If the Earth were to start rotating more slowly, a number of significant effects would occur:

* Length of day: The day would become longer. A day is defined as the time it takes for the Earth to complete one full rotation on its axis. If the Earth rotates more slowly, it will take longer to complete one rotation, and the day will be longer.

* Tidal forces: The tidal forces exerted by the Moon and Sun would be greater. Tidal forces are the gravitational forces exerted by these celestial bodies on the Earth. The slower rotation of the Earth would cause the tidal forces to be stronger, resulting in higher high tides and lower low tides.

* Climate change: The Earth's climate would be affected. The slower rotation of the Earth would cause the oceans to circulate more slowly, which would disrupt the global ocean currents. This would lead to changes in the Earth's climate, such as changes in temperature and precipitation patterns.

* Atmospheric circulation: The Earth's atmospheric circulation would be affected. The slower rotation of the Earth would cause the Coriolis effect to be weaker. The Coriolis effect is a force that deflects objects moving in the atmosphere and oceans. The weaker Coriolis effect would lead to changes in the Earth's atmospheric circulation, such as changes in wind patterns and storm tracks.

* Magnetic field: The Earth's magnetic field would be affected. The Earth's magnetic field is generated by the movement of molten iron in the Earth's core. The slower rotation of the Earth would cause the movement of molten iron to slow down, which would lead to a weaker magnetic field.

Overall, the slower rotation of the Earth would have a significant impact on the planet's environment, climate, and life forms.