Help me pls ASAP !!

If it takes 700 million years for half of your the uranium in a rock to decay into lead how old is a fossil that is:

a.) 50% uranium and 50% lead

b.) 25% uranium and 75% lead

Is there any species that went extinct in recent years due to natural causes (not caused by human interaction). if so, what caused it?

Pls in your opinion, what are the limiting factors that might affect the growth or diversity of our ecosystem? respond to this question in claim, evidence, reasoning format. 1. make your claim (i are the limiting factors that might affect the growth or diversity of our 2. follow the claim with 3 pieces of evidence. evidence may be taken from the reading, the videos, previous lessons, or googled answers. site sources, too. 3. use reasoning to explain why you chose your evidence.

Juan and carol were studying invertebrates in biology. they knew that segmented or earth worms preferred a dark, moist habitat. during this lab, they would be investigating the responses of organisms called planaria or dugesia tigrina. these were simple flatworms that still had a one-way digestive system and a very simple nervous system. juan and carol placed the planaria in a petri dish containing cool, distilled water that was partially covered with black paper. they shined a light on the dish. next, they removed the paper and placed a small amount of chicken liver at one end of the dish. they added a few large salt crystals to the water. finally, they added drops of hot water to the cool water in the petri dish. their results can be seen in the data table. according to their experiment, all but one conclusion is valid.