Whenever. Nobody really knows. Not even geologists. I bet they are figuring it out, but that haven't had luck yet.
Hope this helps ;)
Answer:
muscle cells hope its right
Because the rock is laid down over time, the oldest rock (and fossils or whatever) will be in the lowest layer. As you go up, the age decreases - you are looking at younger rocks.
This doesn't tell you the *absolute* age of the rocks - you can't say from this evidence whether they are 100 million or 500 million years old. But you can see changes over history and you can get an ordering in time.
Hello there buddy,
Your correct answer would be "protein". Protein is the organic molecule that is needed for a active transport.
I hope this helps.
~Jurgen