What is the most important element for life on Earth?

• Nitrogen

• Hydrogen

• Carbon

• Oxygen

Over ______ billion years ago, life on earth existed ad single-celled microbes- bacteria.

• 3.5 billion

• 3.5 million

• 2.4 billion

• 2.4 million

For primitive bacteria on earth, oxygen was toxic.

• True

• False

What caused the "Great Oxygenation Event"?

• Evolution of Respiration

• Anaerobic Bacteria

• Evolution of Photosynthesis

The early atmosphere of earth had very little free __________.

• Carbon Dioxide

• Oxygen

• Nitrogen Gas

• Methane

The process of photosynthesis includes what two cycles?

• Oxygen and Nitrogen

• Carbon and Nitrogen

• Carbon and Oxygen

• Hydrogen and Carbon

_______________ are at the core of the cycling of matter in ecosystems on earth.

• Volcanoes

• Bacteria

• Food Webs

• Stromatolites