when a persons heart beat is not normal is typically let's say 60-100 beats per minute that means the blood is not pumped properly throughout the body. so the pacemaker works as an heart machine to keep your heart beating.
For the answer to the question above, I believe the answer is "Tertiary Period" <span>The Tertiary Period marks the beginning of Cenozoic Era. It only began 65M years ago and lasted more than 63M years, until 1.8 million years ago.</span>I hope my answer helped you. Have a nice day!
