<u>Answer:</u>
Cyanobacteria start producing pure oxygen around 200 million years ago.
<u>Explanation:</u>
Many scientists believed that Earth did not have any oxygen. Cyanobacteria or the blue green algae are the microbes which produced oxygen for the first time with the help of photosynthesis. This was around 4.5 billion years ago: after Hadean eon.
They were very simple, but they produced oxygen in the early earth’s atmosphere. So, they brought evolution on earth. This “blue-green algae” exists in salt water, rocks and soils and play a major role in maintaining the ecosystem.
Answer:
A
Explanation:
I hope this helps. Sorry if i'm wrong.
Answer:
The correct phases would be
Homologous chromosomes are separated: It occurs during anaphase I of the meiosis I. It is the third phase of meiosis I during which homologous chromosomes are separated and pulled in opposite direction with the help of spindle fibers.
Homologous chromosomes are paired: It occurs during prophase I. The pairing of homologous chromosomes is termed as synapsis. The pairing is initiated in the zygotene stage of prophase I of the meiosis I.
Nuclear envelopes form around separated chromosomes: It occurs during the telophase I. It is almost opposite to the prophase I. After this phase, cytokinesis takes place.
The centrosome replicates: The replication of centrosome takes place during the S phase of the cell cycle. They migrate to the opposite ends during the prophase.