The Earth was created approximately 4.6 billion years ago when a nearby star imploded and dust, rocks and gas in the solar system collided and, because the temperature was so high, the material was effectively glued together. Over time, more and more material (rocks and dust, mostly) collected together and they became larger and larger objects that ultimately made up a planet. Life began on Earth somewhere between 4.4 billion years ago (when water vapor first formed) and 2.7 billion years ago (where we have the first evidence of photosynthesis). Scientists are still working to understand exactly how the first life forms were formed, but most early life scientists agree that early life forms were most likely small, simply bacteria, containing a single cell. Each cell has within it a "code" that records what it is made of and the recipe for how to make itself again. Sometimes, this record got disturbed and the recipe wasn't exactly right, so instead of making 1 cell, the recipe made 2 cells that were joined. Through many "mistakes" in the recipe over time (something scientists now call evolution), single-celled organisms evolved into cooperative teams of cells that would replicate themselves. Almost every scientist believes that humans have evolved over billions of years through simple changes in the "recipe."

I have attached a diagram of the "Geologic Clock," which shows the relative time it took for all these changes to happen.

Geological_c lock