M1 L1: Characteristics of Earth

• The Earth has existed for 4.5 billion years. Because of the conditions during the time of life's earliest genesis, life was not possible. However, life grew over time, evolving from microscopic creatures into increasingly sophisticated species. In this lesson, we will discuss the different elements that make it feasible for life to exist on Earth.
• The environment on Earth supports a variety of living types. However, what are the distinguishing qualities of Earth that allow life to thrive on this planet? According to the Lunar and Planetary Institute (2019), the following are the factors that make a planet habitable:

  • temperature
  • water
  • atmosphere
  • energy
  • nutrients
• Temperature

  Influences how quickly atoms & molecules move.
• Not Enough of the Factor

  Low temperatures cause chemicals to react slowly, which interferes with the reactions necessary for life. Also, low temperatures freeze water, making liquid water unavailable.
• Just Right

  Life seems limited to a temperature range of minus 15°C to 115°C. In this range, liquid water can still exist under certain conditions.
• Too Much of the Factor

  At about 125°C, protein and carbohydrate molecules and genetic material (e.g., DNA and RNA) start to break apart. Also, high temperatures quickly evaporate water.
• Water

  Dissolves & transports chemicals within and to and from a cell
• Not Enough of the Factor (Water)

  The chemicals a cell needs for energy & growth are not dissolved or transported to the cell.
• Just Right (Water)

  Water is regularly available. Life can go dormant between wet periods, but, eventually, water needs to be available.
• Too Much of the Factor (Water)

  Too much water is not a problem, as long as it is not so toxic that it interferes with the chemistry of life.
• Atmosphere

  Traps heat, shields the surface from harmful radiation, and provide chemicals needed for life, such as nitrogen and carbon dioxide
• Not Enough of the Factor (Atmosphere)

  Small planets and moons have insufficient gravity to hold an atmosphere. The gas molecules escape to space, leaving the planet or moon without an insulating blanket or a protective shield.
• Just Right (Atmosphere)

  Earth & Venus are the right sizes to hold a sufficient-sized atmosphere. Earth’s atmosphere is about 100 miles thick. It keeps the surface warm & protects it from radiation & small-to-medium-sized meteorites.
• Too Much of the Factor (Atmosphere)

  Venus’s atmosphere is 100 times thicker than Earth’s. It is made almost entirely of greenhouse gasses, making the surface too hot for life. The four giant planets are completely made of gas.
• Energy

  Organisms use light or chemical energy to run their life processes.
• Not Enough of the Factor (Energy)

  When there is too little sunlight or too few of the chemicals that provide energy to cells, such as iron or sulfur, organisms die.
• Just Right (Energy)

  With a steady input of either light or chemical energy, cells can run the chemical reactions necessary for life.
• Too Much of the Factor (Energy)

  Light energy is a problem if it makes a planet too hot or if there are too many harmful rays, such as ultraviolet. Too many energy-rich chemicals are not a problem.
• Nutrients

  Used to build and maintain an organism’s body.
• Not Enough of the Factor (Nutrients)

  Without chemicals to make proteins & carbohydrates, organisms cannot grow. Planets without systems to deliver nutrients to their organisms (e.g., a water cycle or volcanic activity) cannot support life. Also, when nutrients are spread so thin that they are hard to obtain, such as on a gas planet, life cannot exist
• Just Right (Nutrients)

  All solid planets & moons have the same general chemical makeup, so nutrients are present. Those with a water cycle or volcanic activity can transport and replenish the chemicals required by living organisms.
• Too Much of the Factor (Nutrients)

  Too many nutrients are not a problem. However, too active a circulation system, such as the constant volcanism on Jupiter’s moon - Io, or the churning atmospheres of the gas planets, interferes with an organism’s ability to get enough nutrients.