Fossils and Geological Time
Fossils are preserved remains that reveal Earth's history.
About this topic
Fossils are preserved remains or traces of ancient organisms, most commonly formed when hard parts are buried in sediment and mineralised. Rock layers (strata) record time, with older layers generally deeper. Radiometric dating, using isotopes like uranium-238 and carbon-14, gives ages in years.
The geological time scale divides Earth's 4.6-billion-year history into eons, eras and periods. The fossil record is incomplete, but it shows life progressing from simple to complex, and index fossils help date rocks.
Fossils can be formed in other ways: amber traps insects, ice preserves mammoths, and trace fossils such as footprints record behaviour. Radiometric dating uses decay of unstable isotopes: carbon-14, with a half-life of about 5,730 years, dates things up to about 50,000 years, while uranium dating works on rocks millions of years old. After one half-life, half the isotope remains.
Index fossils, from species that lived briefly but were widespread, help match rock layers in different places. The geological time scale divides history into eons, eras and periods, such as the Jurassic. If the whole of Earth history were a 24 hour day, humans would appear in the last few seconds. Do not confuse relative dating, which only orders layers, with absolute dating, which gives numeric ages.
Key ideas
- Sedimentary layers
- Radiometric dating
- Index fossils
Quick check
Use cases: where Fossils and Geological Time helps
- Homework: review the key idea behind Fossils and Geological Time before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Fossils and Geological Time without notes.
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Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Fossils and Geological Time?
Fossils are preserved remains that reveal Earth's history.
What will I learn in Fossils and Geological Time?
Sedimentary layers. Radiometric dating. Index fossils.
Is Fossils and Geological Time part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Fossils and Geological Time lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Fossils and Geological Time?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
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