Connect with us

Science

Geology and genesis – Resource Clips

Published

on


Canadian and Australian rocks offer clues about the origin of life

by Joshua Davies, Professor, Sciences de la Terre et de l’atmosphère, Université du Québec à Montréal and Jesse Reimink, Assistant Professor, Geosciences, Pennsylvania State University | posted with permission of The Conversation | June 17, 2020

The rocks at the surface of modern Earth are broadly divided into two types: felsic and mafic. In general felsic rocks are relatively low in density—for a rock—and light in colour because they are made from whitish minerals rich in silicon and aluminium. Half Dome in California is made of granite, a felsic rock. Mafic rocks, in contrast, are relatively high in density and dark in colour because they contain minerals rich in iron and magnesium. Giant’s Causeway in Northern Ireland is made of basalt, a mafic rock.

The Giant’s Causeway in Northern Ireland is an
unusual rock formation comprising mafic rocks.
(Photo: Bruno Biancardi/Shutterstock)

The difference in density between felsic and mafic rocks means that felsic rocks are more buoyant and therefore sit at higher elevations above the earth’s mantle (the layer inside the earth between the crust and the core). For this reason, felsic rocks make up Earth’s continents whereas the lower-elevation crust under the oceans is mafic.

The mechanisms that separated the rocks at Earth’s surface into these two groups may have also created the environment needed for life to flourish 4.3 million years ago, very early in the history of Earth.

The separation into these two rock types is the result of plate tectonics: where the tectonic plates separate and move apart, the rocks below become depressurized, melt and fill in the gap between them, like the Mid-Atlantic Ridge. The rock that fills the gap between the plates is mafic.

When one plate slides below another, fluids released from the lower plate cause melting in the mantle. These melts have to pass through the upper plate to reach the surface. On their way to the surface, they undergo a series of processes called fractional crystalization, which can change mafic melts into felsic melts.

Establishing timelines

When this separation happened is a matter of great debate in earth sciences because it may allow us to determine when Earth became habitable for life. Many earth scientists believe that the weathering of continental crust may have provided the nutrients for life to thrive. Identifying when the first continents formed indicates when this may have occurred.

Earth scientists also debate whether plate tectonic processes in the past were the same as those occurring today, and whether they were even needed to form continental crust in the past. The first continental crust may have been formed through the interaction of oceanic crust and mantle plumes of heat coming from the earth’s core. Another theory suggests that continental crust formed through meteorite bombardment.

Canadian and Australian rocks offer clues about the origin of life

The former Jack Hills iron ore mine in a Western Australian
region with the world’s oldest known rocks.
(Photo: SRK Consulting)

The exact mechanism is important for understanding the history and evolution of Earth, and may help understand the processes that could be occurring on other planets.

Reviewing the records

Our recent study looked at the oldest geological material on Earth. The results suggest that Earth was already separating into these two rock types by 4.3 billion years ago—effectively since the beginning of Earth’s geological record. Our data also gave intriguing insights into the tectonic processes that may have been occurring at that time.

The origin of continental crust is debated in part because the further back in time you go, the fewer rocks there are to study. Samples from the Acasta Gneiss Complex in the Northwest Territories were found to be about four billion years old—the oldest known rocks on Earth. These Acasta Gneiss rocks are felsic and composed of tonalite-trondhjemite-granodiorite.

There are very few older samples from Earth, the most famous of which is the Jack Hills zircons. These are up to 4.3 billion years old, 300 million years older than the Acasta Gneiss. They are tiny grains of mineral zircon that have been eroded out of their parental rock (the rock in which they initially crystallized).

These zircons are found in much younger sediments in Australia, which means that it’s difficult to determine what kind of rocks these minerals originally came from, leaving open the question of whether there was continental crust during the earliest period of Earth’s history.

Continental connections

In our recent study, we compared all aspects of the chemistry of the zircon crystals from Acasta rocks to the Jack Hills zircons to see if they could have been formed in a similar environment.

Canadian and Australian rocks offer clues about the origin of life

A contrast-enhanced true colour satellite image
(Landsat 5) of the Jack Hills in Western Australia. 
(Image: Gretarsson/CC BY)

We found that the two sets of zircon grains are chemically identical, suggesting that they formed from the same kinds of rocks and likely in the same kinds of tectonic settings. This means that the earth may have started to create continental-type crust very soon after it formed.

The chemical composition of both suites of zircon crystals also suggests that they grew in magmas that originated at great depth in the earth. Deep origins for magmas are a typical sign of subduction on the modern earth.

We compared the amount of uranium in the crystals to the amount of ytterbium, a rare element. When a magma forms at great depth, the mineral garnet is often present, which gathers ytterbium. This means less ytterbium is taken up by zircon crystals, suggesting that a relative lack of ytterbium indicates that these magmas formed in deep environments.

The Jack Hills zircons are known to have crystallized at relatively low temperatures. We found that the temperatures from Acasta zircons matched exactly with the Jack Hills zircons, further indicating their similarity.

Finding the beginning

Ultimately, our results indicate that the tectonic processes occurring at the beginning of the geological record may not have been so different from the processes occurring afterwards. Evidence that things were not much different from modern Earth brings intriguing insights into the potential for the origin of life and the habitability of early Earth, possibly confirming that life was present very early in Earth’s history.

Joshua Davies receives funding from the Natural Sciences and Engineering Research Council of Canada, and l’Université du Québec à Montréal.

Jesse Reimink receives funding from Pennsylvania State University and the U.S. National Science Foundation.
The Conversation

This article is republished from The Conversation under a Creative Commons licence. Read the original article.

Related:





Let’s block ads! (Why?)



Source link

Continue Reading

Science

There's Pink Snow in Europe. That Could Be Bad, Scientists Say – Futurism

Published

on


Dirty Snow

If you were to trek up the Italian Alps right now, you’d find your boots covered in bizarrely pink snow.

While it’s a beautiful touch that turns the mountaintops into an alien landscape, Earther reports that the pink snow is actually a pretty bad sign. The pink color comes from blooming algae. And while the full extent of its impact on the environment is poorly understood, it could speed up the rate at which snow melts away.

What We Know

It’s not so much that the algae is melting the snow itself, Earther reports. But rather, turning the snow into pink “strawberry snow,” as it’s sometimes called, makes it absorb more heat from sunlight, which causes it to melt sooner.

Blooms like this aren’t unheard of — they’re a relatively common occurrence in glaciers in the spring and summer. It’s not yet clear if rising temperatures linked to climate change will mean more blooms in the future, Earther reports, but there is the distinct possibility that more heat will mean more algae and less snow.

Missing Information

Scientists do know that the snow is vanishing from the Alps. And many glaciers could vanish this century, as mild snowfalls fail to replace the melting ice beneath it.

“Less solid precipitation during winter and higher air temperatures during spring and summer are expected to favor the formation of snow- and glacier-algae,” Biagio Di Mauro of Italy’s National Research Council told Earther.

Update: Astute readers pointed out that the snow turns pink on the ground, rather than falling from the sky. Our headline, which originally suggested otherwise, has been updated.

READ MORE: Pink Snow in the Italian Alps Is a Cute Sign of Environmental Catastrophe [Earther]

More on snow: Residents Are Trying To Flee Russian Town Where Snow Turned Black

Let’s block ads! (Why?)



Source link

Continue Reading

Science

Grizzly bears in the dark as they try to share living space with humans: study – BayToday

Published

on


EDMONTON — Grizzly bears are doing their best to get along with people, but it still isn’t enough.

Newly published research concludes that without large wilderness areas to replenish their numbers, grizzlies would disappear from landscapes they share with humans.

“The persistence of bears near people, when we see them along highways or near towns, they’re really propped up by the fact they exist near some sort of secure wilderness,” said Clayton Lamb, a University of Alberta biologist and lead author of a paper published in the Proceedings of the National Academy of Sciences.

Researchers found bears in populated areas in Alberta and British Columbia have even changed how they hunt in an attempt to share living space with humans.

“The bears are doing what they can,” Lamb said. “The difference might have to be made up by us.”

The study set out to examine an emerging phenomenon in wildlife conservation — large carnivores re-establishing themselves on mixed landscapes including cities, highways, rural communities and patchworks of natural habitat.

It digested 41 years worth of mortality, movement and demography among 2,669 grizzlies over nearly 400,000 square kilometres of British Columbia.

It found mortality has increased steeply with the amount of human impact measured through an index that includes human population, land use, infrastructure, coastlines, roads, railroads and navigable rivers.

Deaths have outnumbered births and the difference is being made up through emigration of young grizzlies from nearby wilderness. For every point the index increases, a local bear population must increase the number of individuals it draws by about two per cent.

“Grizzly bear range is quite tied to the distance from some secure piece of wilderness,” said Lamb.

That’s despite the grizzlies’ efforts to adapt to humans. The study found young, newly arrived bears gradually learned ways to avoid contact, such as hunting and gathering at night.

Adolescent bears in areas dominated by humans have increased their nocturnal time by up to three per cent annually, which has led to corresponding increases in survival. The cost, however, is steep. 

The scientists found it takes 14 years for a grizzly to learn how to co-exist with humans. For every bear that makes it, 29 don’t. 

“A lot of those bears would have been born on a mountaintop 10 kilometres away and lived with mom in an avalanche chute and lived a normal bear life,” Lamb said.

“Then they find a home near town and get lured in by an apple tree. The gauntlet they have to run is very difficult.”

The study shows that high mortality has impacts far from where the deaths take place. Bears dying in mixed-used areas draws more grizzlies from the wilderness to take their place. 

“Conflicts with people have rippling effects on (bear) populations far removed,” Lamb said. 

Highway overpasses are one good way to reduce deaths, he suggests. But humans living with bears have to get better at removing attractants such as roadkill or fruit trees to end the bears’ constant, often fatal, migration from the wilderness.  

“We’re not quite there,” said Lamb. “The system relies quite heavily on adjacent wilderness.”

This report by The Canadian Press was first published July 7, 2020

— Follow @row1960 on Twitter

Bob Weber, The Canadian Press

Let’s block ads! (Why?)



Source link

Continue Reading

Science

Bear population attempting to live alongside people, but it’s not enough: study – Globalnews.ca

Published

on


Grizzly bears are doing their best to get along with people, but it still isn’t enough.

Newly published research concludes that without large wilderness areas to replenish their numbers, grizzlies would disappear from landscapes they share with humans.

“The persistence of bears near people, when we see them along highways or near towns, they’re really propped up by the fact they exist near some sort of secure wilderness,” said Clayton Lamb, a University of Alberta biologist and lead author of a paper published in the Proceedings of the National Academy of Sciences.

Read more:
Northern Alberta bear encounter captured on video

Researchers found bears in populated areas in Alberta and British Columbia have even changed how they hunt in an attempt to share living space with humans.

Story continues below advertisement

“The bears are doing what they can,” Lamb said. “The difference might have to be made up by us.”

The study set out to examine an emerging phenomenon in wildlife conservation — large carnivores re-establishing themselves on mixed landscapes including cities, highways, rural communities and patchworks of natural habitat.

It digested 41 years worth of mortality, movement and demography among 2,669 grizzlies over nearly 400,000 square kilometres of British Columbia.

It found mortality has increased steeply with the amount of human impact measured through an index that includes human population, land use, infrastructure, coastlines, roads, railroads and navigable rivers.






0:48
Grouse Mountain bears out of winter hibernation


Grouse Mountain bears out of winter hibernation

Deaths have outnumbered births and the difference is being made up through emigration of young grizzlies from nearby wilderness. For every point the index increases, a local bear population must increase the number of individuals it draws by about two per cent.

Story continues below advertisement

“Grizzly bear range is quite tied to the distance from some secure piece of wilderness,” said Lamb.

That’s despite the grizzlies’ efforts to adapt to humans. The study found young, newly arrived bears gradually learned ways to avoid contact, such as hunting and gathering at night.

Adolescent bears in areas dominated by humans have increased their nocturnal time by up to three per cent annually, which has led to corresponding increases in survival. The cost, however, is steep.






1:45
3 grizzlies spotted in Alberta woman’s backyard


3 grizzlies spotted in Alberta woman’s backyard

The scientists found it takes 14 years for a grizzly to learn how to co-exist with humans. For every bear that makes it, 29 don’t.

“A lot of those bears would have been born on a mountaintop 10 kilometres away and lived with mom in an avalanche chute and lived a normal bear life,” Lamb said.

Story continues below advertisement

“Then they find a home near town and get lured in by an apple tree. The gauntlet they have to run is very difficult.”

The study shows that high mortality has impacts far from where the deaths take place. Bears dying in mixed-used areas draws more grizzlies from the wilderness to take their place.

“Conflicts with people have rippling effects on (bear) populations far removed,” Lamb said.

Read more:
‘Never seen anything like it’: Bear cub spotted in Alberta with unique white head

Highway overpasses are one good way to reduce deaths, he suggests. But humans living with bears have to get better at removing attractants such as roadkill or fruit trees to end the bears’ constant, often fatal, migration from the wilderness.

“We’re not quite there,” said Lamb. “The system relies quite heavily on adjacent wilderness.”

Story continues below advertisement

© 2020 The Canadian Press

Let’s block ads! (Why?)



Source link

Continue Reading

Trending