Question

Which of these would be evidence that cyanobacteria evolved the ability to perform photosynthesis and released oxygen as a byproduct over 2 billion years ago? A) The presence of iron oxides (rust) in sedimentary rock layers that are 2 billion years old B) The presence of an iridium-rich layer in sedimentary rock dating from times of mass extinctions C) The presence of chloroplasts in fossilized eukaryotes from fossils dating from 2 billion years ago forward D) The formation of stromatolite rock structures from aggregates of cyanobacteria dating 3.5 billion years ago

Answer 1

A) The presence of iron oxides (rust) in sedimentary rock layers that are 2 billion years old.

Step-by-step explanation:

Cyanobacteria perform photosynthesis using sunlight, water and carbon dioxide to produce carbohydrates as well as oxygen. In fact, to this day, all plants on Earth contain cyanobacteria - known as chloroplasts - that participate in photosynthesis. This is how oxygen arrived on earth over 2 billion years ago.

A great evidence of this moment is the presence of iron oxides (rust) in 2 billion year old sedimentary rock layers. Since it is the first report of an element that has oxygen in its composition.

Answer 2

A) The presence of iron oxides (rust) in sedimentary rock layers that are 2 billion years old.

Step-by-step explanation:

• Cyanobacteria are aquatic and photosynthetic ,they live in water and manufacture own food releasing oxygen as a by product and in which most living organisms depend on.

• Cyanobacteria are found in the ocean and are believed to be responsible for the formation of the iron oxide found on the sedimentary rocks since they release oxygen as a by product and it is used in the iron oxide formation process below the level of wave disturbance.