Objective:Objective: ExplainExplain the development of the development of Earth’s atmosphere Earth’s atmosphere and the influence of and the influence of

early life on the early life on the atmosphere.atmosphere.

•Formation of Formation of the Earth’s the Earth’s AtmosphereAtmosphere

•Early AtmosphereEarly Atmosphere •Scientists think that the Scientists think that the Earth’s Earth’s earlyearly atmosphere atmosphere was a mixture of was a mixture of gasesgases that were released as the that were released as the Earth cooled.Earth cooled.

•During the final stages of During the final stages of the Earth’s formation, its the Earth’s formation, its surface was very surface was very hothot——even molten in places. even molten in places. The molten rock released The molten rock released large amounts of large amounts of carboncarbon dioxide and dioxide and waterwater vapor. vapor.

•Changing Changing AtmosphereAtmosphere

•As the Earth As the Earth cooledcooled and and its layers formed, the its layers formed, the atmosphere changed atmosphere changed again. This atmosphere again. This atmosphere probably formed from probably formed from volcanicvolcanic gases.gases.

•Volcanoes released Volcanoes released chlorinechlorine, nitrogen, and , nitrogen, and sulfursulfur, and large amounts , and large amounts of carbon dioxide and of carbon dioxide and water vapor. This water water vapor. This water vapor may have vapor may have condensedcondensed to form the to form the first oceans.first oceans.

•Comets, which are Comets, which are made of made of iceice, may , may have contributed to have contributed to this change of this change of Earth’s atmosphere.Earth’s atmosphere.

•As they As they crashedcrashed into into the Earth, comets the Earth, comets brought in a range of brought in a range of elements, such as elements, such as carbon, hydrogen, carbon, hydrogen, oxygen, and nitrogen.oxygen, and nitrogen.

•Comets also may Comets also may have brought some have brought some of the water that of the water that helped form the helped form the oceansoceans..

•The Role of LifeThe Role of Life

• Ultraviolet RadiationUltraviolet Radiation • Scientists think that Scientists think that

ultraviolet (ultraviolet (UVUV) radiation ) radiation helped produce the helped produce the conditions necessary for life. conditions necessary for life.

• UV light has a lot of UV light has a lot of energyenergy and can and can breakbreak apart apart molecules.molecules.

• Earth’s early atmosphere Earth’s early atmosphere probably did not have the probably did not have the protection of the protection of the ozoneozone layer layer that now shields our planet that now shields our planet from most of the sun’s UV from most of the sun’s UV rays. So many of the rays. So many of the molecules in the molecules in the airair and at and at the surface were the surface were brokenbroken apart by UV radiation.apart by UV radiation.

• Over time, broken down Over time, broken down molecular material molecular material collectedcollected in the Earth’s in the Earth’s waters, which offered waters, which offered protection from UV protection from UV radiation.radiation.

• In these sheltered pools of In these sheltered pools of water, water, chemicalschemicals may have may have combined to form the combined to form the complex molecules that complex molecules that made made lifelife possible. possible.

• The first life-forms were The first life-forms were very very simplesimple and did not and did not need need oxygenoxygen to live. to live.

• Sometime before 3.4 billion Sometime before 3.4 billion years ago, organisms that years ago, organisms that produced food by produced food by photosynthesisphotosynthesis appeared. appeared. Photosynthesis Photosynthesis is the process is the process of of absorbingabsorbing energy from the energy from the sun and carbon dioxide from sun and carbon dioxide from the atmosphere to make the atmosphere to make foodfood..

• During the process of During the process of making food, these making food, these organisms organisms releasedreleased oxygen—a oxygen—a gasgas that was that was not abundant in the not abundant in the atmosphere at the time.atmosphere at the time.

• Photosynthetic Photosynthetic organismsorganisms played a major role in played a major role in changing Earth’s changing Earth’s atmosphere to become the atmosphere to become the mixture of mixture of gasesgases it is it is today.today.

• Over the next hundreds of Over the next hundreds of millions of years, more millions of years, more oxygenoxygen was added to the was added to the atmosphere while atmosphere while carboncarbon dioxide was removed.dioxide was removed.

• As oxygen levels As oxygen levels increasedincreased, some of the , some of the oxygen formed a layer of oxygen formed a layer of ozoneozone in the upper in the upper atmosphere. atmosphere.

• The ozone The ozone blockedblocked most most of the UV radiation and of the UV radiation and made it possible for life, in made it possible for life, in the form of simple the form of simple plantsplants,, to move onto land about to move onto land about 2.2 billion years ago.2.2 billion years ago.

Today’s atmosphere

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