Earth is the only planet we know of that can support life as we know it. It’s been around for about 4.5 billion years, but its history goes back much further than that—before humans were even around to start recording things. So what happened during all those billions of years? We’re glad you asked! Here’s our brief (but not too brief) primer on how everything got started.
The Big Bang is the most widely accepted scientific explanation for the origin of our universe. It’s also one of the most exciting and fascinating ideas in all of science, because it tells us that our entire cosmos sprang into existence from an infinitesimally tiny speck of matter in an unimaginably hot and dense state. And this happened 13.8 billion years ago! When we talk about “the big bang,” what we mean is that space itself began expanding rapidly after this initial moment–and it continues to expand today at a rate of about one light-year every 5 minutes (that’s about 6 trillion miles per hour). The theory was first proposed by Belgian priest Georges Lemaître in 1927; he called it his “hypothesis.” But many people didn’t believe him at first, because they thought that exploding stars could only produce matter rather than create new space itself (which makes sense if you think about how explosions work).
The formation of the solar system is a complex process that took millions of years. The sun formed at the same time as its planets, but it’s been around much longer than any of them. In fact, it’s thought to be about 5 billion years old! The planets themselves were formed from gas and dust left over from when our galaxy was formed (about 13 billion years ago). These materials coalesced into balls that became larger as they accumulated more matter through gravity–this process is called accretion. Over time, these balls grew so big that they acquired enough gravity to pull in smaller objects around them; eventually they became small moons orbiting their respective planets’ surfaces. The orbits of these moons are elliptical rather than circular because they orbit around both their planet and another object: either another moon or one or more asteroids/comets nearby in space.
The Great Oxygenation Event(s) were a series of events that occurred around 2.4 billion years ago, during which oxygen in Earth’s atmosphere increased dramatically from 0% to about 21%. These events were caused by cyanobacteria, who are anaerobic and produce oxygen as a waste product when they photosynthesize. Before this time there was little or no free oxygen in Earth’s atmosphere; it was mostly nitrogen gas with trace amounts of other gases like carbon dioxide and methane (which are greenhouse gasses).
The first life on Earth was single-celled, and it appeared around 3.5 billion years ago. The first multicellular organisms appeared around 700 million years ago. The first animals appeared around 550 million years ago (although some scientists believe that this date could be pushed back even further). Land plants began to appear around 450 million years ago, but they did not become widespread until 350 million years later when they were able to colonize the land in large numbers as a result of an increase in atmospheric oxygen levels caused by photosynthetic activity by cyanobacteria (blue-green algae).
The Cambrian Explosion was a period of time from about 541 million years ago to 488 million years ago, when lifeforms began to rapidly diversify and evolve. It was during this time that most of the major groups of organisms appeared on Earth for the first time–including vertebrates (animals with backbones), arthropods (insects and spiders), mollusks (clams and snails), echinoderms (starfish), chordates (animals with spinal columns) and several others. The Cambrian Explosion lasted about 10 million years–a relatively short amount of time compared to other periods in Earth’s history. But it was also very important because it marked one of two major transitions in evolution. The first transition occurred when single-celled organisms developed into complex multicellular organisms like plants and animals; these were referred to as metazoans because they contained multiple “zoa” or living units within themselves rather than being just single cells like bacteria are today.* The second transition occurred during this period when simple invertebrate marine animals evolved into more complex ones like mollusks or arthropods like insects; these creatures eventually led to modern vertebrates such as humans who possess backbones made up mostly out carbon atoms rather than silicates found elsewhere throughout nature (like rocks).
You probably know that humans are the only species to use tools and build houses. You may also be aware that we are not the only animals that can communicate using language, but did you know that there are other apes that do so? Or some birds? It’s true! And this leads us to an interesting fact about our evolution: it took millions of years for humans to evolve into what they are today.
The history of Earth is pretty awesome and complicated. It’s a timeline from the Big Bang to humans, but it also includes events like the formation of our Solar System and the rise of life on this planet. We’ve come a long way from the Big Bang, but we’re still learning more every day. I hope this article has helped you see how our planet has evolved over time and will continue to do so in the future!