Legacy Test 1 – Fossil Discovery Indicates Multicellular Development’s Origin on Earth
A fascinating new discovery offers “tantalizing” evidence for the origin of
multicellular development in life on Earth.
It seems related to something that had perhaps never happened before, and
certainly has never happened since: a near-total collapse of the Earth’s
magnetic field.
650 million years ago, there was little going on across the Earth worth writing
about, but shortly after, when multicellular life did begin to emerge and
diversify in a period known as the Edicarian, it started within a 26
million-year window of time when the Earth’s magnetic field plummeted to
one-thirtieth its current strength.
The authors of this geologic discovery from the University of Rochester point
out that this would have driven a rapid decrease in hydrogen content in the
Earth’s atmosphere and rapidly increased oxidization of the air and oceans,
allowing metabolically demanding activities like movement and propulsion to
become more and more possible.
The Edicarian Period, lasting from 635 to 565 million years, currently offers
the oldest confirmed fossil evidence of multicellular life on Earth. For their
time they were both diverse and complex, but in comparison to any other epoch,
they were extremely primitive, and consisted mostly of tubular and frond-shaped
creatures but also some that had developed locomotion, including the earliest
jellyfish.
Generated by the molten iron core of Earth, the magnetic field is essential for
life. It does something far more important than make our compasses work or
create the Aurora Borealis, it protects the planet from streams of radiation
coming off the Sun called solar wind.
“Oxygen has long been identified as a key “environmental gatekeeper,” allowing
for evolutionary innovation and for meeting the energy demands of animals,” the
authors write.
“Although sponges and microscopic animals can survive at low levels of dissolved
oxygen, macroscopic, morphologically complex, and mobile animals require a
greater amount of oxygen to support their metabolic demands.”
A weakened magnetic field would allow the Sun’s radiation to strip away lighter
molecules like hydrogen from the Earth’s atmosphere, and hydrogen can enter
space through non-thermal processes as well. This could have resulted in an
increase in oxygen sufficient enough to allow early macroscopic life to evolve
in the sea.
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Study author Professor John Tarduno and the co-authors describe the association
between the earliest forms of complex life and this fall in the magnetic field,
which they discovered through a particular kind of crystal called plagioclase
which records magnetic signatures superbly well, as “tantalizing but unclear.”
In their study, the scientists point out that oxygen content in samples of life
from the Edicarian period is significantly higher than in samples from previous
periods.
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The team previously discovered that the geomagnetic field recovered in strength
during the subsequent Cambrian Period, when most animal groups began to appear
in the fossil record, and the protective magnetic field was reestablished,
allowing life to thrive.
“If the extraordinarily weak field had remained after the Ediacaran, Earth might
look very different from the water-rich planet it is today: water loss might
have gradually dried Earth,” Tarduno told Rochester Univ. press.
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