
• A planet the size of Mars, called Thea, slammed into young Earth, throwing chunks of matter around Earth's orbit, which then formed the Moon
• 3.8 billion years ago, Earth cooled enough for water to condense and become liquid, forming the first primitive ocean
• Life appeared on Earth about 3.7 billion years ago, starting with microscopic organisms
• The first continents emerged from the ancient ocean, and the first supercontinent, Vaalbara, appeared on the planet
• Around 2.4 billion years ago, cyanobacteria evolved to become the planet's first photosynthesizers, producing oxygen and making Earth's atmosphere more hospitable