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! (:
A. Carbon
Explanation:
because during photosynthesis, the cells use carbon dioxide and the light from the sun and that makes sugar molecules.
Answer:
The correct answer is- C. allows new species to occupy different habitats.
Explanation:
Adaptive evolution is a type of evolution that allows the generation of new species from an ancestral species. This evolution occurs mainly due to the separation of habitat between two populations of species.
So when some members of ancestral species get new habitat which is different in ways like in food availability, food type, environment, etc then this isolated population adapts to the new environment by doing changes in their gene which results and the development of new species. So the correct answer is C.
Answer: A.) Heterotrophs compete for the same food source.
A food chain is a linear sequence in which food and energy is being transfered when one organism is fed the another organism in an ecosystem. A food web is a interconnection of two or more food chains. Heterotrophs are organisms which are dependent upon other organisms for the food requirement. In the given condition, the lizard and frogs are the heterotrophs which are dependent upon insects for their food requirement.
<em>Hence, heterotrophs compete for the same food source is the correct statement to describe the relationship between the lizard and the frog on the food web. </em>
