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Scrat [10]
3 years ago
9

What index provides evidence of when different types of life evolved on Earth?

Biology
1 answer:
aev [14]3 years ago
4 0

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.

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The top layer of soil in the tundra that thaws in the summer is called the _____.
Degger [83]

Answer:

A.

Explanation:

The arctic soil is so cold that the ground beneath the tundra surface remains frozen all year. This permanently frozen ground is called permafrost. Each summer, when the sun warms the tundra surface, the top few inches of soil thaw. This melted part is called the active layer.

3 0
3 years ago
Which of the following is a true statement?Anabolic pathways build molecules, require energy, and are endergonic.Anabolic pathwa
expeople1 [14]

Answer:

A: Anabolic pathways build molecules, require energy and are endergonic

Explanation:

Anabolism and catabolism are the two important process of metabolism - a process through which cells get energy to drive various processes within the body and get rid of toxic wastes.

Anabolic and catabolic reactions can be described as opposing sides of the same coin. While anabolism refers to the various reactions that build up molecules within the cell, catabolism has to do with the breakdown of big or complex molecules into smaller ones.

Both processes involves energy. Anabolic reactions require energy to drive the building up process and therefore referred to as endergonic reactions. On the other hand, catabolic reactions liberate energy during the breaking down of complex molecules and therefore referred to exergonic reactions.

A good example of anabolic reaction is photosynthesis which involves the building up of carbohydrate (glucose) using carbon-dioxide, water molecule and energy while a good example of catabolic reaction is respiration which involves the breakdown of carbohydrates into carbon-dioxide, water molecules and the release of energy.

Hence, the only correct option is A.  

6 0
3 years ago
what is the characteristic of a cell membrane that controls which substances can enter and exit the cell
lorasvet [3.4K]

Answer:

selective permeability

Explanation:

The property or characteristic of cellular membrane to allow certain substances to pass through the cell is known as selective permeability. The movement of molecules and ions across the cell can be active or passive.

3 0
3 years ago
What is difference between plasma cells and memory cells, and how do they prevent you becoming ill??
Stolb23 [73]
The difference between them is that they are active in fighting infection. Plasma cells are active in defense during the first exposure to invaders like viruses or bacteria producing antibodies. Memory cells last longer and make a copy of the invaders. This allows an extremely rapid defense later in case of a second exposure.
5 0
3 years ago
The pathway leading from the striate cortex to the parietal lobe is known as the
Ray Of Light [21]
In the two-streams hypothesis, a model for the process of vision, information moves from the striate cortex to the parietal lobe by way of the morsel stream also called the where pathway. This pathway is involved with defining the spatial qualities of an object relative to the viewer. 
5 0
4 years ago
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