If the Atlantic seafloor is spreading at cm/year and is now 6400 km wide, how long ago were the continents in

Question

If the Atlantic seafloor is spreading at cm/year and is now 6400 km wide, how long ago were the continents in contact?

Answer 1

Number of cm the seafloor has spread: 6400 x 1000 x 100 = 640,000,000. At one cm per year, that is 640,000,000 (640 million) years.

Unless of course you mean it spreads 1cm per year on each side of the mid-atlantic ridge, in which case it would be half of that, or 320,000,000 (320 million) years.
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Answer 2

Time seems to be an awareness factor. The fault line in the Ocean is referred to as a trench. It widens with growth and the strength of the magnetic field. The magnetic field strength is based upon the mass. You have heard that the first land mass was named Pangaea? Give it some thought? If water was not covering the Earth would not the Earth be as Mars. There is a deep trench on Mars too. You can perform a simple demonstration on how this phenomena occurs.
Find a strong disc shaped magnet of neodymium about the size of a quarter, a sheet of clear plastic and micro meteorites. The magnet can be purchased from Radio Shack, the plastic can be salvaged from packing and the meteorites can be gathered by dragging the magnet through beach or river dry sand. Do not use iron filings because they are magnetized. Hold the magnet edgewise to the underside plastic. Take a pinch of dust and drop it on the plastic. Twist the magnet and watch the ball form. Keep adding the dust to simulate growth and the hemisphere will develop a trench.
Science tags all phenomena to TIME. It has no real relevance. If for instance our planet had a year long meteor shower growth would have been accelerated as much as each pinch of dust you added to your demonstration.

Answer 3

Pangea is said to have taken place about 200 million years ago