Question

Select all of the answers that apply.

Answer 1

Answer:

the evolution of eukaryotic organisms

creating an ozone layer to shield life from UV rays

Explanation:

Cyanobacteria are the photosynthetic bacteria which increased in number in the pre-Cambrian period and produced a very high amount of oxygen.

This oxygen in the atmosphere mainly in the ionosphere reacted to form the ozone layer which protects against UV rays.

The organisms living during that period were mostly anaerobic that is were using other substrate molecules for respiration other than oxygen but due to increasing in concentration of oxygen about 75 % species became extinct and about 25% evolved to form the first animals or eukaryotes on Earth.

Thus, the selected options are correct.

Answer 2

Answer: creating an ozone layer to shield life from UV rays

Cynobacteria or blue green algae is the strain of bacteria, which was able to produce oxygen in the primitive earth as a result of photosynthesis. The abundance of oxygen in the atmosphere formed the ozone layer in the upper atmospheric layers, these layers are protective enough to provide a shield against the harmful UV radiations incident on earth coming from the sun.