Geology
The word Geology comes from Ancient Greek. Ge (“earth”) and ology (“study of”). So based off the simple break down of the word, Geology is the study of the Earth. This includes the rocks that make up the earth along with the solid features around the globe that make up so many features. A person who studies the Earth is called a Geologist. Geologists, through studying the Earth, are able to make educated guess (hypothesis) of how old the Earth is, movement through plate tectonics, and past climates.
Some of these educated guesses include:
4.567 billion years ago: Solar system formation
4.54 billion years ago: Earth formation
4 billion years ago: First Life on Earth
3.5 billion years ago: Start of photosynthesis
2.3 billion years ago: Oxygenated atmosphere, First snowball Earth
730-635 million years ago: Second snowball Earth
541 million years ago: hard-bodied life, first abundant fossils, start of the Paleozoic
380 million years ago: First vertebrate land animals
250 million yeas ago: 90% of all land animals die, end of Paleozoic, beginning of Mesozoic
66 million years ago: Cretaceous-Paleogene extinction, Dinosaurs die, end of Mesozoic, beginning of Cenozoic
7 million years ago: First hominins appear
3.9 million years ago: direct ancestor to modern Homo sapiens appear
200 thousand years ago: First modern Homo sapiens appear in East Africa