The human brain is more active during sleep than during the day.
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The oldest stone tools found are dated from 2.7 - 2.9 million years ago. The species that made these tools is unknown.
13
The human eye blinks an average of 4,200,000 times a year.
233
It takes about 20 seconds for a red blood cell to circle the whole body.
102
Tigers can see 6 times better at night than humans.
305
After age 30, the brain shrinks a quarter of a percent (0.25%) in mass each year.
139
The average person's skin weighs twice as much as their brain.
131
An average heart beats 100,000 times a day, pumping some 2,000 gallons of blood through its chambers. Over a 70-year life span, that adds up to more than 2.5 billion heartbeats.
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