There are all sorts of ways to reconstruct the history of life on Earth. Pinning down when specific events occurred is often tricky, though. For this, biologists depend mainly on dating the rocks in which fossils are found, and by looking at the “molecular clocks” in the DNA of living organisms.
There are problems with each of these methods. The fossil record is like a movie with most of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.
Modern genetics allows scientists to measure how different species are from each other at a molecular level, and thus to estimate how much time has passed since a single lineage split into different species. Confounding factors rack up for species that are very distantly related, making the earlier dates more uncertain.
These difficulties mean that the dates in the timeline should be taken as approximate. As a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.
The nitrogen cycle is impacted by humanswhenever fertilizer is applied to farmland to help crops grow. This adds nitrates to the soil. If soil erodes, the nitrates are transported and deposited in the nearest body of water. This can cause algae to overgrow in a process called eutrophication. The lake will run out of oxygen as the algae die off and bacteria begin their decomposition.Sessile organisms are greatly affected.
Answer:
10 % of the energy (i.e., 50 calories) is converted to biomass
. This efficiency of energy transformation is high
Answer:
Spongy bone is well adapted to accept stress in many directions, which makes it good for shock absorption
Explanation:
Spongy bone tissue is less compact and always present towards the interior of the bone and is covered by compact bone. Spongy bone tissue has lamellae that are arranged in an irregular pattern. The thin irregular columns of lamellae are called trabeculae.
The trabeculae of spongy bone tissues are precisely arranged along the line of stress. This feature of spongy bones allows them to resist the stress applied from many directions and to transfer the force making them a good shock absorber. The final arrangement of trabeculae is achieved only after the person learns the locomotory movements completely.
