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Course: Middle school biology - NGSS > Unit 8
Lesson 2: The fossil recordEarth's fossil record
Review your understanding of Earth's fossil record in this free article aligned to NGSS standards.
Key points
- Life has existed on Earth for billions of years. Evidence of life on Earth, and how it has changed over time, is found in the fossil record.
- The fossil record is made up of all the fossils that have been found, along with their relative ages. Scientists can look at patterns in the fossil record to understand the history of life on Earth.
- For example, the fossil record shows us that there has been an overall increase in the complexity of organisms over time. It also shows us that there has been an increase in organism diversity.
- The fossil record shows us when specific types of organisms appeared, went extinct, or changed.
- And, the fossil record shows us that there have been mass extinctions in Earth’s past. A mass extinction is when many species die off around the same time.
Want to join the conversation?
Why do fossils take so long to decay.(9 votes)
This is because they lived in the sea, where sand or mud could bury their remains quickly after they died. Once remains are buried under sediment, their decomposition slows down due to a lack of oxygen, giving enough time for fossilisation to occur.(23 votes)
- why do fossils take so long to decay(5 votes)
- This is because they lived in the sea, where sand or mud could bury their remains quickly after they died. Once remains are buried under sediment, their decomposition slows down due to a lack of oxygen, giving enough time for fossilisation to occur.(10 votes)
- How many mass extinctions have we had since Earth was created?(5 votes)
5, but we are living the 6(5 votes)
why do mass extinction happen?(3 votes)
Mass extinctions are caused by extreme changes. An example would be the asteroid that killed the dinosaurs. There have been 5 mass extinctions, some caused by extreme temperature changes, asteroid impacts that push so much ash into the atmosphere it blocks the sun for decades, and changes in atmospheric composition such as increases in CO2 and Oxygen.(8 votes)
How can fossils be preserved in sedimentary rock if it can break? what will happen?(3 votes)
Well they stay in good condition because the rocks take very long to fully harden, because of this and the fact that they are buried under the ground, they are preserved and then can be dug up later by let’s say humans. Now if the rock was to break when people would try and get it out then simply the fossil would break. Breaking is unlikely to happen due to how big these rocks can be, I mean think about it, they are underground for many many MANY MANY Years. So the sediment forms together and makes a HUGE rock.(6 votes)
- what does the fossils tell us(4 votes)
- They can give us clues to what old species may have looked like or their bone structures and even more, we can even tell how old these fossils are by using radiology, which also tells us how old the extinct species are, there is many things!(4 votes)
- Can you tell how long they have been there?(3 votes)
- yes using radiometric dating to see how much decay of certan things that were in the living organism sientists know how fast it happens so can tell how old they are(5 votes)
- it looks like a turtle shell(5 votes)
- Do things on land age differently than things in the water/sea?(3 votes)
yes, think of it this way. an animal dies on land, it is in the woods and is on the ground. so the flesh decays by natural resources( ants, other animals, time and bugs) and only the bones are left, it gets dirt on it, which turns to mud and which then has bacteria and chemicals, it gets buried and starts to harden to a fossil, it does not take as long as they say it does. okay now water, so diff chemicals in dirt, rather than in water, helps or prevents the process of decaying. and silt on the bottom of the ocean floor might make it better or harder to fossilize organic matter.(4 votes)
- How do fossils stay hard for so long(3 votes)
- This is because the sedimentary rock forms over time through sediment hardening. Once it hardens it’s a rock, however they are not too hard and supposedly can break easily if the rock isn’t that big, but the fossils themselves harden up because of the rock too.(4 votes)