I don't know ... but using a bit of logic it must be something that can perform photosynthesis, so it would be green plants or some microbes that can do the opposite of respiration in order for higher order animals to feed off them.
You can't get a lion living very long without it's staple food, which happens to be another animal so it must be that whatever is at the beginning end of the food chain must be the creature that was created first.
Unless Allah (SWT) kept the crow alive without it's food, which is possible.
not bad. but photosynthesis didn't evolve until quite a while after life took hold on earth. the most primitive life known to us from physical evidence are unicellular organisms that get their energy needs from non-solar sources - geo-thermal pools, and not from breaking down sugars. these cells lack structures like chloroplasts and mitochondria.