Lecture 2: Origins of the Oceans

Today’s Focus Question:  Why is Earth the only planet in the solar system with liquid water?

This is a text version of the notes presented in class.

Feel free to email the instructor (dpalmer@kent.edu) with any
comments about the format and ease of use of these online notes.

1. Origins of the Oceans
- The Earth and Oceans Today

2. Comparison of planets - four inner "rocky" planets  Mercury, Venus, Earth, Mars,  four outer "gas giants"  Jupiter, Saturn, Uranus, Neptune, and the outermost planet Pluto which is small.

3.  The Earth Today - A Layered Planet
Today, materials in the Earth are layered
Lighter material are near the outside
Heavier materials are in the center

The layers are the atmosphere, the hydrosphere, the crust, the mantle, and the outer (liquid) and inner (solid) core
see Figure 3-6

4.  The diagram for H2O, shows liquid water at medium to high temperatures, gas at high temperature and low pressures, and solid ice at lower temps.  If you increase the temperature  on ice you go to liquid or gas depending on the pressure.  Increase of Pressure on ice makes it melt and decrease of pressure on ice makes it go into the vapor phase.

2. Our place in the solar system
Location, Location, Location
 -3rd planet out from the Sun, located between Venus (closer to the Sun) and Mars (further from the Sun)
 Earth is one of the rocky inner planets (Mercury, Venus, Earth and Mars), as compared to the large planets  beyond Mars, (Jupiter, Saturn, Uranus, Neptune, Pluto) that are composed of mostly of gas and ice.
 Let’s consider now why we have liquid water on Earth, as compared to our two nearest neighbors, Venus and Mars
 Water and its phases responding to temperature & pressure changes
 High atmospheric pressure (90 atm), High temperature 300 to 400 C) (Venus)
 Low atmospheric pressure, Low temperature (.01 atm, -200 to 20 C) (Mars)
 Moderate atmospheric pressure, Moderate temperature (Earth) (1 atm, -60 to 100 C)

 

3.  How do planetary density, composition, and gravity affect Earth’s hold on its water?
That is, how does Earth hold on to the liquid water?
Water Vapor (H20)  in the Atmospheres of Venus, Earth and Mars
Escape Velocities of Venus, Earth, and Mars (6 mi/sec, 7 mi/sec, and 4 mi/sec) (and compare to that of Jupiter (30 mi/sec)
 How fast do Hydrogen and Oxygen molecules travel?   Can they escape from Venus?  From Earth?  From Mars?  From Jupiter?
 


4.  Greenhouse gases:  Water vapor, Carbon dioxide, methane 

Venus has runaway greenhouse effect, Mars has CO2, but too thin an atmosphere for much heating

5.  Photos of Carbon dioxide ice cap changes show climate change is occurring on Mars today .

6.  Other places liquid water may exist is under the ice of Europa.

 

Summary:  Why is Earth the only planet in the solar system with liquid water?
 
•   Surface temperature and atmospheric pressure  permit all three phases of water (ice, liquid, vapor) to be present.
 
•   The gravitational field of the planet is strong enough to prevent oxygen and most hydrogen from escaping.  If Earth had less mass or was smaller in diameter, Earth would lose its atmosphere, And with the loss of atmospheric pressure, would lose the liquid water.

 

Where are scientists looking for evidence of extraterrestrial liquid water now?
 
   Below the surface of Mars, where ground water may exist.
 
   Below the ice of Europa, where an ocean may exist.
 
   In shaded spots near the poles on the lunar surface.
 

 

Preview of Next Lecture:  Exploration of the Oceans

Focus Question:  What are the major events in the exploration of the oceans?