Indian Institute of Science

Hello,
Basic Qualification for Eligibility:
First Class in Bachelor or an equivalent degree in Physical Chemical or Biological Sciences including Biotechnology Pharmaceutical Veterinary Sciences and Agricultural Sciences
Candidates who seek admission to the Integrated Ph D programmes at IISc should qualify in JAM exam and must submit the IISc online application during February March The JAM result must be updated online in the Applicant Interface immediately after the JAM results are announced
Candidates who have cleared JEST and seek admission to the Integrated Ph D programme in the Physical Sciences are also eligible to apply
Each year the Institute admits 50 to 60 students 15 to 18 in the Biological Sciences
The short listing of candidates for interview is done based on the performance in JAM and JEST nterviews are held in the month of May 2019
Selection for Biological Physical and Mathematical Sciences selection will be based on the combined performance in the Test and in Interview
Good Luck.

Dear Archita,
Certain points in this regards:
(#1) Only PCB wouldn't help. Some entrance exam requires maths as a mandatory subject also because of the huge involvement of physics, mechanics and astronomy. It is really important to have strong understanding of physics, chemistry and biology. Do not worry if you are not good with maths as you can still do something with the other subjects. You must remember that as far as Astrobiology is concerned you will be mainly self-taught.
(#2) Astrobiology, astrochemistry are some field which are under-evolve in India. You know that there is only one serious, dedicated institute in India which is sepcilized in this field.
Indian Astrobiology Research Center - They offers International Diploma programme in Astrobiology. However to widening the scope, you must to go abroad.
(#3) After your Bachelor's, Masters, and essentially Ph.D. you will work as Faculty or Research Analyst in Earth Science department or IARC itself. Nothing steps involved in it. IARC offers 4 months of Diploma in astrobiology.