Category: Early Earth (page 1 of 4)

New Findings Suggest the Building Blocks For Life’s Genetic Structure May Well Have Arrived From Above

Conceptual image of meteoroids delivering nucleobases to ancient Earth. The nucleobases are represented by structural diagrams with hydrogen atoms as white spheres, carbon as black, nitrogen as blue and oxygen as red. (NASA Goddard/CI Lab/Dan Gallagher)

All of life, from simplest to most complex, contains five information-passing compounds that allow the genetic code to work.  These nitrogen-based compounds, called nucleobases, are found in all the the DNA and RNA that  provide the instructions to build and operate every living thing on Earth.

How these compounds are formed, or where they come from, has long been a key question in astrobiology and the search for the origin of life.

Numerous theories have been advanced to explain their presence, including that they arrived on Earth via meteorites and the infall of dust.  But until recently, only three of these nucleobases have been found embedded in meteorites but, puzzlingly, the two others have not been found.

Now an international team centered in Japan has completed the search for nucleobases in meteorites by finding the remaining two, and so it appears possible that all these building blocks of the genetic code could have arrived on very early Earth from afar.

Yasuhiro Oba of the University of Hokkaido, and lead author of the new study in Nature Communications, said that  extraterrestrial material arrived in much greater quantities on the early Earth — during what is called the period of “late heavy bombardment” — and so the discovery “of all five primary nucleobases in DNA/RNA indicates that these components should have been provided to the early Earth with such extraterrestrial materials.”

This certainly does not mean that fully formed DNA or RNA was delivered to Earth.  Oba said the process of making those nucleic acids from components parts, including nucleobases, is under active study but is not particularly well understood.  But it does mean that essential building blocks for the genetic backbone of life clearly did arrive from space for possible use in the life-forming process.

“We don’t know how life first started on the Earth, but the discovery of extraterrestrial nucleobases in meteorites provides additional support for the theory that meteorite delivery could have seeded the early Earth with the fundamental units of the genetic code found in DNA and RNA in all life today,” said co-author Daniel Glavin of NASA’s Goddard Spaceflight Center.

“These nucleobases are highly soluble in liquid water, so over time, any meteorite fragments exposed to water on the early Earth would be extracted from the meteorites into the water and could therefore contribute to the chemical inventory of the prebiotic soup from which life emerged.”… Read more

Can We Trust a Handful of Grains to Tell Us About the Early Earth? A Look at the Hayabusa2 Asteroid Sample

The Hayabusa2 sample return capsule returning to Earth. The bright streak in the sky is the capsule, shock heated as it enters the Earth’s atmosphere. The bright lights on the ground are buildings. (JAXA)

In the early hours of December 6, 2020, what appeared to be a shooting star blazed across the sky above the Woomera desert in South Australia. The source was the sample return capsule from JAXA’s Hayabusa2 mission, which contained precious material from a near-Earth asteroid known as Ryugu.

Within 60 hours, the capsule had been retrieved and flown to the curation facility at JAXA’s Institute of Space and Astronautical Science in Japan. In vacuum conditions to prevent any trace of contamination, the capsule was opened to reveal over 5 grams of asteroid grains.

This material is expected to have undergone little change since the early days of the solar system some 4.5 billion years ago, and its highly anticipated analysis could provide new information about how the Earth acquired water and organics needed to begin life. The sample is the first ever collected from a carbonaceous (C-type) asteroid, which resemble primitive meteorites found to have a chemical composition close to that of the Sun.

Tet despite a rigorously planned and executed journey of over 5,000 million kilometers to bring back a pristine sample from space, concerns have remained. Chief among these are whether the rocky grains in the sample capsule were typical of the asteroid.

If the Hayabusa2 spacecraft had inadvertently gathered grains from an unusual spot, or if the grains had been altered during the collection and return to Earth, then deductions about the asteroid’s composition–and therefore our solar system’s past–could be wrong.  

The sample from asteroid Ryugu (from Yada et al. Nature Astronomy 2021)

The Hayabusa2 team had already gone to rather extreme lengths to mitigate this issue.

In addition to the rapid retrieval operation that ensured that the sample was not contaminated by our planet’s atmosphere, the spacecraft had performed the dangerous landing twice on the surface of asteroid Ryugu to collect samples from two separate sites.

One of these locations was close to where the spacecraft had made an artificial crater, ejecting material from beneath the asteroid’s surface to be gathered during the second collection operation. Rocky grains from below the top layer surface are expected to be particularly pristine, as they have been protected from the bombardment of sunlight, cosmic rays and micrometeorites.… Read more

The Surface of Venus Was Thought to Be Stagnant. But This May Not Be True

An oblique radar view of the largest “pack ice” block in the Venus lowlands identified by Byrne et al. (Paul Byrne, based on original NASA/JPL imagery).

The two Earth-sized planets in our solar system have taken wildly different evolutionary routes. The surface of the Earth became a temperate utopia for a liquid water and a myriad of life. But while similar in both size and mass, the surface of the neighboring Venus is hot enough to melt lead.

These differences are the key to understanding the possible outcomes for a rocky planet after it forms out of the dusty disk around a young star. Knowledge of the rocky options is needed to identify the surface environments of extrasolar planets from the limited data we can gleam through our telescopes, and to unpick the properties needed to form a habitable planet. It is a task considered so important that three new Venus missions were approved by NASA and ESA in the last month.

(Read about these missions on Many Worlds here and here)

One such difference between the Earth and Venus is the type of planet surface or, more precisely, the structure of the planet lithosphere that comprises of the crust and uppermost part of the mantle.

The Earth’s lithosphere is broken into mobile chunks that can subduct beneath one another, bunch up to form mountain rages, or pull part. This motion is known as plate tectonics, and it allows material to be cycled between our surface and the hidden mantle deep below our feet. It is a geological process that replenishes nutrients, cools the planet interior, and also forms part of the Earth’s carbon cycle that adjusts the levels of carbon dioxide in our atmosphere to keep our environment temperate. Without this cycling ability, the Earth would not have been able to stay habitable over such a long period.

Venus and the Earth are extremely close in size and mass. Yet, only the Earth developed plate tectonics (ESA).

By contrast, the lithosphere of Venus does not form plates. This prevents carbon from being drawn into the mantle, and any nutrients below the surface are unreachable. Indeed, the surface of Venus has long been thought to be a single piece of immobile, stagnant lid, with no connection at all with the planet interior.

Not only does the lack of geological processes throttle Venus’s environment, the seemingly complete immobility of the lithosphere was extremely annoying.… Read more

New Insights Into How Earth Got Its Nitrogen

An artist’s conception shows a protoplanetary disk of dust and gas around a young star. New research by Rice University shows that Earth’s nitrogen came from both inner and outer regions of the disk that formed our solar system, contrary to earlier theory.  (NASA/JPL-Caltech)

Scientists have long held that many of the important compounds and elements that make life possible on Earth arrived here after the planet was formed and was orbiting the sun.  These molecules came via meteorites and comets, it was thought,  from the colder regions beyond Jupiter.

But in a challenge to that long-accepted view, a team from Rice University has found isotopic signatures of nitrogen from both the inner and the outer disk in iron meteorites that fell to Earth.  What this strongly suggests is that the seeds of rocky, inner solar system planets such as Earth were bathed in  dust that contained nitrogen and other volatiles, and the growing planet kept some of that “local” material.

“Our work completely changes the current narrative,” said Rice University graduate student and lead author Damanveer Grewal. “We show that the volatile elements were present in the inner disk dust, probably in the form of refractory (non-gaseous) organics, from the very beginning. This means that contrary to current understanding, the seeds of the present-day rocky planets — including Earth — were not volatile-free.”

The solar protoplanetary disk was separated into two reservoirs, with the inner solar system material having a lower concentration of nitrogen-15 and the outer solar system material being nitrogen-15 rich. The nitrogen isotope composition of present-day Earth lies in between, according to a new Rice University study that shows it came from both reservoirs. (Credit: Illustration by Amrita P. Vyas)

This work helped settle a prolonged debate over the origin of life-essential volatile elements — such as hydrogen, water, carbon dioxide, methane, nitrogen, ammonia — on Earth and other rocky bodies in the solar system.

“Researchers have always thought that the inner part of the solar system, within Jupiter’s orbit, was too hot for nitrogen and other volatile elements to condense as solids, meaning that volatile elements in the inner disk were only in the gas phase,” Grewal said.

Because the seeds of present-day rocky planets, also known as protoplanets, grew in the inner disk by accreting locally sourced dust, he said it appeared they did not contain nitrogen or other volatiles because of the high temperatures, necessitating their delivery from the outer solar system.… Read more

The Faint Young Sun Paradox and Mars

This NASA image of Mars at sunset taken by the Spirit  rover, evokes the conditions on early Mars when the planet received only 70 percent of the of the solar energy that it does now.  (NASA/JPL/Texas A&M/Cornell)

When our sun was young, it was significantly less luminous and sent out significantly less warming energy than it does now.  Scientists estimate that 4 million years ago, when the sun and our solar system were 500 million years old, the energy that the sun produced and dispersed was about 75 percent of what it is today.

The paradox arises because during this time of the faint young sun Earth had liquid water on its surface and — as has been conclusively proven in recent years — so did Mars, which is 61 million miles further into space.  However difficult it is to explain the faint young sun problem as it relates to early Earth, it is far more difficult to explain for far more frigid Mars.

Yet many have tried.  And because the data is both limited and innately puzzling, the subject has been vigorously debated from a variety of different perspectives.  In 2018, the journal Nature Geoscience published an editorial on the state of that dispute titled “Mars at War.”

There are numerous point of (strenuous) disagreement, with the main ones involving whether early Mars was significantly more wet and warm than previously inferred, or whether it was essentially cold and arid with only brief interludes of warming.  The differences in interpretation also require different models for how the warming occurred.

Was there a greenhouse warming  effect produced by heat-retaining molecules in the atmosphere?  Was long-term volcanic activity the cause? Or perhaps meteor strikes?  Or heat from the interior of the planet?

All of these explanations are plausible and all may have played a role.  But that begs the question that has so energized Mars scientists since Mars orbiters and the Curiosity rover conclusively proved that surface water created early rivers and valley networks, lakes and perhaps an ocean.  To solve the “faint young sun” paradox as it played out on Mars,  a climate driver (or drivers) that produces significant amounts of heat is required.

Could the necessary warming be the result of radioactive elements in the Martian crust and mantle that decay and give off impressive amounts of heat when they do?

A team led by Lujendra Ojha, an assistant professor at Rutgers University, proposes in Science Advances that may well be the answer, or at least part of the answer.… Read more

An “Elegant” New Theory on How Earth Became a Wet Planet

About 71 percent of the Earth’s surface is covered by water, and vast quantities of water are also locked up in minerals on and beneath the surface.  This image of Earth comes from NASA’s Earth Polychromatic Imaging Camera (EPIC) on NOAA’s Deep Space Climate Observatory (DSCOVR), orbits Earth from a distance of about 1 million miles away. (NASA)

One of the enduring puzzles of our planet is why it is so wet.

Since Earth formed relatively close to the sun,  planetary scientists have generally held that any of the water in the building blocks of early-forming Earth was baked out and so was unavailable to make oceans or our atmosphere.

That led to theories explaining the oceans and wet atmosphere of Earth as a later addition, brought to us by meteorites and comets formed beyond the solar system’s so-called “snow line,” where volatile compounds such as water can begin to condense into ice.

This snow line is a general area between Mars and Jupiter, and that means under this theory that our water would have had to come from awfully far away.   Further complicating this view is that the isotopic makeup of that distant water ice is somewhat different from much of the water on Earth.

Now, a new paper in the journal Science from Laurette Piani of  the Université de Lorraine and colleagues, argues that Earth’s water was simply acquired like most other of our materials, through accretion when the planet formed in the inner solar nebula.

To reach that conclusion, the group re-examined 13 meteorites of the parched type formed between Earth and the sun, and they found more than of enough hydrogen present to explain how Earth got so wet (wet for our solar system, that is.)

In fact, they extrapolated from their data that enough water was available in the nebular cloud  that accompanied the formation of our sun and formed those early meteorites — called enstatite chondrites — to create three times as much water as our oceans hold.

 

 

New measurements of enstatite chondrites indicate that water could have been primarily acquired from Earth’s building blocks. Additional water was delivered to Earth’s early oceans and atmosphere by water-rich material from comets and the outer asteroid belt. (Science)

“Our discovery shows that the Earth’s building blocks might have significantly contributed to the Earth’s water and that hydrogen bearing material was present in the inner solar system at the time of the Earth and rocky planet formation, even though the temperatures were too high for water to condense,'” Piani told me.… Read more

Cores, Planets and The Mission to Psyche

The asteroid Psyche will be the first metal-rich celestial body to be visited by a spacecraft.  The NASA mission launches in 2022 and is expected to arrive at the asteroid in late 2026.  A central question to be answered is whether Psyche is the exposed  core of a protoplanet that was stripped of its rocky mantle. (NASA)

Deep inside the rocky planets of our solar system, as well as some solar system moons,  is an iron-based core.

Some, such as Earth’s core,  have an inner solid phase and outer molten phase, but the solar system cores studied so far are of significantly varied sizes and contain a pretty wide variety of elements alongside the iron.  Mercury, for instance, is 85 percent core by volume and made up largely of iron, while our moon’s core is thought to be 20 percent of its volume and is mostly iron with some sulfur and nickel.

Iron cores like our own play a central role in creating a magnetic field around the planet, which in turn holds in the atmosphere and may well be essential to make a planet habitable.  They are also key to understanding how planets form after a star is forged and remaining dense gases and dust are kicked out to form a protoplanetary disk, where planets are assembled.

So cores are central to planetary science, and yet they are obviously hard to study.  The Earth’s core starts about 1,800 miles below the surface, and the cores of gas giants such as Jupiter are much further inward, and even their elemental makeups are not fully understood.

All this helps explains why the upcoming NASA mission to the asteroid Psyche is being eagerly anticipated, especially by scientists who focus on planetary formation.

Scheduled to launch in 2022, the spacecraft will travel to the main asteroid belt between Mars and Jupiter and home in on what has been described as an unusual “metal body,”  which is also one of the largest asteroids orbiting the sun.

While some uncertainty remains,  it appears that Psyche is the  exposed nickel-iron core of a long-ago emerging rocky protoplanet, with the rest of the planet stripped away by collisions billions of years ago.

An artist’s impression of solar system formation, and the formation of a protoplanetary disk filled with gases and dust that over time clump together and smash into each other to form larger and larger bodies. (Gemini Observatory/AURA artwork by Lynette Cook )

That makes Psyche a most interesting place to visit.… Read more

Viruses, the Virosphere and Astrovirology

An electron microscopic image of the 2019 novel coronavirus grown in cells at The University of Hong Kong.  Thin-section electron micrographs of the novel coronavirus show part of an infected cell, grown in a culture, with virus particles being released from the cell’s surface. (The University of Hong Kong)

 

When the word “virus” first came into use, it was as a “poison” and “a very small disease-causing agent.”  While the presence of viruses was theorized earlier, they were not fully identified until the 1890s.

So from their earliest discovery, viruses were synonymous with disease and generally of the ghastly epidemic type of disease we now see with coronavirus.  Few words carry such a negative punch.

Without in any way  minimizing the toll of viruses on humans (and apparently all other living things,) men and women who study viruses know that this association with disease is far too restrictive and misses much of what viruses do.  It’s perhaps not something to argue while a viral pandemic is raging, but that’s when the focus on viruses is most intense.

Here, then, is a broader look at what viruses do and have done — how they inflict pandemics but also have introduced genes that have led to crucial evolutionary advances, that have increased the once-essential ability of cyanobacteria in early Earth oceans to photosynthesize and produce oxygen, and that have greatly enhanced the immunity systems of everything they touch.  They — and the virosphere they inhabit — have been an essential agent of change.

Viruses are also thought to be old enough to have played a role — maybe a crucial role — in the origin of life, when RNA-like replicators outside cells may have been common and not just the domain of viruses.  This is why there is a school of thought that the study of viruses is an essential part of astrobiology and the search for the origins of life.  The field is called astrovirology.

Viruses are ubiquitous — infecting every living thing on Earth.

Virologists like to give this eye-popping sense of scale:  based on measurements of viruses in a liter of sea water, they calculate the number of viruses in the oceans of Earth to be 10 31.  That is 10 with 31 zeros after it.  If those viruses could be lined up, the scientists have calculated, they would stretch across the Milky Way 100 times.

“The vast majority of viruses don’t care about humans and have nothing to do with them,” said Rika Anderson,  who studies viruses around hydrothermal vents and teaches at Carleton College in Minnesota. … Read more

Tales From the Deep Earth

Cross section of the varying layers of the Earth .  (Yuri Arcurs via Getty images)

When especially interesting new planets are discovered in the cosmos, scientists around the world begin the process of identifying their characteristics — their orbit, their mass and density,  their composition, their thermal properties and much more.  It’s all part of a drive that seems to be innate in humans to learn about the workings of the world (or worlds) around us.

This began millennia ago when our distant ancestors started to learn about the make-up and processes of Earth.   We now know enormous amounts about our planet, but I was recently introduced to a domain where our knowledge has some substantial holes.  The area of the Earth least well understood is, not surprisingly, what lies deep below us, in the mantle — the inner 2,900 kilometers (2000 miles) of the planet between the outer crust and the iron core.

The on-going exploration of this vast region — made up substances including some which cannot remain intact on the Earth’s surface — struck me as in some ways comparable to the study of exoplanets.   It’s also a realm where scientific observation is limited, but what knowledge is gained then leads through induction, deduction, modeling and exacting lab work to a gradual expansion back of our knowledge.

And in the case of some high-temperature, high-pressure minerals, this has led to a most unusual technique for identifying and naming key components of our inner planet.  Unable to reach or preserve some of the most important components of the mantle,  geochemists and other deep Earth scientists go to incoming meteorites to learn about what’s beneath (deeply beneath, that is) our feet.

With this in mind, here is a look at the discovery and recent naming of the mineral hiroseite, an unusual but quite widespread component of the very deep Earth.

 

ELSI director Kei Hirose has been honored for his pioneering work in identifying and describing components of the Earth’s lower mantle. In recognition of his work, a newly identified lower mantle mineral has been given the name of hiroseite. (Nerissa Escanlar)

 

It was two decades ago when Kei Hirose – a Japanese geochemist expert in high-pressure, deep-Earth phenomena, then at the Tokyo Institute of Technology – began researching a long-standing problem in understanding the working of the lower depths of our planet’s enormous mantle: the last 300 kilomiles above the boundary with the scalding iron core.

Read more

Using Climate Science on Earth to Understand Planets Beyond Earth

Climate expert Tony Del Genio has just retired after 41 years-plus at NASA’s Goddard Institute of Space Studies (GISS) in New York City. Here Del Genio is attending a Cubs game at Wrigley Field with (from the lower right) Dawn Gelino, Shawn Domogal-Goldman, Aaron Gronstal and Mary Voytek. All are part of the NASA NExSS initiative. (Dawn Gelino)

Anthony Del Genio started out his career expecting to become first an engineer and then a geophysicist.  He was in graduate school at UCLA and had been prepared by previous mentors to enter the geophysics field.  But a 1973 department-wide test focused on seismology, rather than fields that he understood better, and his days as a geophysicist were suddenly over.  Fortunately,  one of his professors saw that he had done very well in the planetary atmospheres and geophysical fluid dynamics sections of the exams, and suggested a change in focus.

That turned out to be a good thing for Del Genio, for the field of climate modeling, and for NASA. Because for the next four decades-plus, Del Genio has been an important figure in the field of climate science — first modeling cloud behavior and climate dynamics on Earth with ever more sophisticated atmospheric general circulation models (GCMs), and then beginning to do the same on planets beyond Earth.

His entry into the world of Venus, Saturn, Titan and distant exoplanets beyond is how I met Tony in 2015. At the same time that Many Worlds began as a column, Del Genio was named one of the founding leaders of the Nexus for Exoplanet System Science (NExSS) — the pioneering, interdisciplinary NASA initiative to bring together scientists working in the field of planetary habitability.  (NExSS also supports this column.)

Del Genio is a hard-driving scientist, but also has a self-deprecating and big-picture, poetic side.  This came across at our first diner breakfast together on Manhattan’s Upper West Side (where GISS is located), and was highlighted in a piece that Del Genio just wrote for a new series initiated by the American Geophysical Union (AGU),  Perspectives of Earth and Space Scientists.   In that series, scientists are asked to look back on their careers and write about their science and journeys.  Del Genio’s perspective is the first in this series, and I will reprint most of its bottom half because I found it so informative and interesting.

But first, a quote from Del Genio’s piece that sets the stage:  “The beauty of science, if we are patient, is that nature reveals its secrets little by little, slowly enough to keep us pressing forward for more but fast enough for us not to despair.”… Read more

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