Most of the world's iron ore, including that found in northern Minnesota, formed during the middle Precambrian period, ranging in
age from 1.8 to 2.5 billion years old. They are composed of alternating layers of iron-rich material, most often magnetite or
hematite, and silica. These iron oxide minerals formed on the ocean floor, creating the banded iron deposits you see here. What
was the source of the oxygen that helped to produce these deposits?
The oxygen that was released into the atmosphere as a by-product of
photosynthesis caused iron deposits to oxidize creating the iron oxide
minerals,
Photosynthetic organisms making oxygen as a by-product of
photosynthesis and the oxygen reacted with the iron dissolved in seawater
to form iron oxide minerals.
The decomposition of carbon-based life forms in the oceans released
oxygen and carbon dioxide. These gases reacted with the iron deposits
forming the minerals mentioned,
In Earth's early biosphere, there were not organisms that underwent
aerobic cellular respiration and an excess of oxygen built up in the
atmosphere. This oxygen reacted with iron deposits to form iron oxide
minerals.
Eliminate
15)
Peppered moths come in two colors, black and white. What did Kettlewell show, with regard to peppered moth populations and

What are the three ways that an object can accelerate

Aheat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. the same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. heat pumps are widely used for home heating. you can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat qh, warming the indoors. perhaps this seems a little silly, but consider the following. electricity can be directly used to heat a home by passing an electric current through a heating coil. this is a direct, 100% conversion of work to heat. that is, 19.0 \rm kw of electric power (generated by doing work at the rate 19.0 kj/s at the power plant) produces heat energy inside the home at a rate of 19.0 kj/s. suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. note: with a refrigerator, "what you get" is heat removed. but with a heat pump, "what you get" is heat delivered. so the coefficient of performance of a heat pump is k=qh/win. an average price for electricity is about 40 mj per dollar. a furnace or heat pump will run typically 200 hours per month during the winter. what does one month's heating cost in the home with a 16.0 kw electric heater? what does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating?

What equation is used to calculate the weight of an object on a plant ?