Question

Based on paleontological evidence, eukaryotic organisms are estimated to have first evolved:

• A. more than 750 million years ago.
• B. 750 to 500 million years ago.
• C. 500 to 250 million years ago.
• D. 65 million years ago.

Hint:

To understand evolutionary timelines:
1. Single-celled eukaryotes emerged approximately 1.6 to 2.1 billion years ago.
2. Multicellular eukaryotes appeared more than 750 million years ago.
3. Always match the timeline to the context provided in the question.

Answer 1

The Correct Option is A

Step 1: Timeline of eukaryotic evolution. Eukaryotic organisms are characterized by the presence of a nucleus and membrane-bound organelles. Based on fossil evidence, the first eukaryotic cells are believed to have appeared approximately 1.6 to 2.1 billion years ago, with multicellular eukaryotes emerging more than 750 million years ago. Step 2: Evaluate the options. Option (A): This is correct. Multicellular eukaryotic organisms appeared more than 750 million years ago, during the Precambrian era.
Option (B): This is incorrect. By 750 to 500 million years ago, eukaryotes were already well-established, and many complex multicellular organisms had evolved.
Option (C): This is incorrect. This period corresponds to the Paleozoic era when advanced multicellular life forms (e.g., plants and animals) became more diverse.
Option (D): This is incorrect. 65 million years ago corresponds to the mass extinction event that wiped out the dinosaurs, long after eukaryotes had evolved.