Ballpark — October 2, 2026
Answers to that day's 5 daily estimation questions.
How many years can a Greenland shark live, according to scientists' best estimate?
~400 years
Scientists estimated their age using radiocarbon dating of proteins in the eye lens.
About how many neurons are in the human brain?
~86 billion neurons
The commonly quoted '100 billion' figure was never actually based on a real count — the real number is closer to 86 billion.
About how many stars does the Milky Way galaxy contain?
~100 billion stars
Astronomers can't count them directly — they estimate the total from the galaxy's overall mass.
How many detectable earthquakes does the Earth produce worldwide in an average year?
~500,000 earthquakes
Of those, only around 100,000 are strong enough for people to actually feel.
Counting every wall, branch, and natural barrier built over 2,000+ years, how many miles long is the Great Wall of China in total?
~13,175 miles
China's 2012 government survey measured every wall, trench, and natural defensive barrier built across multiple dynasties.