Fossil Records: A Journey into the Past
Every fossil lived before our time. They’ve been untouched for centuries like frozen photographs. After we recover one, we piece together the geologic past with fossils.
Every fossil is like a puzzle piece that we link to the evolution of life.
By examining a simple imprint in rock, we understand “when”. Through rock superposition, we unveil ancient supercontinents and the time these life forms existed.
Fossils don’t exist for 88% of history
Only primitive life forms like bacteria and archaea lived in early Earth. It wasn’t until the Cambrian period that complex life finally began to thrive.
The Cambrian explosion marked a time that a wide array of life forms evolved. For example, we’ve uncovered fossils with shells or exoskeletons after the largest diversification of life in Earth’s history.
This means that for more than 88% of Earth’s history, complex life did not exist. That’s why we call this era in geologic history the Precambrian. It’s because it was before the Cambrian explosion where hard-shelled life emerged.
Fossils only come from sedimentary rocks
Sedimentary rocks are the only type of rocks that may contain fossils. If you see a rock with a fossil, you can automatically assume that it is a sedimentary rock.
This is because the process of formation for igneous and metamorphic rocks involve heat or pressure that fossils would be completely erased.
These are the rocks that can incorporate bones, shells, and exoskeletons from living organisms such as shells which are compacted sea creatures.
Piecing together the dinosaur fossil puzzle
Dinosaurs lived on the supercontinent of Pangea for over 160 million years. Plate tectonics was the mechanism that eventually tore continents apart.
We know this because we can find the same fossils on separate continents today. We see fossils records of the same land herbivores today on separate continents that couldn’t fly or swim.
The reason is because they lived on Pangea and over time it separated by continental drift. To this day, scientists have kept a thorough record documenting each fossil discovery.