Covid-19 dominated science coverage in 2020, and rightly so. The world grappled with how to combat the SARS-CoV-2 virus, learning about how it spread (whether it was on surfaces, via droplets or being airborne) and how it affected the human body (from immunity to symptoms like loss of smell.) But scientific endeavors in other fields, whether affected directly by the pandemic or indirectly by public health measures, didn’t come to a complete halt because of SARS-CoV-2. In incredible advances, researchers used three new tools for making discoveries about the sun, discovered that dinosaurs got cancer and published a study on a discovery in a Mexican cave that changes the timeline of humans’ arrival to the Americas. But none of those moments made this list of the biggest science stories of the year. It’s a subjective round-up, of course, but one compiled by our editors after much thought and debate. Presenting the key innovations, studies and discoveries that made 2020 an unforgettable year in science:

Companies Develop Covid-19 Vaccines in Record Time

First Batch of Pfizer-BioNTech Vaccine
A vile of the Pfizer-BioNTech vaccine against COVID-19 that was delivered to Arrowhead Regional Medical Center in Colton, California
(Irfan Khan / Los Angeles Times via Getty Images)

Since the first case of Covid-19 was reported in China late last year, more than 802 million cases and more than 1.7 million deaths have been confirmed around the world. In the United States, more than 19 million patients have tested positive for the disease and more than 338,000 of them have died. While the disease continues to spread and cause death, help is in sight thanks to the record-setting effort to develop vaccines. In less than a year, Moderna and Pfizer, in cooperation with BioNTech, created the first messenger RNA (mRNA) vaccines ever to protect against Covid-19. An mRNA vaccine contains a synthetic version of RNA that tricks the immune system into thinking a virus is present so that it will make antibodies designed to fight the virus. This is different from a traditional vaccine, which is made of small amounts of an existing virus. The previous record for vaccine development was for mumps, which took four years in the 1960s, but Moderna started working on a vaccine in January and Pfizer and BioNTech began working together in March. By July, both companies began late stage trials, each with roughly 30,000 participants. In November, the companies declared their vaccines were more than 90 percent effective. By mid-December, the FDA approved both vaccines for use in the United States. National Institute of Allergy and Infectious Diseases director Anthony Fauci hailed the accomplishments as a “triumph.” Now comes the complicated, months-long process of distributing the vaccines to the public.

NASA Snags Its First Asteroid Sample

Artist’s conception of NASA’s OSIRIS-REx spacecraft collecting a sample from the asteroid Bennu
(NASA/Goddard/University of Arizona)

In October, the NASA spacecraft OSIRIS-Rex reached out and grabbed rocks from a 4.5-billion-year-old asteroid named Bennu. The mission, which took place more than 200 million miles away from Earth, marked the first time the space agency reached out and touched an asteroid. The craft was supposed to land on the mass, but the surface proved too rocky, so the team behind the effort pivoted to using a robotic arm to snatch a sample. The smashing success almost worked too well; the collection module vacuumed up so much rock that a vital flap couldn’t close. Scientists abandoned their plans to measure the sample and took days to implement an effort to successfully store the rocks. The sample should arrive on Earth three years from now. Experts think it may contain water and prebiotic material, the building block of life. Such evidence might offer clues about how life on Earth started.

Habitats Burn During One of the Hottest Years on Record

LNU Lightning Complex Fire
Flames surround Lake Berryessa during the LNU Lightning Complex fire in Napa, California on August 19, 2020.
( Josh Edelson/AFP via Getty Images)

As of the writing of this list, 2020 is in competition with 2016 to be the hottest year ever recorded. This possible peak continues a dangerous trend, with the ten hottest years ever documented all occurring since 2005. Perhaps no illustration of the effects of climate change this year was more dramatic than the preponderance of massive wildfires. Millions of acres in Australia, which was set up for disaster as 2019 marked its hottest and driest year on record, burned from last October into January 2020. Thousands of Australians fled their homes, and many animals died or scurried from their threatened habitats. In Brazil, fires ravaged the Pantanal, the world’s largest tropical wetland, from July through October. Roughly a quarter of the ecosystem , which is larger in area than Greece, burned. Residents and animals abandoned their homes for safety, unsure of what would remain when they returned. In the United States, California recorded its worst fire season ever, with more than 3 million acres destroyed. Massive fires have dominated the state recently, with seven of the most destructive burns taking place in the last five years. Hot, dry summers, due in part to climate change, have set the region up for longer, more volatile fire seasons.

Scientists Discover Signs of Possible Life on Venus, or Maybe Not

Venus is a world of intense heat, crushing atmospheric pressure and clouds of corrosive acid.

In September, astronomers published a pair of papers saying they detected a gas called phosphine on Venus. They said the discovery, which was made using telescopes in Hawaii and Chile, suggested a living source for the gas because other conditions on the planet couldn’t lead to phosphine formation. News outlets from The New York Times to National Geographic picked up the story, while reporting that some experts were skeptical of the finding. In October, three independent follow-up studies failed to find the gas on Venus. One of the studies used new data, and the other two used the initial team’s original data. In November, the original team revised their figures and said that phosphine levels were seven times lower than their initial estimate. As the debate about the presence of the gas continues, the story is important not just because of the correction, but because of what it shows: Science is a process in which findings are presented and then opened up to scrutiny and revision.

Microplastics Invade the Furthest Reaches of the Globe

Plastic Debris
Plastic debris covers the beach of the Costa del Este neighborhood in Panama City.
(Luis Acosta/AFP via Getty Images)

News that microplastics have spread into many of the earth’s habitats is nothing new, but this year, scientists published several studies showing that the amount is much greater than previously thought and the reach is much further than previously documented. In April, researchers documented microplastics in Antarctic sea ice for the first time. In June, a study published in Science estimated that 1000 tons of airborne plastic debris rains down on national parks and remote stretches of wilderness in the United States. The country’s estimated contribution of plastic waste to the oceans was shown to be double what was previously thought. And in October, scientists published a study estimating that 15.8 million tons of microplastic are embedded in the Earth’s seafloor—or a lot more than is floating at the ocean’s surface. Not only the planet’s lowest points have been trashed; scientists published a study in November that found microplastics in every sample collected from the slopes of Mount Everest, with one such sample collected at 27,690 feet above sea level. Plastic debris has infiltrated Earth’s water, air and the living tissues of so many creatures, including humans. What scientists don’t know yet, is all of the ways the pollution affects us.

Three Different Early Humans May Have Lived Together in South Africa

Drimolen Fossils
The Drimolen excavations and excavated fossils
(Andy Herries)

Despite being widely discredited in modern archaeology, orthogenesis—the theory that species evolve in neat succession, with new species replacing extinct species without much overlap—still looms large in the public understanding of human evolution. Researchers now say that evolution may have looked more like a scene first described in April this year, where three different species of possible human ancestors lived together in the same ancient cave in South Africa’s Cradle of Humanity. Tucked away in a roofless, amphitheater-like dwelling known as the Drimolen Paleocave System, skull fragments from Australopithecus africanus, Paranthropus robustus and Homo erectus were found to date back to 1.95 million years ago. This time period would mark the end of Australopithecus’s reign and the early beginnings of Paranthropus’s short-lived existence. Remarkably, the find could push back H. erectus’s origins by about 100,000 years; a cranium fragment scientists discovered might be the earliest fossil evidence of the species. Collapsed layers of fossil-packed sediment make precise dating tricky, but this study provides new evidence of multi-species hominin coexistence in a new geographic location, suggesting our ancestors were much more diverse than previously thought.

New AI Tool Cracks a Decades-Old Problem in Biology

Proteins are tiny molecular structures that make life on Earth go ’round. All proteins start out as a chain of chemical compounds called amino acids. Those chains then fold, twist and turn over and over again into perplexing tangles that eventually develop a three-dimensional shape. A protein’s shape defines what it can and can’t do—enter and alter certain cells, for example. When scientists can determine those 3-D shapes, the knowledge helps them understand how viruses spread, crack genetic codes and breakdown cellular infrastructure. Researchers have been searching for ways to crack the code of protein structures for 50 years. Scientists using existing technology require years of trial and error efforts to figure out a protein’s shape. This year, Google’s artificial intelligence company DeepMind debuted a deep-learning tool called AlphaFold that can determine a protein’s structure in a matter of days. The potential applications and breakthroughs this technology offers are numerous, including quicker and more advanced drug discovery. As one researcher described the find to Nature magazine, “It’s a breakthrough of the first order, certainly one of the most significant scientific results of my lifetime.”

The United States Is On Track to Eliminate Cervical Cancer

HPV Vaccine
A pediatrician gives an HPV vaccination to a 13-year-old girl in Miami, Florida.
( Joe Raedle/Getty Images)

In a year plagued by a different kind of virus, good news is on the horizon regarding a form of cervical cancer associated with the human papillomavirus (HPV). Even without increased vaccination or screening, the United States is on pace to eliminate cervical cancer within the next 20 to 30 years, according to report released this year. When pap smears were widely introduced and regularly implemented at a global scale nearly a half-century ago, cervical cancer deaths began to drop. A vaccine introduced in 2006 prevented HPV infections that lead to cervical cancer. If medical professionals ramp up current vaccination and screening efforts, cervical cancer could be eliminated even sooner than expected, according to statistical models used in the study.

The United States Watched Washington Scientists Battle Invasive ‘Murder Hornets’

Murder Hornet
The Asian giant hornet, the world’s largest hornet, was sighted in North America for the first time.
(Washington State Dept. of Agriculture)

With a nickname like “murder hornets,” Asian giant hornets were hard to ignore, even though researchers spotted only a few at first. Asian giant hornets (Vespa mandarinia) decimate honey bee populations fairly efficiently (hence their nickname) and their sting is far mightier than any common bee found in North America. But after the New York Times published an article about scientists’ efforts to get ahead of the species before they settled for good in Washington state and British Columbia, the internet was abuzz with interest. Though four hornets had been spotted since fall 2019, it wasn’t until early October that the first live hornet was captured. By mid-October, entomologists found, isolated and incapacitated a nest that contained more than 500 “murder hornets,” including 200 queens. Though scientists may have arrived there in the nick of time, it’s impossible to know whether some of those queens mated and set off to start their own colonies, so a team is still on the lookout for the stinging beasts. All in all, the internet hysteria was exaggerated—and not exactly harmless either. Search engine inquiries about pesticides jumped, and common, oft-overlooked pollinators prompted panicked calls to local environmental agencies. One good thing to come out of the story? Folks learned a bit about the importance of controlling invasive species.

In 50 Years, Humans Have Decimated Two-Thirds of the World’s Wildlife

Leatherback Sea Turtle
A leatherback sea turtle hatchling, an endangered species, crawls to the ocean.
(Mark Conlin/VW PICS/UIG via Getty Image)

Since 1970, 4,392 mammals, amphibians, birds, fish and reptile species’ population sizes declined by 68 percent, according to a World Wildlife Fund report released this year. Animals living in Latin America and the Caribbean took the biggest hit; their population sizes decreased by 94 percent. Habitat destruction is cited as the leading cause of these massive losses. The United Nations’ Global Biodiversity Outlook report produced similarly grim results. The document took inventory of 196 countries committed to recovering biodiversity as determined by the 2010 Aichi Biodiversity Targets. As dictated by the Aichi agreement’s ten-year plan, countries were to achieve certain recovery milestones like preventing the spread of invasive species and conserving protected areas. Most of the goals were not achieved or only partially met. Furthermore, the reports warned that pandemics, like the one the world is currently facing, could become more common if humans’ “broken” relationship with the natural world is not mended. In a statement, U.N. Convention of Biological Diversity executive secretary Elizabeth Maruma Mrema said, “the more humanity exploits nature in unsustainable ways and undermines its contributions to people, the more we undermine our own wellbeing, security and prosperity.”