Life Changed Over Time
Recognise that living things have changed over time and that fossils provide information about organisms that inhabited the Earth millions of years ago
What a learner can do afterwards
- State that living things have changed (evolved) over millions of years
- Describe how fossils form and what information they provide about the past
- Compare a fossil organism with a modern relative, noting similarities and differences
1 · Read
Long ago, Earth looked different. The plants and animals alive today are not exactly like the ones that lived millions of years ago. Little by little, living things have evolved, generation after generation.
Fossils of small dinosaurs from millions of years ago show feathers and hollow bones, just like the birds flying around today. Scientists compare these old fossils with living birds and see how one group slowly changed into the other. A fossil is the shape of a living thing from long ago, kept in rock. After an animal dies, its soft parts rot away. Its hard bones and teeth can get buried in mud. Over a very long time, minerals turn them to rock.
Fossils sit in rock layers, like pages stacked in a book. Where layers are still stacked in the order they formed, deeper layers are usually older, so scientists can often figure out which changes happened first.
Fossils record how living things have slowly changed over millions of years, connecting animals and plants today to their ancient relatives.
More to read
Evolutionary History: The Timeline of Life: Crash Course Biology #16
Life has been changing for billions of years, far longer than humans have existed. Tiny cells came first, then bigger cells, then animals and plants. Each big leap shows up in fossils in order, from old rocks to young rocks. The timeline only runs one way.
Fossils let us compare then and now. Pick an ancient fossil and its closest living relative. List what stayed the same and what changed. Every difference marks evolution at work across millions of years.
Introducing Darwin and natural selection
Charles Darwin noticed that no two living things are exactly alike. Some differences help their owners survive and raise young. Those helpful traits get passed on, while harmful ones fade. Over millions of years, this slow filter can reshape a whole species. Darwin called it natural selection.
Fossils back him up. Old sloths, birds, and even young animals show halfway traits that link past and present. Change piles upon change until new forms appear. That is how life on Earth became so varied.
What Is the Biosphere?
The biosphere is the part of Earth where life exists, from deep seas to high skies. It has lasted for billions of years, but its members keep changing. Dinosaurs once filled it, and mammals fill much of it now. The stage stays, while the actors change.
Fossils are snapshots of past casts. Compare a fossil with a modern animal that lives the same way. Note the matching bones and the new twists.
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2 · Watch
En anglaisTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
24 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.