no, this is not possible without giving each row a wrapper.
here's a pure css solution with a single containing wrapper (per row)
.row {
background-color: #ccc;
float: left;
margin: 10px 0;
padding: 1em;
width: 50%;
}
.a {
float: left;
width: 45%;
}
.b {
float: right;
width: 45%;
}
and the html
<div class="row">
<div class="a">Mofo break yo neck, yaonna chung fizzle, bizzle dizzle dang dolor boom shackalack augue. Fizzle izzle away sit its fo riz</div>
<div class="b">Lorizzle hizzle dolizzle sit amet, brizzle adipiscing elizzle. Nullam i saw beyonces tizzles and my pizzle went crizzle shizzlin dizzle, fo shizzle mah nizzle fo rizzle, mah home g-dizzle sizzle, suscipit quizzle, i saw beyonces tizzles and my pizzle went crizzle vizzle, arcu. Break yo neck, yall shiznit tortor. Sed eros. Ma nizzle izzle you son of a bizzle dapibizzle turpishizzle. Integizzle check out this velit sed fo.</div>
</div>
<div class="row">
<div class="a">Sizzle ullamcorpizzle. Shut the shizzle up sagittizzle dizzle a shiznit. Vestibulizzle you son of a bizzle ipsizzle primis izzle faucibus orci pot et ultrices posuere dope Fo shizzle; Crazy vestibulizzle. Fo shizzle my nizzle habitant morbi tristique senectus ma nizzle netizzle izzle tellivizzle famizzle turpis hizzle. Donizzle tempor hendrerit hizzle. Aliquizzle erat volutpat. </div>
<div class="b">Vivamizzle sagittis.rttitizzle izzle, boom shackalack hizzle, orci. Integizzle hizzle funky fresh lectus. </div>
</div>
<div class="row">
<div class="a">Donizzle tempor hendrerit hizzle. Aliquizzle erat volutpat. Things crunk fizzle, scelerisque bizzle, daahng dawg the bizzle, crackalackin shiznit, arcu. Daahng dawg elizzle. Crazy fermentizzle, est izzlot purizzle , bibendizzle sizzle amizzle, fo shizzle vehicula, fo shizzle my nizzle malesuada, shizznit. Aenizzle fizzle ipsizzle izzle est ullamcorpizzle tincidunt. Cool quizzle. Mauris ligula urna, tempizzle shut th</div>
<div class="b">Mofo break yo neck, yall fo shizzle izzle leo bibendum crackalackin. Vivamizzle shit tortor vizzle away. Brizzle malesuada fo magna. Dang commodo, nisl nizzle go to hizzle egestizzle, magna dolor w</div>
</div>
if you want a and b to have different background colors you will have to use height:100%