What Was The Earth Like 1 Billion Years Ago? When Life Stopped
Over time, our planet has been shaped by many monumental events.
From the Cambrian explosion of life some 540 million years ago, when most animal
forms appeared, to the rise and fall of the dinosaurs, the dramatic course of biological
evolution is well documented in the fossil record. But the Earth has also lived through largely
obscure and little-known geological eras. In this video, we want to tell you about a
long period that is almost completely devoid of fossil evidence. This is not because we cannot
find the rocks in which life might have left its footprints, but because throughout billions of
years, all geological and biological processes seemed to have ceased or greatly diminished.
A billion years is a long time, even on a geological scale-it's more than one-fifth
the age of the Earth-where did it end? How is it possible that we know so little about it?
Well, we can't give away any spoilers, but you should know that we're talking
about a billion-year period that began in the middle of the Proterozoic Era.
How can we define it? A period of darkness, a black hole in history? The missing chapter
in Mother Earth's great book? We don't need to worry about
it. Someone before us has already thought of calling it what it deserves to be called...
But how? Well, to find out, just keep watching the video!
First, though, allow us to bore you (you really should believe us) with a quick summary of Earth's
past, necessary to focus on times and situations. You should know that for the first 600 million
years, in the eon called the Hadean, the Earth was a kind of glowing ball in a molten state.
Later, during the Archean eon, the surface of the Earth, as it cooled,
allowed the formation of a crust and continental plates, and the accumulation of a large amount of
water that formed the first oceans. As early as 3.7 billion years ago,
the first forms of life appeared: single-celled organisms without nuclei, called prokaryotes,
but it was not until the Proterozoic Era, from 2.5 billion to 541 million years ago,
that more complex single-celled organisms appeared, such as eukaryotes with nuclei,
and the first multicellular forms... And our story begins right in the middle of the Proterozoic
Era... At the beginning of those billions of years about which almost nothing is known…
If we could explore the surface of the Earth a billion years ago, the aspect that would
strike us most would be its "flatness", both altimetrically and environmentally.
In fact, we would see no trees, no hills or mountain ranges.
Not to mention the complete absence of insect flights, birds, and those furtive movements
in the bush that we are accustomed to during forest walks in our time. A thicket, by the way,
was also nonexistent, since even complex plant life had not yet evolved. So not only no tall
plants, but not even shrubs and blades of grass! Nothing... I tell you nothing at all.
The only life forms were simple and small, living in a kind of ocean slime filled with
filaments of cyanobacteria that struggled to colonize even the moist soils near the beaches.
Because of this, the oxygen in the atmosphere was barely a hundredth of what we breathe today.
To walk in this primitive world, we would have needed oxygen tanks like those on Mars.
At that time, oceans covered 80 percent of the surface, while the land was concentrated
on Rodinia, the supercontinent that was fragmenting into an archipelago of large islands,
all clustered around the equatorial belt. In the mists of time, in short, the world
appeared as a desert whose coasts were battered by storms that shattered volcanic rocks, giving rise
to the first sedimentary layers and sandstones. The day lasted only 18 hours because the Earth
rotated faster than it does today, and the ever-receding Moon was only 350,000
km from our planet, compared to 384,000 km today; this was the cause of accentuated tidal effects.
The spark of life was confined to the oceans in the form of greenish algae,
and an alien explorer who ventured to our planet in that remote era would probably have come away
listing Earth among the barren, uninhabited worlds unworthy of any mention in his logbook.
There is little evidence of significant climate variability during this period. And if there was,
it did not depend on the brightness of the sun, for despite the fact that the sun was 10 percent
less bright than it is today, there is no evidence that Earth's climate was significantly colder. In
fact, the planet was probably a little warmer. In short, at first glance, the Earth seemed to
be in perpetual stasis. Nothing was changing, it was being born
and growing, and everything was decaying. As mentioned earlier, the oxygen in the atmosphere
was only a small fraction of what we breathe today, and even much of the world's oceans were
completely devoid of oxygen, making the seas look more and more like inhospitable expanses of water,
rich in iron or toxic hydrogen sulfide (the foul-smelling gas released by rotten eggs).
The first single-celled organisms, the eukaryotes, had been forming for some time,
but then the pace of evolution seemed to stop as if nature did not quite know which way to go.
There was no freezing or warming, and everything was stale, sterile and unfit for survival.
But before and after this very quiet period, a little bit of everything had happened... At that
time, long ago, 2.5 billion years ago, the Earth had been blessed with the miracle of life with the
formation of cyanobacteria: microscopic "algae" that produce energy by releasing oxygen as waste.
This allowed the atmosphere to be enriched with oxygen, forming a barrier against harmful
radiation and allowing the evolution of new organisms capable of living in its presence.
Among these were the heterotrophs, bacteria unable to produce their own
food and thus forced to become "hunters," which later gave rise to the animal kingdom.
Autotrophic forms instead led to the emergence of the plant kingdom.
Quite a revolution, don't you think? And that's as far as the past goes...but
even as soon as the "quiet" period ended, amazing things happened...in
fact, the Cambrian, or Renaissance, period began...when, in a very short time, the Earth went
from being populated by immobile, single-celled organisms to harboring the sophisticated,
bizarre, and complex life forms that have since evolved into the ones we see today.
And amid these revolutions, nothing. Nothing for a billion years!
All this led biologist Roger Buick, in a 1995 publication, to paraphrase Winston Churchill's
famous line about the Battle of Britain: "Never in the field of human conflict was
so much owed by so many to so few... To define this unchanging period,
Buick instead wrote: "Never in the history of the earth has so little happened for so long.
A poetic license that would soon inspire the late paleontologist Martin Brasier to coin the immortal
phrase "boring billion" to describe the same period. A definition that, from that moment on,
would become firmly entrenched in the imagination of all geoscientists.
But what could have made a whole billion years so seemingly "boring"?
Of course, many theories have arisen to explain the very long period of "no change".
Most experts point to stasis in the tectonic movement of the Earth's crust. This sounds
like a complicated concept... but it's not. In fact, it turns out to be quite
logical when you consider that it is the incessant movement of tectonic plates that
constantly reconfigures the surface of our planet, as if in a slow-motion dance.
Collisions between continents thicken the crust and create mountains like the Himalayas,
which continue to rise into the sky. And if for some reason, tectonics suddenly
slows down, that means there will be a pause in the formation of mountain ranges as well.
We have said it before: the continent of Rodinia was completely flat, with no rising
mountain ranges, and this led to another extreme consequence during the boring billion years.
If there were no more mountains to erode, the rivers could not bring into the oceans
all those elements - first and foremost phosphorus - that are indispensable for
the emergence and strengthening of life! In short, to put it bluntly...
evolution came to a halt "by starvation"! But not only that... a reduced number of
organisms also led to another consequence: a sharp decrease of oxygen in the atmosphere,
which continued throughout the boring billion. In short, the oceans were rotting and gasping,
and the few remaining microorganisms could not produce the amount of oxygen they had previously.
But another factor may also have played a role...
Apparently, recent studies have determined that about 1.2 billion years ago,
the Earth's magnetic field underwent a drastic change and significant weakening.
We now know that the Earth's magnetic field is generated by our planet's core.
A true shield, it protects the living from cosmic radiation and other particles.
But it is still affected by the sometimes capricious weather in space.
Rocks that have preserved the history of the Earth's magnetic field suggest that it has been
active throughout most of our planet's history, and without major changes in its intensity.
The only exception: at the end of the Precambrian, right around the same time as the boring billions
and reducing life in the oceans! A bit too perfect a coincidence - doesn't it seem so?
In short, about a billion years ago, the Earth would have gone from having a "strong" magnetic
field with two opposite poles at the north and south of the planet to having a "weak" magnetic
field that fluctuated in intensity and direction between different poles, before returning to
"normal" at the end of the boring billion! Could it be, then, that the decline of life
on our planet could also have been facilitated by the increase in ultraviolet radiation caused
by the weakening of the magnetic field? In fact, the magnetosphere created by
the Earth's magnetic field played an essential role in the development and maintenance of life
on Earth by deflecting energetic particles from the solar wind and cosmic rays. This has allowed
Earth's atmosphere to be maintained over time, unlike, for example, Mars, where the lack of a
strong magnetic field has allowed the solar wind to literally blow away that planet's atmosphere.
Once the magnetic field was restored, Earth's entire ecosystem resumed functioning.
Life, initially weakened by cosmic rays, began to proliferate, tectonics kicked back into gear,
providing proper food for the oceans, and marine organisms resumed producing
the amount of oxygen that would soon (sort of) lead Earth into the Cambrian explosion of life.
Guys, I really hope you didn't get bored!