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4.6 billion years ago: Formation of Earth

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4.6 billion years ago: Formation of Earth

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Earth forms from cosmic dust and debris. The early planet is a molten ball of rock with no solid crust, atmosphere, or water. This marks the beginning of our planet's incredible geological story that we can read through rock layers and fossils.

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4.4 billion years ago: First Solid Rocks Form

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4.4 billion years ago: First Solid Rocks Form

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As Earth cools, the first solid rocks begin to form. These igneous rocks create the foundation for future rock layers. Understanding how igneous rocks form helps us interpret Earth's history when we find them in rock sequences.

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4.0 billion years ago: The Hydrosphere Begins

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4.0 billion years ago: The Hydrosphere Begins

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Water vapor in the atmosphere condenses and falls as rain, creating the first oceans. This marks the beginning of Earth's hydrosphere - all the water on our planet including oceans, rivers, lakes, and groundwater. Water becomes crucial for life and rock formation.

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3.8 billion years ago: First Sedimentary Rocks

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3.8 billion years ago: First Sedimentary Rocks

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Erosion and weathering create the first sedimentary rocks as materials settle in layers underwater. The Law of Superposition tells us that in undisturbed rock layers, the oldest layers are at the bottom and youngest at the top.

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3.5 billion years ago: Earliest Fossil Evidence

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3.5 billion years ago: Earliest Fossil Evidence

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The oldest known fossils appear - microscopic organisms called stromatolites. These fossils provide evidence of early life and help scientists understand what Earth was like billions of years ago. Fossils become our 'time machines' to the past.

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540 million years ago: Cambrian Explosion

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540 million years ago: Cambrian Explosion

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A rapid diversification of life creates many new fossil types. Index fossils from this time, like trilobites, help scientists determine the age of rock layers. When we find trilobite fossils, we know those rocks are from the Cambrian period.

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400 million years ago: Plants Colonize Land

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400 million years ago: Plants Colonize Land

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The first plants move from water to land, leaving fossil evidence in rock layers. Plant fossils show how life expanded from the hydrosphere to terrestrial environments, changing Earth's surface and atmosphere forever.

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The largest mass extinction in Earth's history occurs. Rock layers from this time show a dramatic change in fossil types. This event demonstrates how catastrophic changes are preserved in the geological record.

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200 million years ago: Age of Dinosaurs Begins

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200 million years ago: Age of Dinosaurs Begins

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Dinosaur fossils first appear in rock layers. These index fossils help scientists identify Mesozoic Era rocks. Dinosaur fossils are found in sedimentary rocks that formed in ancient river systems and coastal environments.

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65 million years ago: Dinosaur Extinction

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65 million years ago: Dinosaur Extinction

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A dramatic change in fossil types marks the end of the dinosaurs. Rock layers show evidence of an asteroid impact. Above this layer, we find different fossils, showing how Earth's life forms changed over time.

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Today, scientists use the Law of Superposition, index fossils, and understanding of the hydrosphere to interpret Earth's 4.6-billion-year history. Every rock layer and fossil tells part of our planet's amazing story.