Which statements describe how the geologic timescale is organized? Select all that apply. by intervals of time equal in length over Earth's 4.6 billion year history
by major changes in ancient Earth's climate or major natural disasters
by the appearance, disappearance, or change in dominance (frequency) of particular fossil groups
by the date that fossils were discovered by paleontologists

The direction a chemical reaction occurs is represented by an arrow 

Mars and earth have quite a few things in common. both are  terrestrial planets, both are located within the sun’s  habitable zone, both have  polar ice caps, similarly  tilted axes, and similar  variations in temperature. and according to some of the latest scientific data obtained by rovers and atmospheric probes, it is now known that mars once had a  dense atmosphere  and was covered with  warm, flowing water.