So, if we say something is 1 billion years old, is that (365 spins on earth’s axis x 1 billion)? Is it (1 trip around the sun x 1 billion), or a different measurement? The answers to those change depending on how it’s calculated.
In other words, if I say I lived one year, that means 24 hr/day for 365 days/year in todays terms. Over time the earth’s orbit of the sun becomes faster and slower changing the meaning of a year. Also, as the earth spins faster and slower on its axis, a day in terms of hours is different relative to today. It breaks my brain.
What about the needs for adjustments for leap years? How does this influence radiometric dating? If a molecule degrades by 1 measurement every 300,000 years, the first 150,000 years are going to be different than the last half. If you want to pinpoint the halfway mark, where is it?
In: Planetary Science
It would be 1 billion years ago with the current lenght of a year. I am not 100% sure what definition of yar is used but I would assume it is a Tropical year that is close to 265.25 days. That way leap days get included. The accuracy of measurement is not down to days. the making of error is typically +-2 to 5% for radiocarbon dating so at 1000 years it is 20 years before or later at 2% and 50 years at 5%. Radiometric dating methods in geological time scale can have a margin of error of millions of years.
It is by the way not 365 rotations of Earth’s axis, Earth rotates relative to far away stars once in 23 hours and a bit more the 56 minutes the extra 4 minutes is because Earth has moved a bit relative to the sun and Earth needs to rotate more then 1 revolution for the sun to return to the same point in the sky.
Consider a nonrotation earth that orbits the sun, the sun would move around once in the sky because of the orbit. 4 minutes times 365 days is 24 hours and a half our. It would be very close to 24 hours if we used the exact length. So Earth rotates close to 366 revolutions in 365 days.
A year is not an orbit of the earth around the sun either. It is a cycle of the season on earth like the time between two march equinoxes. The diffrence is because the precision of earth axis and is around 20 minutes per year. It might not sound like a lot but it is a day in 72 years. It result is exactly the location of stars changes and it can be a lot over time. The Zodiac is based on the stars behind the sun when you observe it from earth. If you compare typical dates for the signs of the zodiac to where the sun really is you will se they typically do not match, it is closer to a shift of one sign because the dates are from over 1000 years ago.
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