Answer to Question 1
Answer: The accretion process that built Earth is not entirely over. Small meteors and dust particles continue to add about 100,000 kilograms to Earth each day, which is negligible compared to the mass of Earth. Most of the incoming mass is fine space dust, and even the somewhat larger colliding objects are too small to notice, other than the occasional bright fireballs and meteor streaks (shooting stars) visible in the night sky.
Answer to Question 2
Answer: 1. The current heat flow from within Earth is approximately twice as high as can be accounted for by present-day radioactive decay in the crust and mantle. This suggests excess heat that remains from processes active in the past when Earth was hotter.
2. Ultramafic lava flows are found on Earth only among rocks more than 3 billion years old. Experiments reveal that these unique lava flows, the only known extrusive equivalents of peridotite, could only form at mantle temperatures several hundred degrees hotter than those estimated today.
