American Scientist

In this roundup, managing editor Stacey Lutkoski summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief.

Continental Creation

Massive impacts that bombarded the nascent Earth’s surface contributed to the formation of the continents. A team of geoscientists has found the first direct evidence of these collisions in Pilbara Craton in Western Australia. Cratons comprise some of the oldest pieces of Earth and form the cores of the modern continents; the Pilbara Craton was created between 2.5 and 4 billion years ago during the Archaean Eon, when approximately 75 percent of the planet’s continental crust formed. Earth is the only known planet with continents, and there are two main theories as to how they formed: rumblings in the molten mantle from below, or a barrage of impacts from above. Tim E. Johnson of Curtin University in Australia led a team that examined zircons, tiny crystals embedded in the rocks that form the Pilbara Craton. They measured the zircons’ oxygen isotopic compositions for clues as to whether the crystals formed in the mantle or at the planet’s surface. Their findings indicate a top-down process in which giant meteorites crashed into Earth, causing rocks to melt and mix with seawater and meteorite debris to forge the crystals. This molten mixture coalesced into less-dense rocks that rose above the oceans, creating areas of dry land on the previously waterlogged planet. Learning about how the continents formed may offer clues as to how life emerged on Earth and raises the possibility of life on other rocky, ocean planets.

Johnson, T. E., C. L. Kirkland, Y. Lu, R. H. Smithies, M. Brown, and M. I. H. Hartnady. Giant impacts and the origin and evolution of continents. Nature 608:330–335 (August 10).

Tactile Technology

A smart finger that can identify materials and textures by touch creates new possibilities for prosthetic devices. The sense of touch is complicated, incorporating temperature, humidity, pressure, and texture. Previous haptic sensors could identify temperature, humidity, and pressure, but texture and degree of roughness are more difficult to quantify, and thus to program. A team at the Chinese Academy of Sciences Center for Excellence in Nanoscience has developed a way to identify those more nebulous characteristics through machine learning and triboelectric sensing. Triboelectricity is created when compatible materials touch and exchange electrons—the most common example is static electricity. Every material has a unique triboelectric “fingerprint” based on the electrons it gains or loses in these exchanges. When the smart finger comes in contact with an object, its triboelectric sensor measures the interaction and identifies the material. The researchers claim that the technology has a 96.8 percent accuracy rate, making it more precise than a human finger. The smart finger could help people with prosthetic devices artificially feel their surroundings and navigate more easily. It could also have industrial uses, such as sorting materials.

Qu, X., et al. Artificial tactile perception smart finger for material identification based on triboelectric sensing. Science Advances 8(31):eabq2521 (August 5).

Researchers’ Sex Affects Mice

Laboratory mice respond differently depending on whether the human experimenter is male or female. A team led by Todd D. Gould of the University of Maryland School of Medicine exposed mice to the smells of human males and females via cotton swabs that had been rubbed on volunteers and T-shirts worn by experimenters. In both cases, the mice showed an aversion to scents of males but not of females. The mice were then placed in a Y-shaped maze with human male, female, and control scents at each arm. Again, the animals avoided the human male arm, but they were not drawn to the female arm, which suggests that the female scent is preferred but is not rewarding. The differences in the mouse reactions were pharmacological as well as behavioral. Mice injected with ketamine by male researchers were more responsive to the drug than those injected by female researchers. The team found that the stress response in mice handled by males activates specific neurons that aid ketamine’s efficacy. Turning on those neurons in humans might help those who do not respond well to antidepressant therapies. The study also raises questions about the clinical findings and reproducibility of previous mouse studies.

Georgiou, P., et al. Experimenters’ sex modulates mouse behaviors and neural responses to ketamine via corticotropin releasing factor. Nature Neuroscience 25:1191–1200 (August 30).

Never-Ending Life Cycle

Duplicates of antiaging genes make certain types of jellyfish biologically immortal. The standard jellyfish life cycle begins with larvae that develop into polyps and then grow into the adult “medusa” form commonly associated with the animals. Most jellyfish then reproduce, age, and die, but Turritopsis dohrnii, also known as immortal jellyfish, skip that last step. Instead, the creatures shrink into cysts and then return to the polyp stage, where they again grow into a medusa. T. dohrnii are the only known animal species that can repeatedly rejuvenate after sexual reproduction, becoming essentially immortal. Biologists at the University of Oviedo in Spain compared the genome of T. dohrnii with that of the closely related Turritopsis rubra, which has a normal life cycle including death, and identified nearly 1,000 genes related to replication and DNA repair. The immortal jellyfish had duplicates of many of these genes, which might protect their cells from aging. The team’s findings could contribute to the development of antiaging and regenerative medicines for humans.

Pascual-Torner, M., et al. Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation. Proceedings of the National Academy of Sciences of the U.S.A. 119:e2118763119 (August 29).