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Study this image of a geologic time scale.

\begin{tabular}{|c|c|c|c|}
\hline ERA & PERIOD & \begin{tabular}{l}
MILLIONS OF \\
YEARS AGO
\end{tabular} & KEY EVENTS \\
\hline \multirow{2}{}{ Cenozoic } & Quaternary & \multirow{3}{}{\begin{tabular}{l}
[tex]$1.6=\cdots$[/tex]
\end{tabular}} & \multirow{5}{}{\begin{tabular}{l}
Humans evolve \\
Extinction of \\
Dinosaurs
\end{tabular}} \\
\hline & Tertiary & & \\
\hline \multirow{3}{}{ Mesozoic } & Cretaceous & & \\
\hline & Jurassic & \multirow{2}{}{\begin{tabular}{l}
[tex]$132=\cdots$[/tex]
\end{tabular}} & \\
\hline & Triassic & & \\
\hline \multirow{5}{}{ Paleozoic } & Permian & \multirow{3}{}{\begin{tabular}{l}
[tex]$339=\cdots$[/tex]
\end{tabular}} & \\
\hline & Carboniferous & & \\
\hline & Devonian & & \\
\hline & Silurian & & \multirow{3}{}{\begin{tabular}{l}
Invertebrates \\
become common
\end{tabular}} \\
\hline & Ordovician & & \\
\hline \multirow{2}{}{ Precambrian } & Proterozoic & \multirow{2}{}{\begin{tabular}{l}
[tex]$3500=\cdots$[/tex]
\end{tabular}} & \\
\hline & Archean & & \\
\hline
\end{tabular}

How long ago did invertebrates become common on Earth?

A. 1.6 million years ago
B. 132 million years ago
C. 410 million years ago
D. 520 million years ago

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Answer :

GinnyAnswer
To determine the period during which invertebrates became common on Earth, we need to refer to the provided geologic time scale. From the table and key events listed, we observe the following:

1. The geologic periods are listed in the middle column.
2. The key events associated with these periods are described in the rightmost column.

From the table:
- We note that the event specified as "invertebrates become common" is listed during the Ordovician period within the Paleozoic era.

Knowing this, we match the Ordovician period to its corresponding time frame on the geologic scale, which indicates that:

- The Ordovician period occurred approximately 410 million years ago.

Therefore, the correct answer is:

410 million years ago

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