1. The “Spheres” of the Earth
SNC 1D - Ecology

2. The Earth is Unique
In all of the known universe there is only 1 planet that is known to hold life.
In our solar system, it is the only planet has all the requirements to sustain life as we know it.
The Earth orbits approximately 1.5 x 108 km from the sun, and is surrounded by a thin layer of gas.
Earth is unique because it supports many different habitats.
A habitat is the natural environment in which a plant, animal (etc.) lives.
The Earth’s habitats include both terrestrial (land) and aquatic (water) areas.

3. The Atmosphere
The strength of Earth’s gravity (caused by its size) holds a layer of gasses near the surface.
This layer of gasses is known as the atmosphere.
The atmosphere is made up of several parts:
78% Nitrogen
21% Oxygen
1% other gasses
The atmosphere acts as an insulator, keeping the surface at an average temperature of 15˚C.
The atmosphere blocks some solar radiation.

4. The Atmosphere The atmosphere is made up of multiple levels.
Troposphere
Stratosphere
Mesosphere
Thermosphere

5. The Lithosphere The lithosphere is the rocky outer shell of the Earth.
It is made up of rocks and minerals.
It forms mountains, ocean floors, and all of Earth’s solid landscape.
The lithosphere ranges from (approximately) 50 to 150 km in thickness.
The lithosphere has many layers.

6. The Hydrosphere
The hydrosphere is all the water on, above, and below the Earth’s surface.
It includes oceans, rivers, lakes, groundwater, clouds, etc.
Nearly all of the Earth’s water (about 97%) is contained in the oceans.

7. The biosphere
The term biosphere is used to describe anywhere that life can exist.
It includes any/all parts of the atmosphere, lithosphere, and hydrosphere that support life.
Most life is seen on the Earth’s surface and in the oceans, but many micro-organisms can live several km below the surface.
While the Earth is large, the biosphere is small (in comparison).
Living things need the right combination of hydrosphere, lithosphere, and atmosphere to survive.

8. The Biosphere

9. The Gaia Hypothesis
In the 1960s some scientists put forward the idea that the combination of hydrosphere, lithosphere, and atmosphere allows Earth acts like a living organism.
This theory is not well supported scientifically, but is often used to educate people on the effects of damaging the Earth’s spheres.
When people think of the Earth as a whole as a living thing they are less likely to act recklessly.

10. Your Turn
Define the terms: lithosphere, biosphere, hydrosphere, and atmosphere.
How does the existence of an atmosphere enhance life on Earth?
Using a chart, drawing, or words, describe ways in which the spheres overlap each other.
What is the benefit of using the Gaia hypothesis, even though we know it isn’t fully correct?
What surprised you the most about the physical makeup of the Earth’s spheres, and the relationships between them?
Using what you know about the Earth, explain why the Moon has no atmosphere.