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For these questions, refer to the graph below, which shows atmospheric O2 levels throughout Earth's history 3. 35 O2 levels were almost 50% higher than present. Giant flying insects 30 Invasion First of land chordates 25 First plants 20 First eukaryotes 15 First photosynthetic multicellular cyanobacteria eukaryotes 02 levels were 25-40% lower than present. O 10 Rapid drop of 02 levels occurred at end of the Permian. First 5 irst lite bacteria 0 4,000 3,000 2,000 100 1,000 Millions of years ago 500 250 LIFE: THE SCIENCE OF BIOLOGY 11e, Figure 24.8 O2017 Sinaser Associates, Inc. Photosynthesis evolves after the first evidence of life. If they were not photosynthetic, how did the first organisms obtain sugar for respiration? a. The first evidence of aerobic respiration occurs about 2 billion years ago. Why did aerobic respiration arise after photosynthesis? If the first living organisms were not aerobic, how were they able to perform respiration? b. Why do we see an increase in O2 levels following the invasion of land? What wa the terrestrial landscape like at this time? c. d. Why do O2 levels drop so significantly 250 mya? Why do we not see similar dreps 444 mya, 359 mya, 201 mya, or 65 mya?

Answer 1

The first organism were coacervates this are heterotrophic anaerobes since, there was virtually no oxygen in environment at that particular period this bacteria needed to be anaerobic they will not use oxygen for breathing , this heterotrophic organism weren’t able to prepare their food material they dependent on all food material that was available in nature and feed on them.
Respiration uses oxygen and produces carbon dioxide. Photosynthesis uses carbon dioxide and produces oxygen
During land invasion a lot of tressterial land was covered by trees plant animals since trees do photosynthesis the oxygen level peak was show in this era.

The coacervated were first organism which were anaerobic do not need oxygen to grow and where heterotrophic in nature. Finally they were following prokaryotes and aerobic organism growth.

The Permian period , Palaeozoic era was around 299 million years ago
let had lot of swamp so oxygen levels 50% high than present at the end of the period about 250 million year ago the various continents aggregated to form and make Pangaea and O2 levels drop rapidly due to it also mass extinction .

Also the was extinction to 90 percent of species in 250 mya due to which the oxygen level depleted significantly.