To determine how long ago invertebrates became common on Earth, we'll analyze the geologic time scale provided in the table.
1. Identify the era and period where the event occurred:
- Era: Paleoroic
- Period: Selungn
- Key Event: Invertebrates become common
2. Compare the given event with the provided options:
- 1.6 million years ago
- 132 million years ago
- 410 million years ago
- 520 million years ago
Given that the event of invertebrates becoming common took place during the Selungn period of the Paleoroic era, the correct time frame, according to the available information, is:
410 million years ago.
Therefore, invertebrates became common on Earth 410 million years ago.