Hello Nature readers, would you like to get this Briefing in your inbox free every day? Sign up here

True-colour satellite image of Earth, showing Australia and surrounding ocean.

Oceanic crust from the Panorama district in the Pilbara Craton of Western Australia is a time capsule of early Earth.Planet Observer/Universal Images Group via Getty

Early Earth might have been a water world

Early Earth might have been covered with ocean and almost devoid of land. Researchers examined the ratio of oxygen isotopes in a 3.2-billion-year-old slab of the planet’s crust that is exposed in Western Australia. High levels of oxygen-18 in the oldest rock suggest that continents (which absorb that isotope) might not have emerged until between 3 billion and 2.5 billion years ago.

The Guardian | 5 min read

Reference: Nature Geoscience paper

COVID-19 coronavirus outbreak

Officials take the temperatures of people standing in queues, some wearing face masks.

Authorities monitor people for coronavirus symptoms at Kraków airport in Poland.Credit: Beata Zawrzel/NurPhoto/Getty

Global infections pass 90,000

• The number of people worldwide who have been infected with coronavirus that causes COVID-19 has passed 90,000. More than 3,000 people have died since the outbreak began in December. The vast majority of cases have occurred in China, but around 60 other places have reported infections. South Korea, Italy and Iran are fighting the largest outbreaks outside China. (Nature | Continuously updated)

• The World Health Organization (WHO) has raised the global alert for COVID-19 to ‘very high’ — the highest possible level short of calling it a pandemic. The assessment is based on the continued increase in cases and affected locations, and the difficulties that regions such as Iran and Italy are facing in containing the spread. “We still have a chance of containing this virus, if robust action is taken to detect cases early, isolate and care for patients and trace contacts,” said Tedros Adhanom Ghebreyesus, director-general of the WHO. (Nature | Continuously updated)

• The United States is falling behind on diagnosing coronavirus infections after the Centers for Disease Control and Prevention (CDC) struggled to mass-produce a working test. Flaws in the CDC’s kit were discovered only after hundreds had been shipped to state laboratories last month. (The New York Times)

Read the latest coronavirus news, continuously updated on Nature.

Notable quotable

“China has rolled out perhaps the most ambitious, agile, and aggressive disease containment effort in history.”

China’s response to COVID-19 has been effective, says a WHO report released on 28 February. (Science)

Reference: WHO report

Features & opinion

What we learnt from retracting a paper

“Someone I admire retracted a very important paper when I was a young scientist,” says Nobel-prizewinning chemist Frances Arnold, who retracted a paper in January. “I wanted to pay that lesson forward.” Arnold and three other senior scientists share what they learnt from the experience of retracting flawed papers.

Nature Index | 4 min read

Open your lab to art

When ecologist Matthias Rillig welcomed artist Karine Bonneval into his lab, he saw some benefits he had not expected. In the end, a new research question was born, which resulted in a paper listing Bonneval as a co-author. Rillig offers his advice for scientists on how to make the most of an artist-in-residence.

Nature | 8 min read

Reference: Soil Systems paper

News & views

One gene sets the stage for toxoplasmosis

Around one-third of the global human population is infected with the single-celled organism Toxoplasma gondii, which in some cases causes the incurable disease toxoplasmosis. Researchers have found a single gene that controls the conversion of the parasite into a form that chronically infects the human brain. Targeting the gene, BFD1, shows real potential for making progress in the development of drugs or vaccines, writes biochemist Eva-Maria Frickel.

Nature | 6 min read

Reference: Cell paper

Image of the week

In a 340-litre aquarium, researchers smashed vortices of coloured fluid together to study turbulence. They discovered a cascading cycle of propagating, ever-smaller vortices — “a Russian nesting doll of disorder”. (Harvard John A. Paulson School of Engineering and Applied Sciences press release)

Two vortex cannons fire in an aquarium to produce colliding vortices

Video courtesy of Harvard SEAS

Reference: Science Advances paper (Video courtesy of Harvard SEAS)

Quote of the day

“The beauty of science is that all the important things are unpredictable. The optimistic view in me is that nature is designed to make the universe as interesting as possible.”

Physicist Freeman Dyson, who died on Friday at the age of 96, spoke to physicist Katie Mack last year about the end of the Universe. (The New York Times)