1. Aliens
   Water
2. Plants
   Animal life

Finding evidence of water on Mars was something that became a significant discovery in our modern history. While evidence that there had been water there was found, it's still unclear on whether or not it can still be found on the planet. However, it could be the key to unlocking history or secrets behind the red planet.

1. A disagreement with Hitler
   A kidnapping of an American in Europe
2. An attack from Japan
   An assassination

An attack on the United States naval base in Pearl Harbor by Japan was the reason the United States became involved in World War II. This came two years into the war, which began in 1939. In the four years that followed, the United States gained victory as part of the Allied powers.

1. Archean Eon
   Proterozoic Eon
2. Hadean Eon
   Phanerozoic Eon

The Phanerozoic Eon is the eon in which we are living right now. Surprisingly, Pangea, the supercontinent of our past, both formed and broke apart within this current eon.

1. An arthropod
   Bacteria
2. A plant
   A dinosaur

Trilobites were bug-like creatures that were found all over the Earth during the Cambrian period. They were most commonly found in the water, not far from the shore. This time period would have been a bug lover's dream!

1. Expanding
   Disappearing
2. Turning into a large black hole
   Getting hotter

In the theory of how the Big Bang started the universe, it is thought that it started off with everything in one place, and it is now endlessly expanding. The more the universe expanded, the more it began to cool off and allow organisms to sprout.

1. Wolf
   Deer
2. Koala
   Polar bear

A trip to the Tower of London nowadays wouldn't be very out of the ordinary. But during the reign of King Henry III, his pet polar bear was kept inside of the tower and allowed to go into the water as well. The bear was a gift from King Haakon of Norway.

1. Argentinosaurus
   Tyrannosaurus Rex
2. Triceratops
   Spinosaurus

The Argentinosaurus would be one that many in the world would fear if they were still alive nowadays. Their estimated weight was around 100 tons, but it is even less than the weight of a blue whale.

1. Phanerozoic Eon
   Proterozoic Eon
2. Archean Eon
   Hadean Eon

There are four eons in the Earth's very long history. The Archean Eon brought on some of the first life to emerge on Earth. Prokaryotes are organisms that have been traced back to this period, with many others living at this time as well.

1. Homo Habilis
   Neanderthals
2. Homo Sapien
   Homo Erectus

Homo erectus showed the first use of fire of the many early human ancestors. There is even evidence to suggest that Homo erectus was one of the first to cook food, helping with evolution over the years.

1. Envisat
   Aqua
2. Mir
   Sputnik 1

Sputnik 1 was the Russian satellite that first went into orbit. Unlike satellites such as the International Space Station, Sputnik 1 was extremely small, although that's not what the country had hoped for.

1. Sumer
   Tenochtitlan
2. Norte Chico
   Timbuktu

The city of Sumer was the first of its kind. It's in Mesopotamia and became one of the oldest civilizations in history. Sumerians had prime real estate, as their agricultural base was located between two major rivers. Because of the reliable irrigation, the city of Sumer had the crops to support large populations as they pursued arts and language organizationally.

1. Piano
   Guitar
2. Harmonica
   Bagpipes

The piano that we know today first got its start in the late 1600s. Over the years, the piano saw improvements from other revolutionary individuals. It's thanks to Bartolomeo Cristofori that we now get to enjoy the sweet sounds of the piano.

1. Natural disaster
   Political turmoil
2. Disease
   Economy

The Aztec civilization was affected severely by diseases that were brought by the Spaniards. One disease that had a devastating effect on the Aztec people was smallpox, which contributed to their downfall.

1. Poisoned themselves
   Communicated with other emperors
2. Volunteered to help someone out
   Designed a piece of clothing

Most wouldn't think that a emperor would want to poison themselves, but it was a common practice in ancient Rome. The thought process behind it was that if they poisoned themselves a little bit each day, they would become immune to it.

1. Cenozoic Era
   Renaissance Era
2. Jacobean Era
   Mesozoic Era

The dinosaurs were around for a very long time on Earth. Throughout their over 100 million year history on the planet, they evolved and reproduced until their extinction. Did you know that a pterodactyl is not actually a dinosaur? It was a reptile!

1. News is consumed through more digital platforms.
   News is available through many more different channels than before.
2. News travels almost instantly.
   All of the above

The news has been revolutionized since the rapid growth of technology. Almost everyone has a phone with them that allows them to find out something that happened mere seconds earlier at the click of the button. The world has come a long way since the Pony Express!

1. The United Postal Service
   West Mail
2. The Pony Express
   Cross Country Mail

The Pony Express was an important part of communication in the American West. The service could take a letter across the country for you, but the travel made it a slow alternative. At the time, it was hard to do anything must faster.

1. Karl Marx
   Voltaire
2. Socrates
   Confucius

Socrates, another important philosopher, was Plato's teacher. Plato then became a teacher himself, spreading what he learned to young philosophers such as Aristotle. The three are regarded as some of the greatest philosophers in history.

1. Square dancing
   Technology
2. Politics
   Christmas tree

The Christmas tree rose to fame in the Victorian era, after Prince Albert and Queen Victoria set one up in their home. As with many things that the queen did and wore, it became an overnight sensation.

1. London
   Paris
2. Florence
   Athens

Florence, Italy, was where the Renaissance truly got its start and became famous for the art that came out of it. However, much more was affected by the time period. Much of the thinking in the world, as well as the political climate, changed during that period.

1. Live birth
   Eggs
2. Virgin birth
   Born as embryos

Dinosaurs gave birth quite similar to how birds give birth today — laying an egg and hatching it. In fact, birds are descendants of these ancient creatures, which can explain a bit about why they both share the same birthing practices.

1. Planets
   Dinosaurs
2. Humans
   Pyramids

The Hadeon Eon is an important one for our solar system. The planets were formed during this time, as well as our moon. Did you know that the moon was formed by many rocks coming together to form one bigger body?

1. South America
   Europe
2. Australia
   Asia

The Isthmus of Panama was formed about 3 million years ago. But it's formation has changed the world and the climate of the Earth. Before this narrow strip of land emerged from the water, the Pacific Ocean separated North and South America.. The Panama Canal cuts through the Isthmus of Panama, allowing vessels to pass from the Atlantic to the Pacific.

1. Europe
   North America
2. Australia
   Africa

Everyone knows Pangea, but after this super continent, there were many more to come. Baltica was one of them and it was a smaller continent during its time. Nowadays, you can get a taste of the ancient Baltica in Europe and Asia.

1. Bacteria
   The Sun
2. The Big Bang
   Asteroids

Asteroids are thought to be the origin of the water on Earth, as they carry many of the same chemicals, as well as carry ice. Larger asteroids would have been very capable of putting huge amounts of water on the surface of Earth.

1. Health care
   Tools
2. Writing utensils
   Water purification methods

An early ancestor of humans, Homo habilis knew how to create simple tools to make their lives a little easier. The tools were often used for tasks like carving. Many of these tools have been preserved since their discovery.

1. Airplanes
   Cannons
2. Boats
   Animals

Planes were used heavily for the first time in this worldwide conflict. Each country developed its own planes that would fight from above by taking out enemy airplanes in the air or taking out people on the ground.

1. Drawings
   Email
2. Google Docs
   Cameras

Everyone has a camera in their pocket today. With the popularity of phones and even digital cameras, the world is constantly being documented. The people of the future might find that they have a much easier time to see how we lived in our day.

1. Generation II
   Millennials
2. Baby boomers
   Generation Z

Baby boomers are a unique generation of people born just after the end of World War II. This was a time where a large number of babies were being born, creating a very large generation of kids.

1. LGBTQ+ rights
   Environmental issues
2. Health care
   All of the above

Although these three categories only scratch the surface of the many issues in the world, they have become very important in today's society. There's always more we can do to make progress!

1. Neil Armstrong
   John Glenn
2. Gene Cernan
   Wally Schirra

Neil Armstrong will forever go down in history as the first man to set foot on the moon during the Apollo 11 mission. It's something many of us could only dream of doing. He did it alongside his fellow astronaut, Buzz Aldrin, while the mission's third astronaut, Michael Collins, circled the moon in the Command Module until Armstrong and Aldrin rejoined him before heading back to Earth.

1. A telephone
   An implant
2. A vaccination
   A computer

This is not to be confused with the personal computer, which came about at a much later date. But the first computers largely dealt with numbers and weren't exactly the same as the computers we know today.

1. Hipparchus
   Aristotle
2. Galen
   Plato

The stars were here long before the human race was, and new stars are constantly being formed. The first to be witnessed and recorded was when Hipparchus, an astronomer, came across one.

1. Jewish people
   Germans
2. Amish people
   Mennonites

The Star of David is a Jewish symbol which the Nazis used to identify Jews during World War II. Over time, these identifiers changed and a number of different symbols and pieces were worn instead.

1. Snowball Earth
   Flourishing Earth
2. Tropical Earth
   Ancient Earth

Snowball Earth is a term given to the Earth during the Proterozoic Eon due to its frozen state. In fact, if we had been alive at this time, you wouldn't have had to be living at the poles to be living where the snow was. Ice covered the entire Earth.