Acids have a ph of 6 and below whole bases have a ph of 8 and above. If a human has to much acid in their stomach they can take a pill that will lower it back to its normal ph level
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<h2>540 million years ago
</h2>
Paleozoic.
Era immediately follows Precambrian It lasted about 4.5 billion years.
When did abundant fossil evidence first appear in the geologic record.
540 million years ago.