It Is Difficult to Estimate When Cyanobacteria Appeared on Earth

question 37

Multiple Choice

It is difficult to estimate when cyanobacteria appeared on Earth using the evidence from the oxidation state of the Earthʹs crust because

• A) several ancient anaerobic metabolisms require O₂.
• B) there are multiple forms of anoxygenic photosynthesis.
• C) there are multiple groups of oxygenic photosynthetic bacteria.
• D) several ancient anaerobic metabolisms form Fe³⁺ without requiring O₂.

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Definitions:

Zygote

The initial cell formed when two gamete cells are joined by means of sexual reproduction, representing the earliest developmental stage of the embryo.

Teratogens

Any agent that can cause developmental malformations (birth defects) in an embryo or fetus.

Prenatal

Pertaining to the period before birth, from conception to the onset of labor.

Newborns

Infants in their first few hours to weeks of life, particularly before they are one month old, encompassing the very early stages of development.