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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[b]{2}{}{Cenozoic} & Quaternary & & \multirow{4}{}{\begin{tabular}{l}
Humans evolve \\
Extinction of \\
Dinosaurs
\end{tabular}} \\
\hline & Tertiary & & \\
\hline \multirow[b]{2}{}{Mesozoic} & Cretaceous & & \\
\hline & [tex]$\frac{\text{Jurassic}}{\text{Triassic}}$[/tex] & & \\
\hline \multirow{6}{}{Paleozoic} & \begin{tabular}{l}
Permian \\
\end{tabular} & & \multirow{6}{}{\begin{tabular}{l}
Permian mass \\
extinction \\
Invertebrates \\
become common
\end{tabular}} \\
\hline & Carboniferous & & \\
\hline & Devonian & & \\
\hline & Silurian & & \\
\hline & Ordovician & & \\
\hline & Cambrian & & \\
\hline Proterozoic & \multirow{3}{}{\begin{tabular}{l}
Also known \\
as \\
Precambrian
\end{tabular}} & & \multirow{3}{*}{\begin{tabular}{l}
Earliest life
\end{tabular}} \\
\hline Archean & & -3500 & \\
\hline Hadean & & & \\
\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



Answer :

GinnyAnswer
To determine when invertebrates became common on Earth, we need to analyze the information provided in the geologic time scale.

1. The time scale is divided into different eras: Cenozoic, Mesozoic, Paleozoic, Proterozoic, Archean, and Hadean.

2. Under the "Paleozoic" era, there are several periods listed: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

3. The key event we are focusing on is when "Invertebrates become common", which is indicated to have occurred during the Cambrian period within the Paleozoic era.

4. To find the specific time period in years, we need to identify how many millions of years ago the Cambrian period occurred. Based on geological time scales, the Cambrian period is known to have occurred approximately 520 million years ago.

Therefore, the correct answer is:
520 million years ago

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