Which of the following is true:

-Relative dating tells us how long ago something existed
-Disconformities are less common but usually far more conspicuous because the strata on either side are essentially
-Estimates indicate that the North American continent is being lowered at a rate of about 10 cm per 1000 yrs
-Most volcanoes are fed by conduits or pipes

To determine which statement is true, we'll examine each statement individually:

1. Relative dating tells us how long ago something existed: This statement is incorrect. Relative dating is a method used in geology to determine the order of events or objects relative to one another, but it does not provide precise ages or specific timeframes for when something existed.

2. Disconformities are less common but usually far more conspicuous because the strata on either side are essentially: This statement is incomplete. It seems to start explaining the characteristics of disconformities, which are geological features where there is a gap in the rock record between parallel layers of sedimentary rocks. Disconformities can indeed be conspicuous because the layers above and below the gap can have similar characteristics, making it challenging to recognize the missing section.

3. Estimates indicate that the North American continent is being lowered at a rate of about 10 cm per 1000 yrs: This statement is true. The North American continent is situated on tectonic plates, which are constantly moving. Some areas, such as parts of the West Coast, are slowly sinking due to tectonic forces. The estimated rate of subsidence for North America is approximately 10 centimeters per 1000 years.

4. Most volcanoes are fed by conduits or pipes: This statement is true. Volcanoes are formed when magma rises from the Earth's interior to the surface. This ascent of magma is facilitated by conduits or pipes within the Earth's crust. These channels allow the magma to reach the surface, leading to volcanic eruptions.

In summary, the true statement among the options provided is that most volcanoes are fed by conduits or pipes.