Categories
Earth Finally

We may finally know what life on Earth breathed before there was oxygen – Live Science

La Brava microbial mats.

La Brava microbial mats.

Billions of years ago, long before oxygen was readily available, the notorious poison arsenic could have been the compound that breathed new life into our planet.

In Chile’s Atacama Desert, in a place called Laguna La Brava, scientists have been studying a purple ribbon of photosynthetic microbes living in a hypersaline lake that’s permanently free of oxygen.

“I have been working with microbial mats for about 35 years or so,” says geoscientist Pieter Visscher from the University of Connecticut.

“This is the only system on Earth where I could find a microbial mat that worked absolutely in the absence of oxygen.”

Microbial mats, which fossilize into stromatolites, have been abundant on Earth for at least 3.5 billion years, and yet for the first billion years of their existence, there was no oxygen for photosynthesis.

How these life forms survived in such extreme conditions is still unknown, but examining stromatolites and extremophiles living today, researchers have figured out a handful of possibilities. 

While iron, sulphur, and hydrogen have long been proposed as possible replacements for oxygen, it wasn’t until the discovery of ‘arsenotrophy‘ in California’s hypersaline Searles Lake and Mono Lake that arsenic also became a contender.

Since then, stromatolites from the Tumbiana Formation in Western Australia have revealed that trapping light and arsenic was once a valid mode of photosynthesis in the Precambrian. The same couldn’t be said of iron or sulphur.

Just last year, researchers discovered an abundant life form in the Pacific Ocean that also breathes arsenic. 

Even the La Brava life forms closely resemble a purple sulphur bacterium called Ectothiorhodospira sp., which was recently found in an arsenic-rich lake in Nevada and which appears to photosynthesize by oxidising the compound arsenite into a different form -arsenate.

While more research needs to verify whether the La Brava microbes also metabolize arsenite, initial research found the rushing water surrounding these mats is heavily laden with hydrogen sulphide and arsenic.

If the authors are right and the La Brava microbes are indeed ‘breathing’ arsenic, these life forms would be the first to do so in a permanently and completely oxygen-free microbial mat, similar to what we would expect in Precambrian environments.

As such, its mats are a great model for understanding some of the possible earliest life forms on our planet. 

While genomic research suggests the La Brava mats have the tools to metabolize arsenic and sulphur, the authors say its arsenate reduction appears to be more effective than its sulfate reduction.

Regardless, they say there’s strong evidence that both pathways exist, and these would have been enough to support extensive microbial mats in the early days of life on Earth.

If the team is right, then we might need to expand our search for life forms elsewhere.

“In looking for evidence of life on Mars, [scientists] will be looking at iron and probably they should be looking at arsenic also,” says Visscher.

It really is so much more than just a poison.

The study was published in Communications Earth and Environment

This article was originally published by ScienceAlert. Read the original article here.

Read More

Categories
'Staggering' Earth

Earth Lost a ‘Staggering’ 28 Trillion Tonnes of Ice in Just 23 Years – ScienceAlert

  • A group of UK scientists found that a “staggering” 28 trillion tonnes of ice has disappeared from the surface of the Earth since 1994.
  • By analyzing satellite surveys, the group found that melting glaciers and ice sheets could cause sea levels to rise dramatically, possibly reaching a meter (3 feet) by the end of the century.
  • The findings match the worst-case-scenario predictions outlined by the United Nation’s Intergovernmental Panel on Climate Change (IPCC), the scientists have confirmed.
  • They come a week after researchers at Ohio State University discovered that Greenland’s ice sheet — the world’s second-largest ice body — may have passed a point of no return.

A “staggering” 28 trillion tonnes of ice has disappeared from the surface of the Earth since 1994, a group of UK scientists has found.

Scientists from Leeds and Edinburgh universities and University College London analyzed satellite surveys of glaciers, mountains, and ice sheets between 1994 and 2017 to identify the impact of global warming. Their review paper was published in the journal Cryosphere Discussions.

Describing the ice loss as “staggering,” the group found that melting glaciers and ice sheets could cause sea levels to rise dramatically, possibly reaching a meter (3 feet) by the end of the century. Advertisement


“To put that in context, every centimeter of sea-level rise means about a million people will be displaced from their low-lying homelands,” Professor Andy Shepherd, director of Leeds University’s Center for Polar Observation and Modelling, told the Guardian.

The dramatic loss of ice could have other severe consequences, including major disruption to the biological health of Arctic and Antarctic waters and reducing the planet’s ability to reflect solar radiation back into space.

The findings match the worst-case-scenario predictions outlined by the United Nation’s Intergovernmental Panel on Climate Change (IPCC), the scientists have confirmed.

Advertisement


“In the past researchers have studied individual areas – such as the Antarctic or Greenland – where ice is melting. But this is the first time anyone has looked at all the ice that is disappearing from the entire planet,” said Shepherd, according to the Guardian. “What we have found has stunned us.”

“There can be little doubt that the vast majority of Earth’s ice loss is a direct consequence of climate warming,” the group wrote.The findings come a week after researchers at Ohio State University discovered that Greenland’s ice sheet might have passed a point of no return.Advertisement


According to the researchers, snowfall that replenishes the country’s glaciers each year can no longer keep up with the pace of ice melt, which means that the Greenland ice sheet will continue to lose ice even if global temperatures stop rising.

The Greenland ice sheet is the world’s second-largest ice body.

“What we’ve found is that the ice that’s discharging into the ocean is far surpassing the snow that’s accumulating on the surface of the ice sheet,” Michalea King, lead author and researcher at Ohio State University’s Byrd Polar and Climate Research Center, said in a press release.Advertisement


According to a NASA study, 2010-2019 was the hottest decade ever recorded.

Read More

Categories
degrees Earth

Earth was 130 degrees this week. It will be much hotter one day. – National Geographic

As a heat wave roasted the western United States this week, temperatures in California’s Death Valley soared to a blistering 130 degrees Fahrenheit, marking the hottest temperature measured anywhere on Earth since 1931 and the third hottest day ever recorded on our planet, period.

But Earth has seen warmer days in its past and it will experience them again in the future. During so-called hothouse periods, when the atmosphere was supercharged with greenhouse gases, the planet was much warmer than it is today and the worst heat waves were correspondingly nightmarish. And while human carbon emissions haven’t pushed Earth into a new hothouse state yet, climate change is making heat waves more frequent and severe, meaning Death Valley’s extreme temperatures are unlikely to stand for long. Earth won’t be as scorching and uninhabitable as Venus anytime soon—temperatures there are hot enough to melt lead—but heat that challenges the limits of human tolerance will occur more often as the century wears on, scientists say.

And in the very, very distant future, Earth might actually become like Venus.

The scorching past

It might not feel like it if you live in California or Japan right now, but Earth is currently in what geologists consider an icehouse climate: a period cold enough to support an ice-age cycle, in which large continental ice sheets wax and wane near the poles. (Right now the one in the northern hemisphere has retreated to Greenland.) To get a glimpse of what a much warmer world would look like, we need to go back at least 50 million years to the early Eocene.

“That was sort of the last really warm climate the Earth experienced,” says Jessica Tierney, a paleoclimatologist at the University of Arizona.

Today, Earth’s average temperature hovers around 60 degrees Fahrenheit. During the early Eocene, it was closer to 70 degrees and the world was a different place. The poles were free of ice; the tropical oceans simmered at spa-like temperatures of 95 degrees Fahrenheit. Palm trees and crocodiles hung out in the Arctic. Several million years before that, at the Paleocene-Eocene Thermal Maximum (PETM), things were even warmer.

More extreme hothouse periods lurk in the deeper recesses of geologic time. During the Cretaceous Hot Greenhouse 92 million years ago, global surface temperatures rose to around 85 degrees Fahrenheit and remained hot for millions of years, allowing temperate rainforests to flourish near the South Pole. Some 250 million years ago, the boundary between the Permian and the Triassic period is marked by an extreme global heating event where Earth’s average temperature flirted with 90 degrees Fahrenheit for millions of years, according to a preliminary reconstruction from the Smithsonian Institution.

In that hellish interval, Earth experienced the worst die-off of life in its history. The tropical oceans were like a hot tub. We don’t have daily weather data from the Permian (or any other ancient chapter in Earth’s history), but it’s likely that in the vast, dry interior of the supercontinent Pangea this week’s Death Valley heat wave would have been just another day.

“The warmer these average conditions are, the more often you’ll see really extreme heat events,” Tierney says. On the hottest days during the hottest times, “places like a desert would just be unbelievably hot.”

The warming future

All of Earth’s recent hothouse periods seem to have one thing in common: They were preceded by a massive pulse of greenhouse gases into the atmosphere, whether that was volcanic eruptions spewing carbon dioxide or methane bubbling up from beneath the seabed. Humans are conducting a similar planetary experiment today by burning through enormous reserves of fossil carbon, raising atmospheric carbon dioxide levels at a rate unseen since the extinction of the dinosaurs, 65 million years ago, and perhaps far earlier.

“Usually when we see a rapid change in climate [in the past], it’s driven by similar mechanisms to what we’re doing today,” says MIT earth scientist Kristin Bergmann. “There’s a fairly quick change in the greenhouse gases that warm our planet.”

As in the past, global average temperatures are once again rising quickly. And extremely hot days are also on the uptick, with study after study concluding that recent record-breaking temperatures would have been nearly impossible without our influence.

It’s difficult to forecast exactly how hot Earth might get if we keep jamming carbon into the atmosphere, experts say. As Michael Wehner, an extreme weather researcher at Lawrence Berkeley National Laboratory, put it in an email: “The increase in temperatures of future heat waves depends a lot on how far into the future and how much more carbon dioxide we emit.”

But recent research by Wehner and his colleagues offers a peek into what the heat waves of tomorrow could look like if we don’t curb our carbon emissions at all: By the end of the century, heat waves in California could top out at temperatures about 10 to 14 degrees Fahrenheit higher than they do today.

That once-in-a-century temperature Death Valley saw this week? “I would expect that an event of the same rarity as today’s 130F would be about 140F in that high-emission future,” Wehner says.

A Venus-like fate?

If you’re a nihilist, you might point out that all of this is peanuts compared with what Earth will likely experience in the far future. Planetary scientists have long predicted that as the sun ages and grows brighter, Earth’s surface will eventually heat up to the point where the oceans start to simmer like water on a stove. Water vapor, a potent greenhouse gas, will pour into the atmosphere, triggering a runaway greenhouse effect that, in a billion years, could transform our world into something not unlike our neighbor, Venus. There, beneath a thick, toxic, and sulfurous atmosphere, surface temperatures are close to 900F.

“The assumption has been as the sun continues to brighten, the same thing will happen on Earth,” says North Carolina State university planetary scientist Paul Byrne, adding that billions of years ago, our planetary neighbor might have had an agreeable climate and oceans.

Venus might not have ruined by the sun at all. Recent modeling work suggests that the culprit might have been a series of volcanic paroxysms that caused “biblical releases of CO2 into the atmosphere,” Byrne says. But either scenario—planetary heat death by the sun or by volcanoes—points to a way that events far beyond our control might send Earth’s future climate into a harrowingly hot tailspin.

“Whether it’s going to be exactly 475 degrees Celsius or not I don’t know,” Byrne says, referring to the temperature at Venus’s surface. But if Earth goes through a Venus-like transition, “it will be really, really hot.”

Even if our Blue Marble manages to escape Venus’ fate, there’s no avoiding getting blow-torched in about five billion years. At that time, the sun will expand into a red giant star, subsuming the Earth in a fiery blaze.

“The prevailing view is that the sun will swallow earth,” Byrne says. “We’re getting [expletive deleted].”

Read More

Categories
Earth Venus

See Earth and Venus from Mars in amazing photos from NASA’s Curiosity rover – Space.com

NASA’s Curiosity rover took a break from assessing ancient Martian habitability to gaze up at the Red Planet sky — where it found Earth.

Through the dusty Martian atmosphere, the car-size rover spotted its home planet and Venus about 75 minutes after local sunset on June 5, 2020, the 2,784th sol (Martian day) of Curiosity’s mission. (The rover landed on Aug. 5, 2012.)

“A two-image twilight panorama reveals Earth in one frame and Venus in the other,” officials at NASA’s Jet Propulsion Laboratory in Pasadena, California, which manages Curiosity’s mission, said in a statement. “Both planets appear as mere pinpoints of light, owing to a combination of distance and dust in the air. They would normally look like very bright stars.”

Related: Amazing Mars photos by NASA’s Curiosity rover (latest images) 

Two images of the night sky were combined to show Earth and Venus as seen by the Mast Camera aboard NASA's Curiosity Mars rover on June 5, 2src2src, the 2,784th Martian day, or sol, of the mission. Both planets appear as mere pinpoints of light owing to a combination of distance and dust in the air; they would normally look like bright stars. A feature called Tower Butte is just visible at the bottom of the image, part of the clay-bearing region that Curiosity has been exploring since early 2src19.

Two images of the night sky were combined to show Earth and Venus as seen by the Mast Camera aboard NASA’s Curiosity Mars rover on June 5, 2020, the 2,784th Martian day, or sol, of the mission. Both planets appear as mere pinpoints of light owing to a combination of distance and dust in the air; they would normally look like bright stars.  A feature called Tower Butte is just visible at the bottom of the image, part of the clay-bearing region that Curiosity has been exploring since early 2019. (Image credit: NASA/JPL-Caltech)

To capture the new images, Curiosity used the same instrument it commonly employs to take Martian panoramas, the Mast Camera or Mastcam. And planet-spotting wasn’t the only goal of this skywatching session: mission team members also wanted to look at the Martian twilight brightness. 

On Mars, the planet’s southern hemisphere (where Curiosity is situated, slightly below the equator in a big crater named Gale) is in late spring. The Red Planet takes about 687 Earth days to circle the sun once; a typical day on Mars is about 37 minutes longer than on Earth.

Two images of the night sky were combined to show Earth and Venus as seen by NASA's Curiosity Mars rover on June 5, 2src2src, the mission's 2,784th Martian day, or sol. The planets appear as pinpoints of light owing to a combination of distance and dust in the air. Mars' Tower Butte is visible at bottom.

Two images of the night sky were combined to show Earth and Venus as seen by NASA’s Curiosity Mars rover on June 5, 2020, the mission’s 2,784th Martian day, or sol. The planets appear as pinpoints of light owing to a combination of distance and dust in the air. Mars’ Tower Butte is visible at bottom. (Image credit: NASA/JPL-Caltech)

During the late Martian spring, there is quite a bit of dust suspended in the air. The particles reflect sunlight, brightening the atmosphere and making it harder to spot objects in the sky, said Mastcam co-investigator Mark Lemmon, a senior research scientist at the Space Science Institute in Colorado.

“Even moderately bright stars were not visible when this image of Venus was taken,” Lemmon said in the same statement. “Earth also has bright twilights after some large volcanic eruptions.”

Just visible at the bottom of the images is a rock feature nicknamed Tower Butte. Curiosity is slowly climbing the slopes of Mount Sharp (also known as Aeolis Mons), which rises from Gale’s center, on a quest to understand how water may have shaped habitable environments on Mars more generally. 

NASA’s next Mars rover, Perseverance, is expected to touch down inside the 28-mile-wide (45 kilometers) Jezero Crater on Feb. 18, 2021, to probe ancient habitability in more detail and cache the most promising samples for a future Martian sample return mission. Perseverance’s launch window opens on July 20.

Follow Elizabeth Howell on Twitter @howellspace. Follow us on Twitter @Spacedotcom and on Facebook.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Read More