The big bang theory suggests that a "big bang" took place 13.7 billion years ago. It created the universe.
The atmosphere of early earth was primitive. It contained ammonia, methane, water vapor, carbon dioxide, and nitrogen gas. However, Cyanobacteria were able to withstand this harsh environment.
Cyanobacteria performed photosynthesis. The oxygen produced created the ozone layer.
The theory of plate tectonics suggests that today's continents were once a supercontinent known as Pangea. The movement of plate boundaries separated these continents and created mountains, volcanos, and faults, along with three rock types: igneous, metamorphic, and sedimentary. Evidence of fossils, glaciers, and rock support this theory.
The law of superposition supports the fossil record and geological timescale, which have allowed us to understand the history of Earth. It states that in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom.