1. Life on Earth

2. Features of Earth That Allow for LIFE
OUR ATMOSPHERE -oxygen -water vapor -ozone (absorbs harmful UV) -carbon dioxide - nitrogen

3. EARLY EARTH
The early atmosphere was created by volcanoes releasing hot gasses. The gasses built up and created an atmosphere.
The early atmosphere was toxic and a human would not survive in it. 

4. WATER
-Over hundreds of thousandths of years the gases cooled, eventually reaching a temperature where clouds could release a toxic rainfall for thousandths of years.
-This is believed to be the source of half of the water in Earth's oceans today. 

5. Click the Early Earth for Water on Earth

6. SIDE NOTE:
Why is nitrogen the most common element in the earths atmosphere?
The answer lies mostly in three facts: nitrogen is volatile in most of its forms it is unreactive with materials that make up the solid earth it is very stable in the presence of solar radiation.

7. ORGANIC COMPOUNDS
As liquids built up on the planets surface, it further cooled the material, creating more stable land areas.
The ancient atmosphere was filled with poisonous gases, and the oceans were filled with organic molecules, such as amino acids, nitrogenous bases, and hydrocarbons setting up for life on Earth. 

8. Changing the Atmosphere and Oceans
Cyanobacteria are the key life forms that slowly changed Earth's oceanic and atmospheric chemistry to something hospitable to more complex forms of life.
These organisms are important because they are the first to photosynthesize, releasing oxygen into the shallow seas.
The earliest Stromatolite of confirmed origin dates to 2,724 million years ago. A recent discovery, however, provides strong evidence that microbial cyanobacteria existed as far back as 3,450 million years ago.

9. BANDED IRON FORMATIONS
The early oceans were also filled with heavy metals, specifically large amounts of Iron. 
As the first free oxygen was released by cyanobacteria, it bonded with iron dissolved in the oceans, forming thick iron- oxide (rust) layers on the ocean floor known as the Banded Iron Formations (BIFs) 

10. Eventually all of the Iron in the oceans had settled to the ocean floor and the era of the banded iron formations was complete.
With no Iron left to bond to, Oxygen was free to bubble out of the oceans and build up in the atmosphere.

11. SUITABLE RANGE IN TEMPERATURE
Earth “The Goldilocks Planet”

12. OUR Atmosphere Helps to keep us at a suitable temperature