Ebola was the biggest public-health emergency in 2015, and, this year, another virus known as Zika entered our lexicon.
It was also a year for scientific firsts, including an unmanned spacecraft named Juno successfully beginning to orbit the planet Jupiter.
The year began with governments around the world, including Australia, issuing travel warnings to pregnant women about going to Zika-infected countries.
Those countries ranged across South America, the Caribbean, Central America, Africa and the Pacific Islands.
The disease is transmitted by a mosquito that has bitten an infected person.
Although death from the virus is rare, it has been linked with thousands of babies being born with underdeveloped brains.
Brazil's health ministry confirmed the Zika virus is linked to a foetal deformation known as microcephaly, (my-kro-SEF-uh-lee) where infants are born with smaller brains.
The head of the World Health Organisation, Margaret Chan, described the development as worrying.
"The explosive threat of the Zika virus to new geographical areas with little population immunity is another cause for concern, especially given the possible link between infection during pregnancy and babies born with small heads."
For many people, learning about chemistry ended after leaving high school.
But this year, there was renewed interest in the periodic table, which arranges the chemical elements in order of their atomic numbers, after scientists discovered four new elements.
Joining the table are nihonium (atomic number 113), moscovium (115), tennessine (117) and oganesson (118).
Unlike most of the elements on the table, they are unstable and only exist in experiments in laboratories.
Just as chemists were celebrating new discoveries, physicists were excited, too, about the detection of faint ripples in the fabric of spacetime called gravitational waves for the first time.
It confirmed a prediction by Albert Einstein in 1916.
Gravitational waves are created whenever there is a huge event in the universe -- for example, when black holes collide.
Astrophysicist Katie Mack explained it opens up new ways of understanding the universe.
"We'll be able to see some of the most violent events in the universe. Two black holes colliding and merging. Possibly we'll be able to see neutron stars colliding and merging. Super massive black holes, when they merge together, get bigger, and that's part of what happens when galaxies come together and form new galaxies, so this is a way that we're going to be able to really study the formation of galaxies, the build-up of mass in the universe and how black holes act. We'll learn something about what kind of black holes are out there, how many of different masses, which tells us something about stars and how stars form and die and everything."
By the middle of the year, it was space nerds celebrating the successful entry of an unmanned spacecraft into Jupiter's orbit.
The probe, known as Juno and powered only by the sun, took almost five years to reach the solar system's largest planet.
Juno is expected to send information back to Earth while studying what lies beneath Jupiter's thick clouds and mapping the planet's enormous magnetic fields.
Each orbit it takes around Jupiter will last 14 days.
It will also look for evidence Jupiter has a dense inner core and measure how much water is in the planet's atmosphere.
Lead scientist Scott Bolton said the mission will help scientists understand the formation of the solar system.
"You know, what Juno is really about is learning about the recipe for how solar systems are made. Scientists don't really understand how the planets are made. We know, after the sun formed, something happened and we were able to form Jupiter. It took up more than half of the material that was left over. And it's a little bit different than the sun, and we don't completely understand that, and that's really the first step in that recipe."
Other scientific breakthroughs of note included the birth of the world's first so-called "three-person baby."
Doctors in the United States revealed a boy had been conceived through a new technique known as "three-person fertility."
That is, the child not only has DNA from his parents, but also some from a donor.
The step was taken to ensure the baby would not inherit a genetic condition his mother carries in her genes.
Some medical analysts are hailing it as a new era in medicine and in treating rare genetic conditions.
And perhaps one of the most significant agreements in recent history was ratified by almost 200 countries -- including Australia -- bringing it into effect globally.
The Paris climate deal, reached in the French capital in 2015, lays out a global plan to take steps aimed at limiting climate change.
Fiji was the first country to join the Paris Agreement.
Prime Minister Voreqe Bainimarama explained the urgency of ratifying the pact.
"My country, along with other small island nations, is on the front lines of climate impacts. The rapid entry into force and implementation of the Paris Agreement is critical for our national survival. We have a responsibility to our people and to all the world's people to protect them from rising seas, from powerful storms, from hurricanes and cyclones, from crippling floods, devastating droughts and higher temperatures."
