Scientists think that algae first evolved approximately 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere. Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.
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El agua contienentales conienen a ríos lagos glaciales y agua subterránea. Son corrientes de agua dulce que flullen en los continentes de las partes altas acia las bajas
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The answer is fundacion rotaria i think
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There can be 2 correct answers, (estoy detrás del )and (estoy enfrente del )
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