Sorry, David. I forgot about the quotations. I will make sure to follow this for my next questions.
Thanks, Symphony. We appreciate that. And thank you for editing your first post above so that it adheres to the guidelines.
“Although research in the earth and environmental sciences has pieced together narratives of ancient and historical environmental changes, there is still much left to learn about the nature and causes of changing climatic conditions through time”.
Please help me in understanding the grammatical form and function of “still much left to learn about the nature”.
"There is still much left to learn about X" means "Much about X still remains to be learned." The OED (The Oxford English Dictionary) classifies this use of "left" as a passive form of the verb "leave" (in the sense "too allow or cause to remain in the same place or condition"); however, in this passive there is no sense of agency:
(b) In passive without a sense of agency. to be left: to remain to be used or dealt with [. . .]
1822 C. Lamb in London Mag. Mar. 285/1 If you do not make haste to return, there will be little left to greet you, of me, or mine.
Within the infinitive clause of your example, the object of "learn" is "much" ("about the nature and causes of changing climatic conditions through time"). Compare:
A: Is there anything left to eat in the refrigerator?
B: Yes. There are plenty of leftovers in there. Have some Chinese food.