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In a study conducted in 117 countries, researchers have found that the world is experiencing the most dramatic reduction in the seismic noise (the hum of vibrations in the planet's crust) in recorded history due to global COVID-19 lockdowns.

Measured by instruments called seismometers, seismic noise is caused by vibrations within the Earth, which travel like waves and the waves can be triggered by earthquakes, volcanoes, and bombs - but also by daily human activity like travel and industry.

This quiet period was likely caused by the total global effect of social distancing measures, closure of services and industry, and drops in tourism and travel, the study published in the journal Science, reported.

The new research, led by the Royal Observatory of Belgium and five other institutions around the world including Imperial College London (ICL), showed that the dampening of 'seismic noise' caused by humans was more pronounced in more densely populated areas.

"Our study uniquely highlights just how much human activities impact the solid Earth, and could let us see more clearly than ever what differentiates human and natural noise," said study co-author Stephen Hicks from ICL in the UK.

For the findings, the research team looked at seismic data from a global network of 268 seismic stations in 117 countries and found significant noise reductions compared to before any lockdown at 185 of those stations.

Researchers tracked the 'wave' of quietening between March and May as worldwide lockdown measures took hold.

The largest drops in vibrations were seen in the most densely populated areas, like Singapore and New York City, but drops were also seen in remote areas like Germany's the Black Forest and Rundu in Namibia.

Citizen-owned seismometers, which tend to measure more localised noise, noted large drops around universities and schools around Cornwall, UK and Boston, US - a drop in noise 20 per cent larger than seen during school holidays.

The findings showed that countries like Barbados, where lockdown coincided with the tourist season, saw a 50 per cent decrease in noise.

"The changes have also given us the opportunity to listen in to the Earth's natural vibrations without the distortions of human input," the study authors wrote.

Earlier in April, a study published in the journal Nature, reported at least a 30 per cent reduction in that amount of ambient human noise since lockdown began in Belgium.

US dictionary Merriam-Webster will update the meaning of the word "racism" after being contacted by a Missouri black woman, who claimed the current definition fell short of including the systematic oppression of people of colour, according to media reports.

"A revision to the entry for racism is now being drafted to be added to the dictionary soon, and we are also planning to revise the entries of other words that are related to racism or have racial connotations," according to a statement of the 189-year-old dictionary shared by Kennedy Mitchum, a recent graduate of Drake University in Iowa, on her Facebook.

Mitchum, 22, emailed the dictionary last month, following the death of African American George Floyd in the custody of four Minneapolis police officers, Xinhua news agency reported.

"I kept having to tell them that definition is not representative of what is actually happening in the world," Mitchum told CNN. "The way that racism occurs in real life is not just prejudice, it's the systemic racism that is happening for a lot of black Americans."

Merriam-Webster's first definition of racism is "a belief that race is the primary determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race."

"It's not just disliking someone because of their race," Mitchum wrote in a Facebook post on Friday. "This current fight we are in is evidence of that, lives are at stake because of the systems of oppression that go hand-in-hand with racism."

New Delhi, Jul 19: Three of the 10 most valued companies added a total of Rs 98,622.89 crore to their market valuation last week, led by stellar gains in IT major Infosys.

Seven companies from the coveted list witnessed a decline in their market valuation last week, but their cumulative loss of Rs 37,701.1 crore was less than the total gain made by three firms -- Reliance Industries Limited, Hindustan Unilever Limited and Infosys.

The market capitalisation of Infosys zoomed Rs 52,046.87 crore to Rs 3,85,027.58 crore. Shares of Infosys had rallied over 9 per cent on Thursday after the company posted a stronger-than-expected 12.4 per cent rise in the first quarter consolidated net profit.

Hindustan Unilever Limited added Rs 25,751.07 crore in its market valuation which stood at Rs 5,48,232.26 crore at close on Friday. Reliance Industries' m-cap jumped Rs 20,824.95 crore to Rs 12,11,682.08 crore.

In contrast, HDFC's valuation plunged Rs 13,920.21 crore to Rs 3,13,269.70 crore and that of Tata Consultancy Services (TCS) declined Rs 7,617.34 crore to Rs 8,26,031.21 crore.

The valuation of ICICI Bank tumbled Rs 4,205.71 crore to Rs 2,29,156.24 crore and that of Kotak Mahindra Bank by Rs 4,175.28 crore to Rs 2,62,864.37 crore.

Bharti Airtel's m-cap dipped Rs 4,009.83 crore to Rs 3,09,521.05 crore and HDFC Bank's by Rs 3,403.97 crore to Rs 6,03,463.97 crore.

The valuation of ITC declined by Rs 368.76 crore to Rs 2,38,469.29 crore.

In the ranking of top-10 firms, RIL was at the number one rank followed by TCS, HDFC Bank, HUL, Infosys, HDFC, Bharti Airtel, Kotak Mahindra Bank, ITC and ICICI Bank.

During the last week, the 30-share BSE index advanced 425.81 points or 1.16 per cent.