The moon is more than Earth’s natural satellite, having impacted its every aspect, from origin of life to climate change
On July 14, the Indian Space Research Organisation successfully launched Chandrayaan-3, India’s third spacecraft to the moon (Photograph courtesy: ISRO)_ Even though the primary objective of such missions might not be looking into the origin of life, it could find something that is very important,” says Jonti Horner, professor of astrophysics at US’ University of Southern Queensland, referring to Chandrayaan-3.
On July 14, the Indian Space Research Organisation successfully launched India’s third trip to the moon. The spacecraft seeks to land a rover in August and study seismicity and thermal properties of the lunar surface.
Since the 1960s, when Earth’s fascination with its nearest celestial neighbour was at its peak, countries have launched over 110 missions to study the moon.
The attempts have tremendously improved our understanding of not just the moon but also Earth, as well as origin and evolution of life. Evidence suggests the moon had a critical part in seeding and shaping life, and it still does.
“It has definitely had an impact on Earth. Our planet would have looked very different without it. We may have had different organisms with different behaviour, and maybe, humans would not have existed,” David Waltham, professor of geophysics at Royal Holloway, University of London, tells Down To Earth (DTE).
In a cataclysmic event some 60-175 million years after the birth of the solar system 4.5 billion years ago, a Mars-sized planet called Theia collided with Earth. Debris from this event aggregated to form the moon.
This event likely changed Earth. The most immediate impact was in the planet’s composition. On Earth, heavier elements settle in the core and the lighter ones stay concentrated in the crust.
“The collision with Theia likely transported some of the lighter elements like water to the moon. If Earth had more water, then everything would be ocean and we would not have continents,” says Horner.
Next came tides. Some 3.2 billion years ago, the moon was about 70 per cent closer to Earth. The proximity meant stronger and more frequent tides. It is believed that organic molecules delivered by meteorites and comets reacted with each other to form complex molecules, eventually forming nucleic acids such as DNA or RNA, allowing life to take off.
Tides played an important part in facilitating this reaction. During a high tide, coastal areas are underwater, and at low tide, they are dry. Horner explains that this changing environment catalyses complex reactions, facilitating the simple molecules to convert into complex ones. Tides also likely helped ancient marine organisms move to land, after life originated in coastal areas, he adds.
Due to tides, the duration of one Earth day also got extended. Some 1.4 billion years ago, one day lasted 18 hours and 41 minutes. This is due to the tug of war between Earth and the moon.
Both Earth and the moon exert a pull on the oceans. The friction between the seabed and the moving ocean leads to a loss of energy, which ultimately slows the planet.
The moon is drifting away from Earth by 3.8 cm per year, which is roughly the same as fingernail growth. If this rate continues, Earth could lose its natural satellite once it becomes free of the planet’s gravitational pull in about 15 billion years, estimate scientists.
But in about six billion years, the Sun would have run out of fuel, causing it to puff up and destroy Earth and the moon. So a moon free of Earth’s pull is an unlikely scenario.
Still, Earth might start seeing the impacts of a receding moon in 2-3 billion years, Waltham says. As Earth’s rotation slows, its axis will become unstable and it would start wobbling, which would create strong seasons followed by no seasons. “That would play havoc. Organisms would have to evolve to adapt to that,” he says.
Organisms do sync their activities—from migration to navigation to reproduction—with the moon. Researchers have recorded how corals time their reproduction depending on the phases of the moon.
Plants, too, can detect moonlight and the different phases of the moon. Ephedra foeminea, a plant used in Arab medicine, produces a sugary substance that shines in moonlight, attracting insects that aid pollination.
The moon also exerts influence on the climate. Over 18 and half years, the moon’s orbital tilt relative to Earth’s equatorial plane increases or decreases by 5.1 degrees (°). This is the lunar nodal cycle.
When the lunar orbit is aligned with Earth’s equator, the tides are stronger due to higher gravitational forces and when it is tilted away from the equator, the tides are weaker.
“Tides play a very important role in mixing and circulation of the ocean,” Manoj Joshi from the School of Environmental Sciences at UK’s University of East Anglia, tells DTE.
The ocean temperature steadily reduces as we go deeper. The average global sea surface temperature is 16°C, and the deep ocean is only 4°C.
“When tides are strong, there is mixing between upper and lower layers of water, eventually cooling down the surface water temperature. The atmosphere then reacts to the ocean cooling,” Joshi explains.
Joshi and his colleagues used computer modelling to study the contribution of the lunar nodal cycle to global temperatures. They found that world will see a global cooling due to the lunar nodal cycle in the mid-2020s and warming in the early 2030s. Further, sea levels also fluctuate with tides. NASA says daily tides are intensified in one-half of the lunar nodal cycle.
During this period, high tides get higher, and low tides get lower. In the mid-2030s, every US coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change, warns a 2021 NASA study. Perhaps, one of the moon missions will also provide keys to tackle climate change.
This was first published in the 1-15 August, 2023 edition of Down To Earth
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