July 5, 2018 Page 7
Thank the Moon for Earth’s Lengthening Day
Based on a Press Release from
the University of Wisconsin-Madison,
Provided by Bob Eklund
For anyone who has ever wished there
were more hours in the day, geoscientists
have some good news: Days on Earth are
getting longer.
A new study that reconstructs the deep
history of our planet’s relationship to the
Moon shows that 1.4 billion years ago, a
day on Earth lasted just over 18 hours. This
is at least in part because the Moon was
closer and changed the way the Earth spun
around its axis.
“As the Moon moves away, the Earth is
like a spinning figure skater who slows down
as they stretch their arms out,” explains
Stephen Meyers, professor of geoscience at
the University of Wisconsin-Madison and
co-author of the study published June 4 in
the Proceedings of the National Academy
of Sciences.
It describes a tool, a statistical method that
links astronomical theory with geological
observation (called astrochronology) to look
back on Earth’s geologic past, reconstruct the
history of the solar system and understand
ancient climate change as captured in the
rock record.
“One of our ambitions was to use astrochronology
to tell time in the most distant
past, to develop very ancient geological time
scales,” Meyers says. “We want to be able to
study rocks that are billions of years old in
rhythms. Scientists like Meyers have observed
this climate rhythm in the rock record, spanning
hundreds of millions of years.
But going back further, on the scale of billions
of years, has proved challenging because
typical geologic means, like radioisotope
dating, do not provide the precision needed
to identify the cycles. It’s also complicated
by lack of knowledge of the history of the
Moon.
Leap Seconds
Every now and then a leap second is added
to Coordinated Universal Time (UTC) in
order to synchronize clocks worldwide with
the Earth’s ever-slowing rotation.
Two components are used to determine
UTC:
International Atomic Time (TAI): A time
scale that combines the output of some 200
highly precise atomic clocks worldwide, and
provides the exact speed for our clocks to tick.
Universal Time (UT1), also known as Astronomical
Time, refers to the Earth’s rotation
around its own axis, which determines the
length of a day.
Before the difference between UTC and
UT1 reaches 0.9 seconds, a leap second is
added to UTC and to clocks worldwide.
By adding an additional second to the time
count, our clocks are effectively stopped for
that second to give Earth the opportunity to
catch up.
In Los Angeles, the most recent leap second
occurred on Dec. 31, 2016 at 3:59:60 p.m. •
Looking Up
During its flight to Jupiter in 1992, NASA’s Galileo spacecraft returned images of the Earth and Moon. Separate images were combined
to generate this view. NASA/JPL/USGS.
a way that is comparable to how we study
modern geologic processes.”
Earth’s movement in space is influenced
by the other astronomical bodies that exert
force on it, like other planets and the Moon.
This helps determine variations in the Earth’s
rotation around and wobble on its axis, and
in the orbit the Earth traces around the Sun.
These variations are collectively known
as Milankovitch cycles and they determine
where sunlight is distributed on Earth, which
also means they determine Earth’s climate
“Three things cannot be long hidden: the sun, the moon, and the truth.”
– Buddha
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