Conditions for Life on Earth

• The Earth’s mass creates a specific gravitational force.

  This pull of gravity prevented gases from escaping into space and allowed an atmosphere created.
• The atmosphere is made up of many gases, including carbon, hydrogen, oxygen and nitrogen – all of which are key components of life.

  These important life sustaining gases were not found isolated in the early Earth.

  Instead, they were present in compounds such as: ammonia, methane and carbon dioxide.
• The mass of the Earth and gravity lead to the formation of the atmosphere
• Atmospheric pressure and temperature maintained liquid water
• Water is a solvent - most chemical reactions in living organisms involve a reaction in water
• Water is important for transport within organisms - blood and sap transport dissolved sugars, amino acids, mineral nutrients and waste products in plants and animals.
• Water is important for temperature control - as water evaporates, it absorbs heat. This causes temperatures to decrease.
• Water is important because it expands when frozen - water is most dense at 4*C - and water cooler than this will float, this stops the convection current and prevents a whole body of water from extreme cooling.
• Water is important for aquatic habitats as it is the home to aquatic species
• Water is important for the absorption of UV radiation - prior to the formation of the ozone layer the oceans protected aquatic species from the sun's radiation, allowing species to develop and thrive.
• Insolation is the amount of solar radiation received on a given surface in a given time period.
• Albedo is a measure of the amount of light reflected off the surface
• Global Warming is the temperature increase of the Earth’s atmosphere and surface.
• Climate Change is the long-term changes to the climate patterns due to prolonged periods of warming.
• The Earth is at a distance from the sun we often refer to as the

  “Goldilocks zone”

  The Earth’s orbit maintains a distance that is warm enough to sustain life
• The angle of the axis of rotation produces our seasonal variations in weather conditions. The angle of the Earth’s tilt is 23.5 degrees
• The magnetosphere was formed as the Earth has a solid inner core and a liquid outer core, both made of iron and nickel. The metal carries an electrical current that is powered by the movement of the liquid. As Earth spins on its axis, the iron inside the liquid outer core moves and this causes powerful electric currents to develop in the liquid iron itself. These currents create the magnetic field which surrounds the Earth.
• Oxygen was produced when all life started out in the ocean around 2.7 billion years ago. Archaea in the ocean had developed the ability to perform photosynthesis and for the next several million years all of the oxygen reacted and remained within the oceans. Eventually excess oxygen was released into the atmosphere. This is the first-time earth had free, breathable oxygen in its atmosphere. Gradually the oxygen in the atmosphere built up and began to absorb ultraviolet light, so life could develop. During this time period, the concentration of oxygen in our atmosphere was up to 31%.
• The percentage of oxygen in the atmosphere today is 21%.
• Ozone is O3 or 3 oxygen molecules
• The ozone layer is found at the bottom of the stratosphere. It's found here because it is the optimum conditions, as there is too little UV light in the troposphere and too little oxygen at the top of the stratosphere.
• The stratosphere is warm because it's heated from above by UV radiation.
• Carbon sequestration is a process by which carbon is removed from the atmosphere and then stored in either a solid or liquid form.
• A biogeochemical cycle is a cycle of matter. It is the movement and transformation of matter between living organisms, the atmosphere and the Earth’s crust. There is only a finite amount of life-supporting nutrient elements, these cycles make it possible for life to survive over a long-time period, without the resources becoming completely depleted.
• The fast carbon cycle is when CO2 is absorbed by phytoplankton by photosynthesis, then it is transformed into carbohydrates and stored in their tissues. Respiration by living organisms' releases CO2 to the atmosphere and the decomposition of the organism when it dies releases CO2 back into the ground.
• The slow carbon cycle is when marine organisms, such as shellfish and phytoplankton, build their shells by combining calcium with carbon. When they die they accumulate on the ocean floor and over millions of years become compressed and form carbon-rich sedimentary rock: this carbon is usually stored in rocks for around 150 million years. Oceanic crust, containing sedimentary rock, is subducted causing the crust to melt and the CO2 that was stored in the rock is released into the atmosphere through volcanic eruptions.
• The basic nitrogen cycle is:

  • Plants absorb nitrogen
  • Bacteria in the roots and soil convert nitrogen into ammonia
  • Animals take in nitrogen in the form of proteins 
• All biogeochemical cycles involve living organisms because they prevent the build up of waste materials and prevent a shortage of resources. It is important that species developed and evolved for the stability of the whole planet and varied ecosystems within.
• Around 4 billion years ago, Mars' core became inactive and it's magnetic field dissipated. With it's protection lost, solar winds and radiation stripped away the water and atmosphere. Without a magnetosphere, biologically damaging UV radiation reaches the surface, preventing life from forming or surviving.