‘The Hindu’ News : Science For All 12 June 2024

Science For All

12 June 2024

This newsletter from The Hindu’s science writers takes the jargon out and puts the fun in science! It is written and curated this week by Arkatapa Basu.

Did an interstellar cloud cause the last ice age?
The last time the earth experienced an ice age was approximately 2.6 million years ago and lasted 450,000 years. Scientists have various explanations for why the planet became cooler this time, including the planet’s tilt and rotation, shifting plate tectonics, volcanic eruptions, and carbon dioxide levels in the atmosphere.

However, new evidence published in Nature Astronomy this week points to a different culprit altogether. The new study suggests the Solar System entered a dense interstellar cloud about 2 million years ago, shifting the earth’s climate.

The report suggests the Sun’s position in the galaxy might have a significant influence on the earth’s history, an idea that could reshape our understanding of the relationship between cosmic events and terrestrial life.

Stars, including our Sun, move through the galaxy, encountering various interstellar environments. The Sun emits a continuous flow of charged particles called the solar wind, which protects the solar system from harmful cosmic radiation. This protective bubble, thought to be shaped like a croissant, is called the heliosphere. It extends well beyond Pluto, and is one of the reasons life as we know it exists on the earth.

According to astrophysicist and the lead author of the study Merav Opher, almost 2 million years ago, a cold cloud had interrupted the bubble, causing the earth and some of the other planets to be stripped of the protective influence of the heliosphere.

Dr. Opher and her collaborators used sophisticated computer models to trace the Sun’s position at this time. Their simulations showed the solar system passed through a particularly dense section of cold cloud full of hydrogen atoms, called the Local Lynx of Cold Cloud, which was part of the bigger Local Ribbon of Cold Clouds.

This event would have pushed the heliosphere inward, leaving the earth exposed to the interstellar medium’s gas and dust, including elements from supernovae such as iron and plutonium.

The study aligns with geological evidence of increased iron-60 and plutonium-244 isotopes in ocean sediments, lunar samples, Antarctic snow, and ice cores from that epoch. The findings also correspond with a cooling period in the earth’s climate records, suggesting the cosmic encounter influenced global temperatures, with significant, but not entirely understood, effects on our planet’s atmosphere and climate.

The duration of the earth’s exposure to the interstellar medium could have ranged from a few centuries to a million years depending on the cloud’s size. Once the solar system moved past the cloud, the heliosphere would have re-expanded to encompass all the planets, resuming its protective role. The full impact of this exposure is not yet clear; Dr. Opher’s team is currently investigating its potential effects on radiation levels on the earth and on the atmosphere and the climate.

The researchers are also looking further into the past to trace the Sun’s path 7 million years ago, and possibly even further back, for signs of cosmic interference in the earth’s planetary history.

From the Science pages
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China’s spacecraft carrying rocks from the far side of the moon leaves the lunar surface
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Study shows elephants might call each other by name
‘Green-beard’ genes could explain how altruism arose in nature
Wild horse species returns to Kazakh steppes
Two antlion species found for first time in India, Thailand
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