How can older rocks be found on top of younger rocks in a cross-section?​

So If the older rock is sedimentary, such as a stream deposit, the layers will indicate which way was up when deposited. When you find this layer overturned on top of a younger rock, it’s likely part of a fold structure and should have a trend matching other rocks showing a fold.

You already know from surveys that the complete section of the area has a layer of A below a layer of B. If you find A above B, some event overturned it

There is a marker bed such as a layer of volcanic ash that records a single event in the area, then you have a reference point in time.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.