Endosymbiotic Theory

Endosymbiotic Theory

By Tara Hovsepian

​Some text here about the topic of discussion.

​SCIENTIFIC EXPLANATION OF THE ORIGIN OF LIFE ON EARTH The Earth formed roughly 4.5 billion years ago, and life probably began between 3.5 and 3.9 billion years ago.

Fill in the Blanks

The Earth formed roughly

billion years ago, and life probably began between 3.5 and 3.9 billion years ago.

​For many millions of years, early Earth was pummeled by asteroids and other celestial objects. Temperatures also would have been very high (with water taking the form of a gas, not a liquid). The first life might have emerged during a break in the asteroid bombardment, between 4.4 and 4.0 billion years ago, when it was cool enough for water to condense into oceans. However, a second bombardment happened about 3.9 billion years ago. It’s likely after this final go-round that Earth became capable of supporting sustained life.

​Some text here about the topic of discussion.

Multiple Choice

When the Earth began, temperatures also would have been very high (with water taking the form of a ____.

• gas

• liquid

• liquid and gas

• crystals