The young Sun was about 30 percent dimmer, yet early Earth still had liquid water

science & techWikipediac. 4 billion years ago

The young Sun was about 30 percent dimmer, yet early Earth still had liquid water

the gist

Our Sun was only about 70 percent as bright when Earth was young, which by simple physics should have left the whole planet frozen solid. Yet evidence shows early Earth had liquid water and supported life. The leading explanation is carbon dioxide: the early atmosphere likely held far more of it than today, and its greenhouse warming could have offset the missing sunlight. Other proposals include a darker, less reflective planet and effects from the young Sun's activity, and researchers often combine these ideas. Carl Sagan and George Mullen first raised the puzzle in 1972, and it remains a classic problem in planetary science.

how it works

Stars brighten as they age because fusion in their cores slowly raises their output. A young Sun delivering roughly 70 percent of today's energy would leave Earth's surface far below freezing without help. Greenhouse gases trap outgoing heat, so higher carbon dioxide levels can warm the surface enough to keep oceans liquid.

so what

It shows that a planet's temperature depends on its atmosphere as much as on its star. Solving it helps scientists judge how early planets stay warm enough for oceans, and whether other worlds could have had them.

Hampi was once one of the world's largest cities, until its Vijayanagara capital was destroyed in 1565

the gist

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.

how it works

The city was built around a fortified core with temples, markets and water structures along the river, supplied by an extensive network of roads and waterworks. When the empire fell, the city was not rebuilt, so its stone monuments were left standing.

so what

Hampi shows how quickly a great city can vanish after a military defeat, and how a ruined capital can remain sacred. Its ruins give historians a view of medieval South Asia that few other sites can match.

fun fact

The name Hampi comes from Pampa, an old name for the Tungabhadra River.

From Wikipedia, the free encyclopedia · text CC BY-SA 4.0

Image: Wikimedia Commons

source: Wikipedia ↗

2 min

politicsshortCNA2:01

False allegations about Singapore’s hand in Indonesia’s markets and a made-up meeting

from CNA

CNA Verify has found close to 400 posts pushing falsehoods tying Singapore to Indonesia’s stock market rout and to a secret meeting that never took place. Together, they drew nearly 12 million views, and some were circulated by accounts that appeared to be working in concert, across multiple social media platforms.

Here’s how the disinformation campaign targeting Singapore was uncovered.

on YouTube: CNA ↗