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466 million years ago, the impact of asteroids was very important. But despite what you think, it does help life on Earth is fruitful and multiplies.
And that's because the impact of the asteroid was not on Earth. It was hundreds of millions of kilometers away, in the inner asteroid belt.
Wait what? How would that affect us here?
A new document written by a team of scientists points the accusing finger on … the dust. A lot of this, burst outward when two large asteroids collided. This dust went to the Earth, blocked a significant fraction of the sunlight, triggered an ice age, which created stress for the marine environment, causing a break in evolutionary diversity.
OK, hang on tight. There are a few things going on here, so we have to step back and see how it all fits together.
Palaeontologists have known for some time that about 465 million years ago, at the end of the Ordovician period, the marine life of invertebrates on Earth was highly diversified. Relatively sharply (over a few million years), life forms that had evolved and flourished from the Cambrian period a few tens of millions of years ago began to disappear and new varieties of animals have emerged.
This is what is called the great Ordovician Biodiversity Event (or GOBE). It has also been known for some time that the level of oxygen in the oceans has increased at about the same time. It has also been shown that the sea level also fell overall at that time. These two phenomena indicate a great ice age: when the water freezes, the level of the oceans decreases and colder water can contain more dissolved gases. This type of stress on an environment can trigger sudden biodiversity when competition increases.
But what caused the glaciation? On short time scales (like tens or hundreds of thousands of years), they are caused by changes in the shape of Earth's orbit, called Milankovitch cycles. On much longer time scales, they are generally related to tectonic events, massive climatic changes due to mountain uplift or the displacement of continental plates to open or close marine passages, or even extensive volcanic eruptions. Extending over millions of years. These can cause enormous global changes in the air and water circulation, causing glacial periods. There have been three centuries of glaciation over the past 500 million years – we are technically in the same period, in an "interglacial period" between heavy episodes of glaciation, although I am not particularly worried about the start of glaciers. again.
Around the same time in the Ordovician, a huge asteroid about 150 kilometers in diameter was broken. This asteroid was in the asteroid belt between Mars and Jupiter and most likely suffered a massive collision with another big asteroid. This asteroid was large enough that after its formation and it was still melting, heavier elements, such as iron, sagged towards the center and lighter, upward. This has created minerals such as olivine and pyroxene, which are common in coats and larger worlds, as well as chromite, which could come from deeper and deeper.
We know this because many stony meteorites falling on Earth were once partially or completely melted and do not contain much iron. We call these L chondrites (L for low iron content), and those of this dissolution event still constitute more than a third of all the meteorites that hit our planet, even today.
The sedimentary rocks of the Ordovician show an increase in the number of L chondrites (which also contain the same minerals as those mentioned above) at the time of the GOBE. Scientists have tried to connect the two. Craters built at this time have been found, but they tend to be a little small (10 km); big by human standards, but far too small to have triggered an ice age. In addition, it is impossible to obtain exact dates for the impacts. It is therefore difficult to link them directly.
And this is where the new study comes in. Instead of asking whether there were significant impacts that triggered the diversification of the Ordovician, they wondered whether some other The appearance of the breaking of the asteroid was the culprit. Like, say, dust.
During an asteroid collision, you get a few big pieces, lots of medium sized pieces and countless smaller particles to microscopic sizes – that is, dust. Scientists visited a sedimentary rock wall exposed in southern Sweden and another near St. Petersburg, Russia. They examined the layer corresponding to the Ordovician and examined some samples. What they found is, to say the least, intriguing.
They found very many tiny micrometeorites in the layers, many with chromite. Neon bubbles are trapped in the chromite. While in space, tiny subatomic particles circulating around you, called cosmic rays, can zap neon, altering its atomic structure. The more they stay in space, the more neon lights are changed.
Scientists have discovered that the time of exposure to cosmic rays in chromite was all the longer as chromite was discovered earlier (closer to the surface). This makes sense if a single event had projected many tiny rocks into space, and some of them quickly reached Earth (about 100,000 years after the event), while some lasted longer ( over a million years). Objects that hit us right away have the shortest cosmic ray exposure time, and those who hit later have spent more time in space.
It is therefore the dust and tiny grains (smaller than the width of a human hair) of the rock coming from the breaking of the asteroid! Here is the really astonishing thing: the amount of chromite grains deposited in these layers indicates that the speed at which this material fell on Earth was 100 to 1000 times the rate we see today.
Hum C is a lot. On average, about 100 tons of meteorites, most of them very small, burn daily in our atmosphere. Shortly after the breakup of the asteroid 466 million years ago, this rate was 10,000 to 100,000 tons per day!
It would be a great job to explain what happened next. After the asteroid collision, a lot of dust was generated. Over time, a strange effect of sunlight striking the grains (called Poynting-Robertson effect) robs them of orbital energy and drops them closer to the sun. It does not take them long to reach the Earth's orbit, where they have spilled into our atmosphere. This huge cloud of opaque material dropped incoming sunlight in fractions, enough to trigger an ice age. After that, you know the story. Incidentally, the chromite leap observed in the sediment layers occurs just before the sea level drops. Who corresponds; dust fell and glaciation began shortly thereafter, reducing levels when the water froze.
I will note that they used several methods to examine the amount of extraterrestrial debris that went down. Another one they used, for example, was measuring the 3It – an isotope of helium – in sediments. 3It comes from the Sun by the solar wind and permeates the materials in space. The more the cosmic ray is measured, the longer a meteorite is, and the longer it goes into space. They found that levels rose quite abruptly about 50,000 years after the breakup of the asteroid, which corresponds well to cosmic ray measurements.
This is incredible. I tend to think that asteroids have an effect on the Earth when they hit us violently, causing huge explosions, tsunamis, fire storms, and then possibly smother the air with enough dust to provoke a "nuclear winter" (not the best name for it because no nuclear weapon is involved, but the effect is the same). In this case, the impact occurred hundreds of millions of kilometers away, but even had a huge impact on our planet. An ice age is a big deal.
As usual, a warning: This is a convincing assumption, supported by good evidence. But it is not confirmed yet and it will take a lot more work. We must remain skeptical, as do scientists, even if they are looking for more data that can support or refute this idea.
A last note. What happened to the asteroid itself? It is unlikely that a beast of such magnitude has completely disintegrated under the effect of an impact. It is therefore likely that there are still pieces left. From what I've discovered, the Flora and Gaspra asteroids could be the biggest pieces left over. They do decent work by matching the spectral characteristics of L chondrites, but that is not certain. It would be very interesting to be able to commission a mission to take samples of these asteroids and send them back to Earth so that we can examine them in the laboratory. One day.
The space seems so far away. But it affects every aspect of our lives. That's also, literally, why we are here.
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