Approximately how many years ago did invertebrates become common on Earth?

• A. About 600 million years ago
• B. About 10,000 years ago
• C. About 2 billion years ago
• D. About 65 million years ago

Answer: (A)

Verified step by step guidance

1. Understand the context of the question: Invertebrates are animals without a backbone, and their emergence is a significant event in Earth's evolutionary history. This question is asking about the approximate time when invertebrates became common.
2. Recall the timeline of Earth's history: Life on Earth began approximately 3.5 billion years ago, and multicellular organisms started appearing around 1 billion years ago. Invertebrates became common during the Cambrian Explosion, a period of rapid diversification of life forms.
3. Identify the Cambrian Explosion: The Cambrian Explosion occurred approximately 541 to 485 million years ago, marking the time when invertebrates became widespread and diverse.
4. Eliminate incorrect options: About 10,000 years ago refers to the recent past, not relevant to invertebrates. About 2 billion years ago is too early for multicellular life. About 65 million years ago refers to the extinction of dinosaurs, not the emergence of invertebrates.
5. Select the correct answer: Based on the timeline, the correct answer is 'About 600 million years ago,' as it aligns with the Cambrian Explosion when invertebrates became common.