—পৃথিবী সৃষ্টির আদি কথা—
পৃথিবীর সৃষ্টির আদি কথা বিজ্ঞানীদের কাছে অজানা জগতের এক অনন্য রহস্য ভেদ। পৃথিবী সৃষ্টির ইতিহাসে বিভিন্ন বিজ্ঞানীর মতভেদ ও ভিন্ন।
তবে সর্ব সম্মত ভাবে বিজ্ঞানীরা সিদ্ধান্তে স্থির করেন পৃথিবী সৃষ্টির দুটি বৈজ্ঞানিক মতবাদ —
¤ গ্রহ সৃষ্টির প্রকল্প,
¤নীহারিকা প্রকল্প
¤ গ্রহ সৃষ্টির প্রকল্প :-
এই মতবাদ অনুযায়ী প্রায় 500 থেকে 600 কোটি বছর পূর্বে জলন্ত সূর্যের অংশ বিচ্ছিন্ন হয়ে সৃষ্টি হয় পৃথিবীর। সৃষ্টির প্রথমে পৃথিবী বিভিন্ন মৌলের উত্তপ্ত গ্যাস ও জলীয় বাষ্পের ঘূর্ণায়মান বৃহৎ গোলক ছিল।
পৃথিবী সৃষ্টির সময় 5000°C-6000°C তাপমাত্রা ছিল। এই উচ্চ তাপমাত্রার কারণে হাইড্রোজেন (H), অক্সিজেন (O), কার্বন (C) প্রভৃতি মৌল গুলি মুক্ত অবস্থায় ছিল না। এরা বিভিন্ন অক্সাইড, কার্বাইড, নাইট্রাইড ইত্যাদি অজৈব যৌগে রূপান্তরিত ছিল।
কার্বন, নাইট্রোজেন (N) এবং অক্সিজেনের যৌগ গুলি —সায়ানোজেন [(CN)2], মিথেন (CH4), অ্যামোনিয়া (CH3), সায়ানাইড (CN—) ইত্যাদি গ্যাসীয় অবস্থায় ছিল।
কয়েকশো লক্ষ বছর ধরে গ্যাসীয় উপাদান গুলি ঘনীভূত হয়ে ঘনত্ব অনুযায়ী ভিন্ন ভিন্ন স্তরে বিন্যস্ত হয়। এভাবেই পৃথিবী ক্রমশ শীতল ও তরল থেকে কঠিনে পরিনত হয়। পৃথিবী সৃষ্টির শুরুতে জলীয় বাষ্প ঘনীভূত হয়ে অভিকর্ষের প্রভাবে বৃষ্টিপাতের আবির্ভাব ঘটে। পৃথিবীতে জলচক্রের জন্ম হয় ও উষ্ণতা হ্রাস পায়।
পৃথিবী কঠিন থেকে কঠিনে পরিনত হয় এবং বিশাল জলরাশি তথা সমুদ্রের সৃষ্টি হয়।
আর এই সমুদ্র থেকেই সৃষ্টি হয়েছে এককোষী থেকে বহুকোষী জীবের। কোটি কোটি বছর ধরে পর্যায়ক্রমিক বিবর্তনের ফলে সৃষ্টি হয়েছে উন্নত উদ্ভিদ ও প্রাণীর। পৃথিবী পরিনত হয়েছে বাসযোগ্য মনুষ্য ভূমিতে।
¤নীহারিকা প্রকল্প:-
এই মত অনুসারে সূর্যে বিভিন্ন প্রচন্ড বিস্ফোরণ হয় ও কিছু অংশ বিচ্ছিন্ন হয়ে যায় । কোটি কোটি বছর ধরে পর্যায় ক্রমে পৃথিবী ও অন্যান্য গ্রহের সৃষ্টি হয়।
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