• What does it mean to be alive?

Investigation 2.2Is it Alive?

• Uses Energy• Exchanges gasses• Responds to Stimuli• Reproduce• Grow & Develop

So, what planets have these vital conditions/characteristics?

EARTH

• The Sun’s proximity (distance from Earth) to Earth makes Earth a good candidate for supporting life.

• At this distance, Earth receives just the right amount of radiant energy.

• The main factor affected by this radiant energy is TEMPERATURE.

• Earth’s temp. is 130oF – 160oF

• Earth has an abundance of the element Oxygen.

• Oxygen is a component of many, many vital compounds organisms use to carry out life functions.

• One such vital compound is H2O

• Earth has plenty of liquid water

• Earth’s temperature range allows for liquid water to exist over much of the planet.

• All organisms on Earth use water in unique ways

Earth is just right

• Mercury, Venus, and Mars are too hot or too cold for liquid water to exist.

• (PROXIMITY to the SUN)

• The human body is 60% to 75% water.

• Liquid water is used to transport food and nutrients where they need to go, inside and outside of cells.

Why liquid water is important

• Water is a good solvent.

• A solvent is a substance that is capable of dissolving another substance.

Importance of water

• Filters Radiation

• Protects Earth from Collisions

• Traps Heat (protects from freezing temperatures, especially at night)

• Nitrogen (N2) gas makes up about 78% of Earth’s atmosphere.

• Nitrogen is a vital element for living things.

• An atmosphere is a layer of gases surrounding a planet or other body in space.

• The atmospheres of Venus, Earth, and Mars were formed in similar ways, so we might expect them to contain similar elements.

Comparing atmospheres

Changing the atmosphere

• Through photosynthesis, life on Earth has actually changed the planet’s atmosphere.

• Gravity holds our atmosphere to Earth. Without it, our atmosphere would float away.

• Gravity keeps atmospheric gasses in propper layers. Heavy gasses near the surface, lighter gasses away from the surface.

• Gravity keeps things grounded (dirt, trees, water, you)