This article lists a number of significant events in science that have occurred in the second quarter of 2021.
Events April
2 April – Scientists report that the event that caused the mass-extinction of non-avian dinosaurs gave rise to neotropical rainforest biomes like the Amazonia, replacing species composition and structure of local forests. During ~6 million years of recovery to former levels of plant diversity, they evolved from widely spaced gymnosperm-dominated forests to the forests with thick canopies which block sunlight, prevalent flowering plants and high vertical layering as known today.
6 April A study finds that carbon emissions from Bitcoin mining in China – where a majority of the proof-of-work algorithm that generates current economic value is computed, largely fueled by nonrenewable sources – have accelerated rapidly, would soon exceed total annual emissions of European countries like Italy and Spain in 2016 and interfere with climate change mitigation commitments. COVID-19 pandemic: Scientists report the "estimated incidence of a neurological or psychiatric diagnosis in the following 6 months" after diagnosed COVID-19 infection was 33.62% with 12.84% "receiving their first such diagnosis" and higher risks being associated with COVID-19 severity.
7 April Physicists report that results from muon g-2 studies involving the muon subatomic particle challenge the Standard Model and, accordingly, may require an updating of currently understood physics. NOAA reports the largest annual increase in methane emissions since records began, with a rise of 14.7 parts per billion (ppb) in 2020. A study finds that humans engaged in problem-solving tend to overlook subtractive changes, including those that are critical elements of efficient solutions. This tendency to solve by creating or adding elements is shown to intensify with higher cognitive loads in the case of individuals. Scientists report one of the two oldest known reconstructed modern human genomes to date (~45.000 ya) which was found in Koněprusy Caves, Czech Republic, includes long Neanderthal segments and considered to be close to a population that later branched to present-day Europeans and Asians. Scientists confirm, with new genomic data, that initial European modern humans mixed with Neanderthals with continuity to later people in Eurasia and report that such admixture appears to have been more common than previously thought. 8 April – Scientists report rough spectral signatures of 958 molecules that may be involved in the atmospheric production or consumption of phosphine, which could prevent misassignments and, if accuracy is improved, be used in future detections and identifications of molecules on other planets such as Venus. On 10 April, a news report informs about a launched NASA-funded mission to design and test robotic balloons for future scientific exploration of Venus. On 19 April scientists who reported the detection of well-established or likely biosignature, monophosphine, on Venus publish a preprint recovering the detection of PH3 in the Venusian atmosphere – which was challenged by critical studies – with the proposed SO2-attribution alternative being inconsistent with the available data. 9 April Neuralink reveals a male macaque with chips embedded on each side of its brain, playing a mind-controlled version of Pong. Scientists show that the brains of early Homo from Africa and Dmanisi, Western Asia "retained primitive, great ape-like organization of the frontal lobe" until ~1.5 million years ago and therefore long after Homo emerged and first dispersed from Africa – much later than previously thought (~2.5 Mya). Scientists present a tool for epigenome editing, CRISPRoff, that can heritably silence the gene expression of "most genes" and allows for reversible modifications. 12 April The magazine Scientific American announces that it will stop using the term "climate change" in articles about human-caused global warming and substitute "climate emergency" instead. News outlets report that the first prototype 3D printed house made out of clay, Tecla, has been completed. The low-carbon housing was printed by two large arms from a mix that includes locally sourced soil and water. Such buildings could be highly cheap, well-insulated, stable, get produced rapidly, require only very little easily learnable manual labor, mitigate carbon emissions from concrete, require less energy, reduce homelessness, help enable intentional communities, and enable the provision of housing for victims of natural disasters as well as for migrants to Europe near their homes, rather than political facilitation of their influx. Scientists develop a prototype and design rules for both-sides-contacted silicon solar cells with conversion efficiencies of 26% and above, Earth's highest for this type of solar cell. 13 April Scientists report the discovery of a billion-years-old, likely holozoan, protist, Bicellum brasieri, showing that the evolution of differentiated multicellularity – such as of animal lineages – occurred at least 1 bn years ago and possibly mainly in freshwater lakes rather than the ocean. In a preprint, an astronomer describes for the first time how one could search for quantum communication transmissions sent by ETI using existing telescope and receiver technology. He also provides arguments for why future searches of SETI should also target interstellar quantum communications. COVID-19 pandemic: Scientists report that patients who consistently met scientific guidelines of 150+ min/week exercise or similar physical activity had a smaller risk of hospitalisation and death due to COVID-19, even when considering likely risk factors such as elevated BMI. 14 April – Astronomers report that the supermassive black hole M87*, first, and to date, the only black hole to be imaged, will be further studied by many observatories from around the world and present results of simultaneous observations and their subsequent analysis.
15 April COVID-19 pandemic: The CDC, according to numerous media sources, reports that there were 5,800 COVID-19 breakthrough infections, and 74 deaths, in people fully vaccinated for the COVID-19 virus. On 21 April, scientists report that in a cohort of 417 vaccinated persons 2 women had vaccine breakthrough infections and identify their variants' viral mutations. Scientists report the creation, for the first time, of human-monkey hybrid embryos. Biologists report that an estimated 2.5 billion adult Tyrannosaurus rex dinosaurs roamed the Earth over the 2.4 million years of their existence. A study assesses that only 3% of the planet's terrestrial surface is ecologically and faunally "intact", with low human footprint and healthy populations of native animal species. Researchers demonstrate the whitest ever paint formulation, which reflects up to 98.1% of sunlight and could be used in place of air conditioners. 16 April – Scientists report that in the case of Alaskan forests, such boreal forests recovered from wildfires by shifting to a deciduous-coniferous mix, which could offset the carbon emitted during the fires. 17 April – New Horizons reaches a distance of 50 astronomical units (AU) from the Sun, while remaining fully operational. 19 April – NASA's Ingenuity helicopter, part of the Mars 2020 mission, performs the first powered aircraft flight in history not to take place on earth. The test location is named "Wright Brothers Field". 20 April Perseverance performs a test of its MOXIE instrument to convert carbon dioxide into oxygen for the first time on Mars. The Ivanti Pulse Connect Secure data breach of unauthorized access to the networks of high-value targets since at least June 2020 via across the U.S. and some E.U. nations due to their use of vulnerable, proprietary software is reported. Scientists show that a class of warp drives that are slower than light, could control the rate of time within the spaceship and are sourced from positive energy could in principle possibly be constructed based on known physical principles. Furthermore, they provide a new argument "why superluminal warp drive solutions may always violate weak energy conditions" and that the concept proposed in a study published in March "likely forms a new class of warp drive spacetimes". 23 April A malaria vaccine with 77% efficacy after 1 year – and first to meet the WHO's goal of 75% efficacy – is reported by the University of Oxford. Scientists report that of ~39 million groundwater wells 6-20% are at high risk of running dry if local groundwater levels decline by a few meters, or – as with many areas and possibly more than half of major aquifers – continue to decline. 27 April – Astronomers report the discovery of TOI-1431b, an "ultra-hot Jupiter" with a dayside temperature of ~3,000K (2,700 °C), making it one of the hottest exoplanets found to date. 29 April – The first, core module of the Chinese Tiangong space station, Tianhe, is placed in low Earth orbit. It is one of three permanent modules intended to be fully assembled in 2022 for a designed lifespan of 10–15 years, is 16.6 m in size and could host three astronaut scientists.
May
1 May A study that follows up on the randomized Abecedarian Early Intervention Project shows that 5 years of cognitively and linguistically stimulating center-based care starting between 3 and 21 weeks of age can result in significant changes in midlife brain structure in males. A meta-analysis of randomized trials suggests that lowering blood pressure at normal or high-normal blood pressure ranges is effective for prevention of major cardiovascular disease. 4 May Genetic signatures linked to extreme longevity in humans are identified by researchers and include genes for efficient DNA repair. A study assesses benefits of fast action to reduce methane emissions when compared to slower climate change mitigation of this form. On 6 May a U.N. report assesses benefits and costs of rapidly mitigating methane emissions. 5 May – Scientists report that Mediterranean diets protect against memory decline and mediotemporal atrophy such as in Alzheimer's by decreasing amyloidosis and tau-pathology. 6 May Researchers find that China's CO2 emissions surpassed that of all OECD countries combined for the first time in 2019. On 20 May China's CO2 emissions are found to be 9% higher than pre-COVID-19-pandemic levels in 2021-Q1 with CO2 emissions from fossil fuels and cement production having grown by 14.5% compared to 2020. Researchers report that bees were successfully trained to detect COVID-19 infections via samples. Researchers publish the first in-depth study of Web browser tab interfaces in over a decade and provide UI design considerations. 7 May Operation of the U.S. Colonial Pipeline is interrupted by a ransomware cyber intrusion. Researchers address a key problem of perovskite solar cells by increasing their stability and long-term reliability with a form of "molecular glue". Two studies complement research published September 2020 by quantum-entangling two mechanical oscillators. 10 May – A pan-coronavirus mRNA nanoparticle vaccine with activity against all major SARS-CoV-2 variants is described in Nature, showing potent effect in macaques. 11 May NASA reports on the continuous measurement, for the first time, of the density of material in interstellar space by the Voyager 1 space probe and the detection of interstellar sounds of vibrations of dense interstellar plasma. A new record for the smallest single-chip system is achieved, occupying a total volume of less than 0.1 mm3. Scientists estimate, with higher resolution data, that land-use change has affected 17% of land in 1960–2019, or when considering multiple change events 32%, "around four times" previous estimates and investigate its drivers.