The research results may explain how life arose on Earth and can also be applied to other planets and bodies in the solar system and to exoplanets.
Carbonaceous materials from the Ryugu asteroid
A detailed study of samples from the Ryugu asteroid has provided further evidence that the organic molecules that gave rise to life on our planet were brought here by ancient comets. These space rock samples were returned to Earth by Japan’s Hayabusa2 mission, which visited the spinning top-shaped Ryugu space rock in 2018. Hayabusa2 spent about 18 months studying the asteroid and collecting surface material that turned out to be a treasure trove of information about our solar system.
A team of scientists behind new developments in the search for the origins of life have discovered “melt spatters” ranging from 5 to 20 micrometers wide, formed when comet dust in particular pelted the surface of Ryugu. And inside these melt splashes, researchers found small carbonaceous materials similar to primitive organic matter. Ryugu, officially known as 162173 Ryugu, is a 2,850-foot-wide (870-meter-wide) near-Earth asteroid with no protective atmosphere. This means that its surface is directly exposed to space and can collect interplanetary dust, which changes the composition of the asteroid’s surface upon impact.
Asteroid Ryugu. Top – Melt splashes from the surface of Ryugu, bottom – CT slice of the melt showing voids. JAXA/ Megumi Matsumoto et al.
The melt spatter the team studied occurred when the asteroid’s surface material collided with comet dust, with the two materials melting and mixing with each other during the heating caused by the impact and eventually cooling. The spongy carbonaceous materials found in the Ryugu melts are chemically different from the organic matter typically found in cometary material because they lack oxygen and nitrogen. However, this could indicate how the material formed in the first place.
“This organic matter may be small seeds of life once brought from space to Earth,” Megumi Matsumoto, a team member and associate professor at Tohoku University Graduate School of Life Sciences, said in a statement.
“We speculate that the carbonaceous materials were formed from cometary organic matter as a result of the evaporation of volatiles such as nitrogen and oxygen during the heating caused by the impact,” Matsumoto said. “This suggests that cometary material was transported into the near-Earth region from the outer solar system.”
CT scans show carbonaceous material found in the melt spatter from Ryugu. Megumi Matsumoto et al.
Further evidence of the origin of organic matter is the tiny voids created by impacts that released water vapor from materials on Ryugu’s surface; this water was then captured by the impact-heated substance. “Our 3D CT images and chemical analysis showed that the melt spatter consists mainly of silicate glasses with voids and small inclusions of spherical iron sulfides,” Matsumoto added. “The chemistry of the melt spatter suggests that Ryugu hydrous silicates were mixed with comet dust.”
Matsumoto and his team continue to examine Ryugu samples collected by Hayabusa2 in hopes of finding more melts that may contain evidence of comet dust impacts. It is hoped that this will provide a better understanding of the transport of primordial organic material into space around the Earth more than 4 billion years ago, before the emergence of life.
Comets tend to exist in wide orbits around the Sun, meaning they spend most of their time at the cold outer edges of the Solar System. But as they penetrate into the inner solar system, solar radiation heats their icy interior material. This causes the material to turn directly into a gas, a process called sublimation.
When this gaseous material escapes from the comet, it carries some of the object’s surface material with it. This not only creates the characteristic tails and auras, or “comas,” of comets, but also leaves trails of cometary dust around the Sun. When the Earth follows these trails, we witness meteor events as dust fragments burn up in our planet’s atmosphere. However, this cometary material is much more likely to end up on the surface of bodies without an atmosphere, such as Ryugu, where it can be preserved. Thus, studying these dust remnants on Hayabusa2 samples could provide clues about the material of the early Solar System.
Interstellar ice chelating agents
Astrophysicists believe, early forms of life must have contained biomolecules in the form of RNA and amino acids. Metal ions play a key role in stabilizing and copying RNA. Modern cells use special proteins to transport ions across membranes, but they are too large and complex and could hardly have existed at the time of the first protocells. According to scientists, ions could be transported in ancient cells with the help of chelating agents that arose in interstellar ice in space and fell along with meteorites to Earth.
Astrophysicists from Korolev Samara University, together with American colleagues, have theoretically and experimentally proven the possibility of organic substances appearing in space, which fell to Earth along with meteorites and created conditions for the development of life, the press service of the Samara university reported.
“The scientific significance of our research is that for the first time in the world, organic chelating agents were obtained in analogues of interstellar ice. According to many scientists, chelating agents were essential for the existence and development of the first biological protocells. These substances facilitate the transfer of metal ions through the cell membrane , and thus they could participate in the catalysis of RNA replication, that is, in the copying of RNA data and the division of ancient protocells,” said one of the authors of the study, Associate Professor of the Department of Physics at Samara University Ivan Antonov.
The university clarified that the theoretical part of the study was carried out at Samara University, and the experimental part at the University of Hawaii in the USA. Antonov noted that calculations and experiments showed a plausible mechanism for the formation of complex organic matter inside interstellar ice in deep space. “This fundamentally expands knowledge about the achievable level of molecular complexity of organic molecules in space,” the specialist emphasized.
In everyday life, people almost daily encounter chelating agents – they are used in various detergents, washing powder, shampoos, cosmetics, as well as in the restoration of archaeological finds, as they easily remove rust.
chelated form of fertilizers
Soda lakes may resemble Darwin’s “little warm ponds” where life on Earth began
A team of scientists from the University of Washington made this discovery when they discovered a shallow “soda lake” in western Canada that appears to have the chemistry and conditions necessary for a small body of water to facilitate the spontaneous synthesis of complex molecules that led to the emergence of life on Earth around 4 billion years ago.
Soda lakes, like the one discussed in this study, are small bodies of water that contain high levels of dissolved carbonates and sodium, similar to how large quantities of baking soda are dumped into them. However, in this case, the high levels of dissolved sodium and carbonate are caused by reactions between water and volcanic rocks.
Chance Lake in Canada is a soda lake that may represent Darwin’s “little warm pools” where life on Earth began. Kimberly Poppy Sinclair/University of Washington
Since the 1950s, researchers have been able to make biological molecules such as amino acids and the building blocks of RNA from inorganic molecules, but there has been a long-standing problem with the next step in the process. RNA and DNA, the key molecules of life, as well as the membranes of living cells require phosphates. The required concentration of phosphates to form biomolecules used in laboratories is 1 million times higher than the level typically found in rivers, lakes or oceans. This has become known as the “phosphate problem” in theories of the origin of life on Earth, and new research suggests soda lakes could be a solution to this problem.
In addition to high levels of dissolved carbonates and sodium, soda lakes also contain high levels of phosphates. A 2019 study found that concentrations of these molecules in these small bodies of water could be 1 million times higher than in typical bodies of water. This means that soda lakes could be an ideal place for life’s key molecules to emerge.
To test this, the University of Washington began researching just such a soda lake, stopping at Last Chance Lake, a 1-foot (30 cm) deep muddy lake found at the end of a dirt road on the Cariboo Plateau in British Columbia, Canada. This particular soda lake was found to have the highest known phosphate levels in the 1990s.
At the bottom of Last Chance Lake is volcanic basalt rock, this lake is located in a dry, windy climate that keeps water levels low and dissolved compounds concentrated due to the rapid evaporation of incoming water. The scientists behind this new study visited the lake three times between 2021 and 2022, both in summer and winter.
By studying samples of water, lake sediments and salt crust found in Last Chance Lake, the team found that calcium combined with abundant carbonate and magnesium to form dolomite. This is different from the situation in other lakes, where phosphate usually binds with calcium to form calcium phosphate, which forms, for example, the enamel on our teeth and is insoluble, reducing phosphate levels.
A salt crust recovered from Last Chance Lake, with green algae and black sediment at the base. David Catling/University of Washington
As a result of calcium being locked into the dolomite in Last Chance Lake, there is a lot of free phosphate left behind; if these conditions had been found in water basins about 4 billion years ago, it would have allowed the key ingredients responsible for the emergence of the chemistry of life to exist in the required high concentrations. “You have this seemingly dry salt flat, but it has nooks and crannies. And between the salt and the sediment, there are little pockets of water with really high levels of dissolved phosphate,” said team member and Washington University postdoctoral fellow Sebastian Haas.
“We wanted to understand why and when this could have happened on ancient Earth, how it could have become the cradle of life.” The team showed that soda lakes like Last Chance are the most likely places where life on Earth could have originated. In addition, they expect that the same conditions will be possible for other bodies in the Solar System and on all planets outside the Solar System, including exoplanets.
“We were studying a natural environment that should be common to the entire solar system,” Haas said. “Planetary surfaces are dominated by volcanic rocks, so the same water chemistry could have occurred not only on early Earth, but also on early Mars and early Venus if liquid water had been present. These new findings will help inform origins of life researchers who are either replicating these reactions in the laboratory or searching for potentially habitable environments on other planets,” Catling concluded.
The results could help solve a long-standing problem of explaining how life originated on Earth, and could also be applied to other planets in the solar system, such as Mars and Venus. “I think these soda lakes provide the answer to the phosphate problem,” David Catling, senior author of the study and professor of earth and space sciences at the University of Washington, said in a statement. “Our answer is encouraging: this environment must have arisen on early Earth and perhaps on other planets, because it is just a natural result of how planetary surfaces are created and how water chemistry works.”