New study challenges where life first began on Earth

A major impact can eradicate entire ecosystems. It can melt rocks, send debris around the planet, and create a dent in the crust. Additionally, the heat released from the object may provide an environment suitable for the beginning of the process of life.

This concept is explored in a paper recently published in the Journal of Marine Science and Engineering, authored by Shea Cinquemani, a graduate of Rutgers University. Her collaborator Dr. Richard Lutz, an oceanographer at Rutgers, also contributed to the paper.

In their study, they examined the similarities and differences between impact craters and the associated hydrothermal systems that would have resulted from the impact. They compared these systems to deep-sea hydrothermal vents. These vents have been a focus of many scientists when trying to understand the origins of life on Earth.

"We do not know, from a scientific point of view, how life could have been created out of a lifeless early Earth," said Cinquemani. "From where did something come from nothing?"

Heat, water, and chemistry are all present in a deep-sea hydrothermal vent. Hydrothermal vents exist on the ocean floor as a result of tectonic activity. Hydrothermal vents are the only places on Earth that support extremely large numbers of organisms without the assistance of sunlight. Instead of obtaining energy through photosynthesis, organisms living in hydrothermal vents obtain energy from the chemicals contained within the vent fluids using a process known as chemosynthesis.

Conditions in these environments are considered harsh. Many of the fluid temperatures found in hydrothermal vents are near 400 degrees Celsius due to the immense pressures experienced within the vent. The rocks and minerals that surround hydrothermal vents create greater temperature, chemical, and acidity differences than are found in most places on Earth.

According to many researchers, the presence of vents on Earth is likely the key to understanding how prebiotic molecules and early cellular structures originated.

Although the review by Cinquemani does not dispute the aforementioned possibility, it shifts the reader's attention to an alternative setting for hydrothermal processes. These are hydrothermal systems that were not created by molten rock coming up from below the ocean floor. Instead, these systems were formed as a result of the retrograde heat from a meteor impact.

When a large meteor strikes and impacts the Earth, it generates immense heat that melts the surrounding rock. Once the resulting crater fills with water as it cools, hydrothermal circulation may develop within that water. The minerals that form from the hydrothermal circulation will generally have existed for thousands of years, tens of thousands of years, or much longer. The size of the crater and the quantity of heat present in the crater will determine how long the mineral deposits continue to be created.

“In the centre of the crater you have a 'lake' of water that is being heated by the impact,” Cinquemani states. “The water becomes hot. The temperature of the minerals in the hydrothermal system increases as mineralisation occurs due to the temperature differential.”

The review makes a case for how hydrothermal systems can last for tens of thousands of years via multiple hydrothermal systems formed from impacts. Clearly, Cinquemani can point to multiple well-established impact sites throughout different geological periods of the Earth.

For example, the Haughton impact site in Canada is thought to have formed approximately 31 million years ago. It has hydrothermal evidence showing it formed in a slow, controlled way over a long period of time. Thus, it is theorized that the mineralisation of Haughton creates long-term hot conditions. Therefore, during this time period, the environment at Haughton was conducive to supporting life for a long time.

India's Lonar Lake, estimated at only 50,000 years old, provides scientists with the opportunity to study microbial signatures left in the debris created by the impact that formed it on Earth. One caveat noted by Cinquemani is that, by this time in Earth's history, life had already spread over a large portion of the planet. Therefore, any DNA found in Lonar Lake will likely represent contamination and not life which originated there.

Chicxulub, on the Yucatan Peninsula of Mexico, is an impact structure formed as a result of the same catastrophic event that caused the extinction of dinosaurs 65 million years ago. The review describes Chicxulub as a massive hydrothermal system. This system contained iron- and sulfur-rich fluids for approximately two million years. Therefore, life-molecule complexity was possible, and microbial colonization may have occurred.

Cinquemani's review raises the question of whether life molecules could have developed in a stable environment long enough for simple molecules to form more complex molecules. The review argues that impact-generated systems must have provided energy and sufficient time to enable this.

Additionally, the author of this paper suggests that these crater systems may meet the criteria for the origin of life better than deep-sea vents.

One example of this is the water paradox, which indicates that a thriving organism requires water for its survival. Yet, excessive water will decompose biomolecular structures. Many research experts have documented how the drying and wetting of certain bio-organisms would have enabled them to solve the water paradox. Although deep-sea environments may be less conducive to supporting life than other environments, this review found that shallow crater lakes may have allowed for the development of life through cycles that were more favorable.

The review identified several benefits of the impact-generated systems that Cinquemani discussed in her publication. These benefits include freshwater, exposure of mineral ore to chemical gradients, and possibly the presence of serpentinization, which is a rock-water reaction that produces hydrogen.

However, the research does not establish an absolute timeline for the emergence of life. For example, the evidence currently available older than 3.5 billion years remains controversial. Theories of the origin of life range from RNA-first to metabolism-first. The paper is a literature review rather than an experimental study. Thus the reliability of evidence from younger locations, such as Lonar, is questionable.

Her decision to research the topic stems from that uncertainty.

"I thought, 'This is the first time I will be working with a subject area where I know absolutely nothing,'" she said of the class project that became Cinquemani's paper. "Just thinking about the possible origins of biology on a different planet was overwhelming. I didn't know how I would get started."

Lutz commented that this review paper underwent a particularly arduous process for publication.

"I have never seen such a stringent review process," he remarked. "There were 15 pages of reviewer comments and 5 separate rounds of peer review. She displayed incredible dedication and diligence, and the resulting article is phenomenal."

The review creates a larger area on the map for scientists searching for the origins of life because it provides a complementary focus of research on ancient impact craters and associated hydrothermal systems.

This is in addition to the traditional focus on deep oceans. This change will be relevant to future research on Earth because of the scarcity of evidence toward the very beginnings of life.

It will also be relevant when searching for signs of life within potential hydrothermal systems on icy moons such as Europa and Enceladus, or within the impact crater systems of early Mars.

Research findings are available online in the Journal of Marine Science and Engineering.

The original story "New study challenges where life first began on Earth" is published in The Brighter Side of News.

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