Scientists combine several well-tested techniques to find out the ages of fossils. The most important are Relative Dating, in which fossils and layers of rock are placed in order from older to younger, and Radiometric Dating, which allows the actual ages of certain types of rock to be calculated.
Relative Dating. Fossils are found in sedimentary rocks that formed when eroded sediments piled up in low-lying places such as river flood plains, lake bottoms or ocean floors. Sedimentary rock typically is layered, with the layers derived from different periods of sediment accumulation. Almost any place where the forces of erosion - or road crews - have carved through sedimentary rock is a good place to look for rock layers stacked up in the exposed rock face. When you look at a layer cake, you know that the layer at the bottom was the first one the baker put on the plate, and the upper ones were added later. In the same way, geologists figure out the relative ages of fossils and sedimentary rock layers; rock layers, and the fossils they contain, toward the bottom of a stack of sediments are older than those found higher in the stack.
Radiometric Dating. Until the middle of the last century, "older" or "younger" was the best scientists could do when assigning ages to fossils. There was no way to calculate an "absolute" age (in years) for any fossil or rock layer. But after scientists learned that the nuclear decay of radioactive elements takes place at a predictable rate, they realized that the traces of radioactive elements present in certain types of rock, such as hardened lava and tuff (formed from compacted volcanic ash), could be analyzed chemically to determine the ages, in years, of those rocks.
Putting Relative and Radiometric Dating Together. Once it was possible to measure the ages of volcanic layers in a stack of sedimentary rock, the entire sequence could be pinned to the absolute time scale. In the Wyoming landscape shown below left, for example, the gray ash layer was found to be 73 million years old. This means that fossils in rock layers below the tuff are older than 73 million years, and those above the tuff are younger. Fossils found embedded within the ash, including the fossil leaves shown below right, are the same age as the ash: 73 million years old. So, there for the relationship between the age of a fossil and the layer of rock in which it was found dates back to about the same time era.
- Got this out of an article, hope it helps! (:
But my guess its a oxygen? Or carbon dioxide?
Answer:
sorry I don't think I can do it that fast
Explanation:
Well first off every thing will be more expensive because we will have more money since we are not using it to buy food any more. we would get more money, save more money, and every thing will cost a lot more. Many people will lose jobs because they won't be making food any more (like people at mcdonalds) and then to get a job people will need higher intellect. The population of cows, pigs, and other animals that we eat will rise and they won't be domesticated any more (unless you want to keep a pet chicken, thats fine with me) and the evolution line might change. Then the downside is that the people live in a climate where it is mostly cloudy and dark will be more hungry and will probably move to warmer areas where they can get enough food. People in warmer climate can just sit outside for a few hours and they will be full and not hungry. As you can see if people began to use photosynthesis to get food. many things will change.
I hope this helped. :3
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answer: the parent can be a single organism
explanation:
it only takes one "parent" single celled organism to asexually reproduce through binary fission
it only takes one "parent" multi celled organism to asexually reproduce through fragmentation or budding
